diff --git a/.travis.yml b/.travis.yml
index 9de3c6c155d..04b6b07e695 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -10,7 +10,7 @@ env:
       --data @- << DATA\n{
       "state": "$0",
       "description": "$1",
-      "context": "travis-ci/$NAME/$(python --version)",
+      "context": "travis-ci/$NAME",
       "target_url": "https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID"
       }\nDATA'
 
@@ -145,17 +145,20 @@ matrix:
         - sudo chmod a+rw /dev/loop0
         - dd if=/dev/zero bs=512 count=2048 of=DISK
         - losetup /dev/loop0 DISK
+        - CFLAGS="-Werror -Wno-format"
       script:
         # Check that example compiles
+        - export CFLAGS="-Werror -Wno-format"
         - sed -n '/``` c++/,/```/{/```/d;p;}' $LITTLEFS/README.md > main.cpp
         - python tools/make.py -t GCC_ARM -m K82F --source=. --build=BUILD/K82F/GCC_ARM -j0
         # Run local littlefs tests
-        - CFLAGS="-Wno-format" make -C$LITTLEFS/littlefs test QUIET=1
+        - make -C$LITTLEFS/littlefs test QUIET=1
         # Run local littlefs tests with set of variations
-        - CFLAGS="-Wno-format -DLFS_READ_SIZE=64  -DLFS_PROG_SIZE=64"      make -C$LITTLEFS/littlefs test QUIET=1
-        - CFLAGS="-Wno-format -DLFS_READ_SIZE=1   -DLFS_PROG_SIZE=1"       make -C$LITTLEFS/littlefs test QUIET=1
-        - CFLAGS="-Wno-format -DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512"     make -C$LITTLEFS/littlefs test QUIET=1
-        - CFLAGS="-Wno-format -DLFS_BLOCK_COUNT=1023 -DLFS_LOOKAHEAD=2048" make -C$LITTLEFS/littlefs test QUIET=1
+        - make -C$LITTLEFS/littlefs test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=64  -DLFS_PROG_SIZE=64"
+        - make -C$LITTLEFS/littlefs test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=1   -DLFS_PROG_SIZE=1"
+        - make -C$LITTLEFS/littlefs test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512"
+        - make -C$LITTLEFS/littlefs test QUIET=1 CFLAGS+="-DLFS_BLOCK_COUNT=1023 -DLFS_LOOKAHEAD=2048"
+        - make -C$LITTLEFS/littlefs clean test QUIET=1 CFLAGS+="-DLFS_NO_INTRINSICS"
         # Self-hosting littlefs fuzz test with littlefs-fuse
         - make -Clittlefs_fuse
         - littlefs_fuse/lfs --format /dev/loop0
@@ -164,7 +167,30 @@ matrix:
         - mkdir MOUNT/littlefs
         - cp -r $(git ls-tree --name-only HEAD $LITTLEFS/littlefs/) MOUNT/littlefs
         - ls MOUNT/littlefs
-        - CFLAGS="-Wno-format" make -CMOUNT/littlefs -B test_dirs QUIET=1
+        - CFLAGS="-Wno-format" make -CMOUNT/littlefs -B test_dirs test_files QUIET=1
+        # Compile and find the code size with smallest configuration
+        - cd $TRAVIS_BUILD_DIR/$LITTLEFS/littlefs
+        - make clean size
+            CC='arm-none-eabi-gcc -mthumb'
+            OBJ="$(ls lfs*.o | tr '\n' ' ')"
+            CFLAGS+="-DLFS_NO{ASSERT,DEBUG,WARN,ERROR}"
+            | tee sizes
+      after_success:
+        # update status if we succeeded, compare with master if possible
+        - |
+          CURR=$(tail -n1 sizes | awk '{print $1}')
+          PREV=$(curl https://api.github.com/repos/$TRAVIS_REPO_SLUG/status/master \
+              | jq -re "select(.sha != \"$TRAVIS_COMMIT\")
+                  | .statuses[] | select(.context == \"travis-ci/$NAME\").description
+                  | capture(\"code size is (?<size>[0-9]+)\").size" \
+              || echo 0)
+
+          STATUSM="Passed, code size is ${CURR}B"
+          if [ "$PREV" -ne 0 ]
+          then
+              STATUSM="$STATUSM ($(python -c "print '%+.2f' % (100*($CURR-$PREV)/$PREV.0)")%)"
+          fi
+        - bash -c "$STATUS" success "$STATUSM"
 
     - &mbed-2
       env: NAME=mbed2-NXP
diff --git a/features/filesystem/littlefs/TESTS/filesystem/dirs/main.cpp b/features/filesystem/littlefs/TESTS/filesystem/dirs/main.cpp
index 42f60f0d4ed..f88b6280da7 100644
--- a/features/filesystem/littlefs/TESTS/filesystem/dirs/main.cpp
+++ b/features/filesystem/littlefs/TESTS/filesystem/dirs/main.cpp
@@ -18,7 +18,6 @@
 #include "unity.h"
 #include "utest.h"
 #include <stdlib.h>
-#include <errno.h>
 
 using namespace utest::v1;
 
@@ -354,7 +353,7 @@ void test_directory_remove()
         res = fs.mount(&bd);
         TEST_ASSERT_EQUAL(0, res);
         res = fs.remove("potato");
-        TEST_ASSERT_EQUAL(-EINVAL, res);
+        TEST_ASSERT_EQUAL(-ENOTEMPTY, res);
         res = fs.remove("potato/sweet");
         TEST_ASSERT_EQUAL(0, res);
         res = fs.remove("potato/baked");
@@ -536,7 +535,7 @@ void test_directory_rename()
         res = fs.mkdir("warmpotato/mushy", 0777);
         TEST_ASSERT_EQUAL(0, res);
         res = fs.rename("hotpotato", "warmpotato");
-        TEST_ASSERT_EQUAL(-EINVAL, res);
+        TEST_ASSERT_EQUAL(-ENOTEMPTY, res);
         res = fs.remove("warmpotato/mushy");
         TEST_ASSERT_EQUAL(0, res);
         res = fs.rename("hotpotato", "warmpotato");
@@ -600,7 +599,7 @@ void test_directory_rename()
         res = fs.rename("warmpotato/fried", "coldpotato/fried");
         TEST_ASSERT_EQUAL(0, res);
         res = fs.remove("coldpotato");
-        TEST_ASSERT_EQUAL(-EINVAL, res);
+        TEST_ASSERT_EQUAL(-ENOTEMPTY, res);
         res = fs.remove("warmpotato");
         TEST_ASSERT_EQUAL(0, res);
         res = fs.unmount();
diff --git a/features/filesystem/littlefs/TESTS/filesystem_retarget/dirs/main.cpp b/features/filesystem/littlefs/TESTS/filesystem_retarget/dirs/main.cpp
index 31d271b1212..0c91ef5a5fc 100644
--- a/features/filesystem/littlefs/TESTS/filesystem_retarget/dirs/main.cpp
+++ b/features/filesystem/littlefs/TESTS/filesystem_retarget/dirs/main.cpp
@@ -13,12 +13,12 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+#include <errno.h>
 #include "mbed.h"
 #include "greentea-client/test_env.h"
 #include "unity.h"
 #include "utest.h"
 #include <stdlib.h>
-#include <errno.h>
 
 using namespace utest::v1;
 
@@ -354,7 +354,7 @@ void test_directory_remove()
         res = fs.mount(&bd);
         TEST_ASSERT_EQUAL(0, res);
         res = remove("/fs/" "potato");
-        TEST_ASSERT_EQUAL(EINVAL, errno);
+        TEST_ASSERT_EQUAL(ENOTEMPTY, errno);
         res = remove("/fs/" "potato/sweet");
         TEST_ASSERT_EQUAL(0, res);
         res = remove("/fs/" "potato/baked");
@@ -536,7 +536,7 @@ void test_directory_rename()
         res = mkdir("/fs/" "warmpotato/mushy", 0777);
         TEST_ASSERT_EQUAL(0, res);
         res = rename("/fs/" "hotpotato", "/fs/" "warmpotato");
-        TEST_ASSERT_EQUAL(EINVAL, errno);
+        TEST_ASSERT_EQUAL(ENOTEMPTY, errno);
         res = remove("/fs/" "warmpotato/mushy");
         TEST_ASSERT_EQUAL(0, res);
         res = rename("/fs/" "hotpotato", "/fs/" "warmpotato");
@@ -600,7 +600,7 @@ void test_directory_rename()
         res = rename("/fs/" "warmpotato/fried", "/fs/" "coldpotato/fried");
         TEST_ASSERT_EQUAL(0, res);
         res = remove("/fs/" "coldpotato");
-        TEST_ASSERT_EQUAL(EINVAL, errno);
+        TEST_ASSERT_EQUAL(ENOTEMPTY, errno);
         res = remove("/fs/" "warmpotato");
         TEST_ASSERT_EQUAL(0, res);
         res = fs.unmount();
diff --git a/features/filesystem/littlefs/littlefs/.gitignore b/features/filesystem/littlefs/littlefs/.gitignore
new file mode 100644
index 00000000000..36f92cd81cb
--- /dev/null
+++ b/features/filesystem/littlefs/littlefs/.gitignore
@@ -0,0 +1,9 @@
+# Compilation output
+*.o
+*.d
+*.a
+
+# Testing things
+blocks/
+lfs
+test.c
diff --git a/features/filesystem/littlefs/littlefs/.travis.yml b/features/filesystem/littlefs/littlefs/.travis.yml
index c17af8b17bb..2c6139fefce 100644
--- a/features/filesystem/littlefs/littlefs/.travis.yml
+++ b/features/filesystem/littlefs/littlefs/.travis.yml
@@ -1,47 +1,223 @@
+# Environment variables
+env:
+  global:
+    - CFLAGS=-Werror
+
+# Common test script
 script:
-    # make sure example can at least compile
-    - sed -n '/``` c/,/```/{/```/d; p;}' README.md > test.c &&
-      CFLAGS='
+  # make sure example can at least compile
+  - sed -n '/``` c/,/```/{/```/d; p;}' README.md > test.c &&
+    make all CFLAGS+="
         -Duser_provided_block_device_read=NULL
         -Duser_provided_block_device_prog=NULL
         -Duser_provided_block_device_erase=NULL
         -Duser_provided_block_device_sync=NULL
-        -include stdio.h -Werror' make all size
+        -include stdio.h"
+
+  # run tests
+  - make test QUIET=1
+
+  # run tests with a few different configurations
+  - make test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=1      -DLFS_PROG_SIZE=1"
+  - make test QUIET=1 CFLAGS+="-DLFS_READ_SIZE=512    -DLFS_PROG_SIZE=512"
+  - make test QUIET=1 CFLAGS+="-DLFS_BLOCK_COUNT=1023 -DLFS_LOOKAHEAD=2048"
+
+  - make clean test QUIET=1 CFLAGS+="-DLFS_NO_INTRINSICS"
+
+  # compile and find the code size with the smallest configuration
+  - make clean size
+        OBJ="$(ls lfs*.o | tr '\n' ' ')"
+        CFLAGS+="-DLFS_NO{ASSERT,DEBUG,WARN,ERROR}"
+        | tee sizes
+
+  # update status if we succeeded, compare with master if possible
+  - |
+    if [ "$TRAVIS_TEST_RESULT" -eq 0 ]
+    then
+        CURR=$(tail -n1 sizes | awk '{print $1}')
+        PREV=$(curl https://api.github.com/repos/$TRAVIS_REPO_SLUG/status/master \
+            | jq -re "select(.sha != \"$TRAVIS_COMMIT\")
+                | .statuses[] | select(.context == \"$STAGE/$NAME\").description
+                | capture(\"code size is (?<size>[0-9]+)\").size" \
+            || echo 0)
 
-    # run tests
-    - make test QUIET=1
+        STATUS="Passed, code size is ${CURR}B"
+        if [ "$PREV" -ne 0 ]
+        then
+            STATUS="$STATUS ($(python -c "print '%+.2f' % (100*($CURR-$PREV)/$PREV.0)")%)"
+        fi
+    fi
 
-    # run tests with a few different configurations
-    - CFLAGS="-DLFS_READ_SIZE=1   -DLFS_PROG_SIZE=1"       make test QUIET=1
-    - CFLAGS="-DLFS_READ_SIZE=512 -DLFS_PROG_SIZE=512"     make test QUIET=1
-    - CFLAGS="-DLFS_BLOCK_COUNT=1023 -DLFS_LOOKAHEAD=2048" make test QUIET=1
+# CI matrix
+jobs:
+  include:
+    # native testing
+    - stage: test
+      env:
+        - STAGE=test
+        - NAME=littlefs-x86
+
+    # cross-compile with ARM (thumb mode)
+    - stage: test
+      env:
+        - STAGE=test
+        - NAME=littlefs-arm
+        - CC="arm-linux-gnueabi-gcc --static -mthumb"
+        - EXEC="qemu-arm"
+      install:
+        - sudo apt-get install gcc-arm-linux-gnueabi qemu-user
+        - arm-linux-gnueabi-gcc --version
+        - qemu-arm -version
+
+    # cross-compile with PowerPC
+    - stage: test
+      env:
+        - STAGE=test
+        - NAME=littlefs-powerpc
+        - CC="powerpc-linux-gnu-gcc --static"
+        - EXEC="qemu-ppc"
+      install:
+        - sudo apt-get install gcc-powerpc-linux-gnu qemu-user
+        - powerpc-linux-gnu-gcc --version
+        - qemu-ppc -version
+
+    # cross-compile with MIPS
+    - stage: test
+      env:
+        - STAGE=test
+        - NAME=littlefs-mips
+        - CC="mips-linux-gnu-gcc --static"
+        - EXEC="qemu-mips"
+      install:
+        - sudo add-apt-repository -y "deb http://archive.ubuntu.com/ubuntu/ xenial main universe"
+        - sudo apt-get -qq update
+        - sudo apt-get install gcc-mips-linux-gnu qemu-user
+        - mips-linux-gnu-gcc --version
+        - qemu-mips -version
 
     # self-host with littlefs-fuse for fuzz test
-    - make -C littlefs-fuse
+    - stage: test
+      env:
+        - STAGE=test
+        - NAME=littlefs-fuse
+      install:
+        - sudo apt-get install libfuse-dev
+        - git clone --depth 1 https://github.com/geky/littlefs-fuse
+        - fusermount -V
+        - gcc --version
+      before_script:
+        # setup disk for littlefs-fuse
+        - rm -rf littlefs-fuse/littlefs/*
+        - cp -r $(git ls-tree --name-only HEAD) littlefs-fuse/littlefs
+
+        - mkdir mount
+        - sudo chmod a+rw /dev/loop0
+        - dd if=/dev/zero bs=512 count=2048 of=disk
+        - losetup /dev/loop0 disk
+      script:
+        # self-host test
+        - make -C littlefs-fuse
+
+        - littlefs-fuse/lfs --format /dev/loop0
+        - littlefs-fuse/lfs /dev/loop0 mount
 
-    - littlefs-fuse/lfs --format /dev/loop0
-    - littlefs-fuse/lfs /dev/loop0 mount
+        - ls mount
+        - mkdir mount/littlefs
+        - cp -r $(git ls-tree --name-only HEAD) mount/littlefs
+        - cd mount/littlefs
+        - ls
+        - make -B test_dirs test_files QUIET=1
 
-    - ls mount
-    - mkdir mount/littlefs
-    - cp -r $(git ls-tree --name-only HEAD) mount/littlefs
-    - cd mount/littlefs
-    - ls
-    - make -B test_dirs QUIET=1
+      # Automatically update releases
+    - stage: deploy
+      env:
+        - STAGE=deploy
+        - NAME=deploy
+      script:
+        # Update tag for version defined in lfs.h
+        - LFS_VERSION=$(grep -ox '#define LFS_VERSION .*' lfs.h | cut -d ' ' -f3)
+        - LFS_VERSION_MAJOR=$((0xffff & ($LFS_VERSION >> 16)))
+        - LFS_VERSION_MINOR=$((0xffff & ($LFS_VERSION >>  0)))
+        - LFS_VERSION="v$LFS_VERSION_MAJOR.$LFS_VERSION_MINOR"
+        - echo "littlefs version $LFS_VERSION"
+        - |
+          curl -u $GEKY_BOT_RELEASES -X POST \
+            https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs \
+            -d "{
+              \"ref\": \"refs/tags/$LFS_VERSION\",
+              \"sha\": \"$TRAVIS_COMMIT\"
+            }"
+        - |
+          curl -f -u $GEKY_BOT_RELEASES -X PATCH \
+            https://api.github.com/repos/$TRAVIS_REPO_SLUG/git/refs/tags/$LFS_VERSION \
+            -d "{
+              \"sha\": \"$TRAVIS_COMMIT\"
+            }"
+        # Create release notes from commits
+        - LFS_PREV_VERSION="v$LFS_VERSION_MAJOR.$(($LFS_VERSION_MINOR-1))"
+        - |
+          if [ $(git tag -l "$LFS_PREV_VERSION") ]
+          then
+            curl -u $GEKY_BOT_RELEASES -X POST \
+                https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases \
+                -d "{
+                    \"tag_name\": \"$LFS_VERSION\",
+                    \"name\": \"$LFS_VERSION\"
+                }"
+            RELEASE=$(
+                curl -f https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases/tags/$LFS_VERSION
+            )
+            CHANGES=$(
+                git log --oneline $LFS_PREV_VERSION.. --grep='^Merge' --invert-grep
+            )
+            curl -f -u $GEKY_BOT_RELEASES -X PATCH \
+                https://api.github.com/repos/$TRAVIS_REPO_SLUG/releases/$(
+                    jq -r '.id' <<< "$RELEASE"
+                ) \
+                -d "$(
+                    jq -s '{
+                        "body": ((.[0] // "" | sub("(?<=\n)#+ Changes.*"; ""; "mi"))
+                            + "### Changes\n\n" + .[1])
+                    }' <(jq '.body' <<< "$RELEASE") <(jq -sR '.' <<< "$CHANGES")
+                )"
+          fi
 
+# Manage statuses
 before_install:
-    - fusermount -V
-    - gcc --version
+  - |
+    curl -u $GEKY_BOT_STATUSES -X POST \
+        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
+        -d "{
+            \"context\": \"$STAGE/$NAME\",
+            \"state\": \"pending\",
+            \"description\": \"${STATUS:-In progress}\",
+            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
+        }"
 
-install:
-    - sudo apt-get install libfuse-dev
-    - git clone --depth 1 https://github.com/geky/littlefs-fuse
+after_failure:
+  - |
+    curl -u $GEKY_BOT_STATUSES -X POST \
+        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
+        -d "{
+            \"context\": \"$STAGE/$NAME\",
+            \"state\": \"failure\",
+            \"description\": \"${STATUS:-Failed}\",
+            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
+        }"
 
-before_script:
-    - rm -rf littlefs-fuse/littlefs/*
-    - cp -r $(git ls-tree --name-only HEAD) littlefs-fuse/littlefs
+after_success:
+  - |
+    curl -u $GEKY_BOT_STATUSES -X POST \
+        https://api.github.com/repos/$TRAVIS_REPO_SLUG/statuses/${TRAVIS_PULL_REQUEST_SHA:-$TRAVIS_COMMIT} \
+        -d "{
+            \"context\": \"$STAGE/$NAME\",
+            \"state\": \"success\",
+            \"description\": \"${STATUS:-Passed}\",
+            \"target_url\": \"https://travis-ci.org/$TRAVIS_REPO_SLUG/jobs/$TRAVIS_JOB_ID\"
+        }"
 
-    - mkdir mount
-    - sudo chmod a+rw /dev/loop0
-    - dd if=/dev/zero bs=512 count=2048 of=disk
-    - losetup /dev/loop0 disk
+# Job control
+stages:
+    - name: test
+    - name: deploy
+      if: branch = master
diff --git a/features/filesystem/littlefs/littlefs/DESIGN.md b/features/filesystem/littlefs/littlefs/DESIGN.md
index 75487cacb8c..04a119f2719 100644
--- a/features/filesystem/littlefs/littlefs/DESIGN.md
+++ b/features/filesystem/littlefs/littlefs/DESIGN.md
@@ -27,16 +27,17 @@ cheap and can be very granular. For NOR flash specifically, byte-level
 programs are quite common. Erasing, however, requires an expensive operation
 that forces the state of large blocks of memory to reset in a destructive
 reaction that gives flash its name. The [Wikipedia entry](https://en.wikipedia.org/wiki/Flash_memory)
-has more information if you are interesting in how this works.
+has more information if you are interested in how this works.
 
 This leaves us with an interesting set of limitations that can be simplified
 to three strong requirements:
 
 1. **Power-loss resilient** - This is the main goal of the littlefs and the
-   focus of this project. Embedded systems are usually designed without a
-   shutdown routine and a notable lack of user interface for recovery, so
-   filesystems targeting embedded systems must be prepared to lose power at
-   any given time.
+   focus of this project.
+
+   Embedded systems are usually designed without a shutdown routine and a
+   notable lack of user interface for recovery, so filesystems targeting
+   embedded systems must be prepared to lose power at any given time.
 
    Despite this state of things, there are very few embedded filesystems that
    handle power loss in a reasonable manner, and most can become corrupted if
@@ -52,7 +53,8 @@ to three strong requirements:
    which stores a file allocation table (FAT) at a specific offset from the
    beginning of disk. Every block allocation will update this table, and after
    100,000 updates, the block will likely go bad, rendering the filesystem
-   unusable even if there are many more erase cycles available on the storage.
+   unusable even if there are many more erase cycles available on the storage
+   as a whole.
 
 3. **Bounded RAM/ROM** - Even with the design difficulties presented by the
    previous two limitations, we have already seen several flash filesystems
@@ -72,7 +74,7 @@ to three strong requirements:
 
 ## Existing designs?
 
-There are of course, many different existing filesystem. Heres a very rough
+There are of course, many different existing filesystem. Here is a very rough
 summary of the general ideas behind some of them.
 
 Most of the existing filesystems fall into the one big category of filesystem
@@ -80,7 +82,7 @@ designed in the early days of spinny magnet disks. While there is a vast amount
 of interesting technology and ideas in this area, the nature of spinny magnet
 disks encourage properties, such as grouping writes near each other, that don't
 make as much sense on recent storage types. For instance, on flash, write
-locality is not important and can actually increase wear destructively.
+locality is not important and can actually increase wear.
 
 One of the most popular designs for flash filesystems is called the
 [logging filesystem](https://en.wikipedia.org/wiki/Log-structured_file_system).
@@ -94,7 +96,7 @@ filesystem can easily be designed to be resilient to power loss. The
 journaling component of most modern day filesystems is actually a reduced
 form of a logging filesystem. However, logging filesystems have a difficulty
 scaling as the size of storage increases. And most filesystems compensate by
-caching large parts of the filesystem in RAM, a strategy that is unavailable
+caching large parts of the filesystem in RAM, a strategy that is inappropriate
 for embedded systems.
 
 Another interesting filesystem design technique is that of [copy-on-write (COW)](https://en.wikipedia.org/wiki/Copy-on-write).
@@ -107,14 +109,14 @@ where the COW data structures are synchronized.
 ## Metadata pairs
 
 The core piece of technology that provides the backbone for the littlefs is
-the concept of metadata pairs. The key idea here, is that any metadata that
+the concept of metadata pairs. The key idea here is that any metadata that
 needs to be updated atomically is stored on a pair of blocks tagged with
 a revision count and checksum. Every update alternates between these two
 pairs, so that at any time there is always a backup containing the previous
 state of the metadata.
 
 Consider a small example where each metadata pair has a revision count,
-a number as data and the xor of the block as a quick checksum. If
+a number as data, and the XOR of the block as a quick checksum. If
 we update the data to a value of 9, and then to a value of 5, here is
 what the pair of blocks may look like after each update:
 ```
@@ -149,7 +151,7 @@ check our checksum, we notice that block 1 was corrupted. So we fall back to
 block 2 and use the value 9.
 
 Using this concept, the littlefs is able to update metadata blocks atomically.
-There are a few other tweaks, such as using a 32 bit crc and using sequence
+There are a few other tweaks, such as using a 32 bit CRC and using sequence
 arithmetic to handle revision count overflow, but the basic concept
 is the same. These metadata pairs define the backbone of the littlefs, and the
 rest of the filesystem is built on top of these atomic updates.
@@ -184,7 +186,7 @@ Here is what updating a one-block file may look like:
             update data in file        update metadata pair
 ```
 
-It doesn't matter if we lose power while writing block 5 with the new data
+It doesn't matter if we lose power while writing new data to block 5,
 because the old data remains unmodified in block 4. This example also
 highlights how the atomic updates of the metadata blocks provide a
 synchronization barrier for the rest of the littlefs.
@@ -206,10 +208,10 @@ files in filesystems. Of these, the littlefs uses a rather unique [COW](https://
 data structure that allows the filesystem to reuse unmodified parts of the
 file without additional metadata pairs.
 
-First, let's consider storing files in a simple linked-list. What happens when
-we append a block? We have to change the last block in the linked-list to point
-to this new block, which means we have to copy out the last block and change
-the second-to-last block and then the third-to-last and so on until we've
+First lets consider storing files in a simple linked-list. What happens when we
+append a block? We have to change the last block in the linked-list to point
+to this new block, which means we have to copy out the last block, and change
+the second-to-last block, and then the third-to-last, and so on until we've
 copied out the entire file.
 
 ```
@@ -239,9 +241,9 @@ Exhibit B: A backwards linked-list
 '--------'  '--------'  '--------'  '--------'  '--------'  '--------'
 ```
 
-However, a backward linked-list does come with a rather glaring problem.
-Iterating over a file _in order_ has a runtime of O(n^2). Gah! A quadratic
-runtime to just _read_ a file? That's awful. Keep in mind reading files are
+However, a backwards linked-list does come with a rather glaring problem.
+Iterating over a file _in order_ has a runtime cost of O(n^2). Gah! A quadratic
+runtime to just _read_ a file? That's awful. Keep in mind reading files is
 usually the most common filesystem operation.
 
 To avoid this problem, the littlefs uses a multilayered linked-list. For
@@ -266,7 +268,7 @@ Exhibit C: A backward CTZ skip-list
 ```
 
 The additional pointers allow us to navigate the data-structure on disk
-much more efficiently than in a single linked-list.
+much more efficiently than in a singly linked-list.
 
 Taking exhibit C, for example, here is the path from data block 5 to data
 block 1. You can see how data block 3 was completely skipped:
@@ -289,15 +291,15 @@ The path to data block 0 is even quicker, requiring only two jumps:
 
 We can find the runtime complexity by looking at the path to any block from
 the block containing the most pointers. Every step along the path divides
-the search space for the block in half. This gives us a runtime of O(logn).
+the search space for the block in half. This gives us a runtime of O(log n).
 To get to the block with the most pointers, we can perform the same steps
-backward, which puts the runtime at O(2logn) = O(logn). The interesting
+backwards, which puts the runtime at O(2 log n) = O(log n). The interesting
 part about this data structure is that this optimal path occurs naturally
 if we greedily choose the pointer that covers the most distance without passing
 our target block.
 
 So now we have a representation of files that can be appended trivially with
-a runtime of O(1) and can be read with a worst case runtime of O(nlogn).
+a runtime of O(1), and can be read with a worst case runtime of O(n log n).
 Given that the the runtime is also divided by the amount of data we can store
 in a block, this is pretty reasonable.
 
@@ -362,7 +364,7 @@ N = file size in bytes
 
 And this works quite well but is not trivial to calculate. This equation
 requires O(n) to compute, which brings the entire runtime of reading a file
-to O(n^2logn). Fortunately, the additional O(n) does not need to touch disk,
+to O(n^2 log n). Fortunately, the additional O(n) does not need to touch disk,
 so it is not completely unreasonable. But if we could solve this equation into
 a form that is easily computable, we can avoid a big slowdown.
 
@@ -379,8 +381,8 @@ unintuitive property:
 ![mindblown](https://latex.codecogs.com/svg.latex?%5Csum_i%5En%5Cleft%28%5Ctext%7Bctz%7D%28i%29&plus;1%5Cright%29%20%3D%202n-%5Ctext%7Bpopcount%7D%28n%29)
 
 where:  
-ctz(i) = the number of trailing bits that are 0 in i  
-popcount(i) = the number of bits that are 1 in i  
+ctz(x) = the number of trailing bits that are 0 in x  
+popcount(x) = the number of bits that are 1 in x  
 
 It's a bit bewildering that these two seemingly unrelated bitwise instructions
 are related by this property. But if we start to dissect this equation, we can
@@ -410,8 +412,7 @@ a bit to avoid integer overflow:
 ![formulaforoff](https://latex.codecogs.com/svg.latex?%5Cmathit%7Boff%7D%20%3D%20N%20-%20%5Cleft%28B-2%5Cfrac%7Bw%7D%7B8%7D%5Cright%29n%20-%20%5Cfrac%7Bw%7D%7B8%7D%5Ctext%7Bpopcount%7D%28n%29)
 
 The solution involves quite a bit of math, but computers are very good at math.
-We can now solve for the block index plus offset while only needed to store the
-file size in O(1).
+Now we can solve for both the block index and offset from the file size in O(1).
 
 Here is what it might look like to update a file stored with a CTZ skip-list:
 ```
@@ -500,6 +501,7 @@ scanned to find the most recent free list, but once the list is found, the
 state of all free blocks becomes known.
 
 However, this approach had several issues:
+
 - There was a lot of nuanced logic for adding blocks to the free list without
   modifying the blocks because the blocks remain active until the metadata is
   updated.
@@ -773,7 +775,7 @@ deorphan step that simply iterates through every directory in the linked-list
 and checks it against every directory entry in the filesystem to see if it
 has a parent. The deorphan step occurs on the first block allocation after
 boot, so orphans should never cause the littlefs to run out of storage
-prematurely. Note that the deorphan step never needs to run in a readonly
+prematurely. Note that the deorphan step never needs to run in a read-only
 filesystem.
 
 ## The move problem
@@ -883,7 +885,7 @@ a power loss will occur during filesystem activity. We still need to handle
 the condition, but runtime during a power loss takes a back seat to the runtime
 during normal operations.
 
-So what littlefs does is unelegantly simple. When littlefs moves a file, it
+So what littlefs does is inelegantly simple. When littlefs moves a file, it
 marks the file as "moving". This is stored as a single bit in the directory
 entry and doesn't take up much space. Then littlefs moves the directory,
 finishing with the complete remove of the "moving" directory entry.
@@ -979,7 +981,7 @@ if it exists elsewhere in the filesystem.
 So now that we have all of the pieces of a filesystem, we can look at a more
 subtle attribute of embedded storage: The wear down of flash blocks.
 
-The first concern for the littlefs is that prefectly valid blocks can suddenly
+The first concern for the littlefs, is that perfectly valid blocks can suddenly
 become unusable. As a nice side-effect of using a COW data-structure for files,
 we can simply move on to a different block when a file write fails. All
 modifications to files are performed in copies, so we will only replace the
@@ -1152,8 +1154,8 @@ develops errors and needs to be moved.
 ## Wear leveling
 
 The second concern for the littlefs is that blocks in the filesystem may wear
-unevenly. In this situation, a filesystem may meet an early demise whe,
-there are no more noncorrupted blocks that aren't in use. It's common to
+unevenly. In this situation, a filesystem may meet an early demise where
+there are no more non-corrupted blocks that aren't in use. It's common to
 have files that were written once and left unmodified, wasting the potential
 erase cycles of the blocks it sits on.
 
@@ -1171,7 +1173,7 @@ of wear leveling:
 
 In littlefs's case, it's possible to use the revision count on metadata pairs
 to approximate the wear of a metadata block. And combined with the COW nature
-of files, littlefs could provide your usually implementation of dynamic wear
+of files, littlefs could provide your usual implementation of dynamic wear
 leveling.
 
 However, the littlefs does not. This is for a few reasons. Most notably, even
@@ -1206,12 +1208,12 @@ So, to summarize:
 1. The littlefs is composed of directory blocks.
 2. Each directory is a linked-list of metadata pairs.
 3. These metadata pairs can be updated atomically by alternating which
-   metadata block is active.
-4. Directory blocks contain either references to other directories or files.
-5. Files are represented by copy-on-write CTZ skip-lists, which support O(1)
-   append and O(nlogn) reading.
+   metadata block is active
+4. Directory blocks contain either references to other directories or files
+5. Files are represented by copy-on-write CTZ skip-lists which support O(1)
+   append and O(n log n) reading
 6. Blocks are allocated by scanning the filesystem for used blocks in a
-   fixed-size lookahead region is that stored in a bit-vector.
+   fixed-size lookahead region that is stored in a bit-vector
 7. To facilitate scanning the filesystem, all directories are part of a
    linked-list that is threaded through the entire filesystem.
 8. If a block develops an error, the littlefs allocates a new block and
diff --git a/features/filesystem/littlefs/littlefs/Makefile b/features/filesystem/littlefs/littlefs/Makefile
index cf978e79293..ee717936bd4 100644
--- a/features/filesystem/littlefs/littlefs/Makefile
+++ b/features/filesystem/littlefs/littlefs/Makefile
@@ -1,8 +1,8 @@
 TARGET = lfs
 
-CC = gcc
-AR = ar
-SIZE = size
+CC ?= gcc
+AR ?= ar
+SIZE ?= size
 
 SRC += $(wildcard *.c emubd/*.c)
 OBJ := $(SRC:.c=.o)
@@ -14,15 +14,15 @@ TEST := $(patsubst tests/%.sh,%,$(wildcard tests/test_*))
 SHELL = /bin/bash -o pipefail
 
 ifdef DEBUG
-CFLAGS += -O0 -g3
+override CFLAGS += -O0 -g3
 else
-CFLAGS += -Os
+override CFLAGS += -Os
 endif
 ifdef WORD
-CFLAGS += -m$(WORD)
+override CFLAGS += -m$(WORD)
 endif
-CFLAGS += -I.
-CFLAGS += -std=c99 -Wall -pedantic
+override CFLAGS += -I.
+override CFLAGS += -std=c99 -Wall -pedantic
 
 
 all: $(TARGET)
@@ -33,11 +33,11 @@ size: $(OBJ)
 	$(SIZE) -t $^
 
 .SUFFIXES:
-test: test_format test_dirs test_files test_seek test_parallel \
+test: test_format test_dirs test_files test_seek test_truncate test_parallel \
 	test_alloc test_paths test_orphan test_move test_corrupt
 test_%: tests/test_%.sh
 ifdef QUIET
-	./$< | sed -n '/^[-=]/p'
+	@./$< | sed -n '/^[-=]/p'
 else
 	./$<
 endif
diff --git a/features/filesystem/littlefs/littlefs/README.md b/features/filesystem/littlefs/littlefs/README.md
index 387e7567708..0512e146f13 100644
--- a/features/filesystem/littlefs/littlefs/README.md
+++ b/features/filesystem/littlefs/littlefs/README.md
@@ -16,7 +16,7 @@ of memory. Recursion is avoided, and dynamic memory is limited to configurable
 buffers that can be provided statically.
 
 **Power-loss resilient** - The littlefs is designed for systems that may have
-random power failures. The littlefs has strong copy-on-write guaruntees, and
+random power failures. The littlefs has strong copy-on-write guarantees, and
 storage on disk is always kept in a valid state.
 
 **Wear leveling** - Because the most common form of embedded storage is erodible
@@ -88,7 +88,7 @@ int main(void) {
 ## Usage
 
 Detailed documentation (or at least as much detail as is currently available)
-can be cound in the comments in [lfs.h](lfs.h).
+can be found in the comments in [lfs.h](lfs.h).
 
 As you may have noticed, littlefs takes in a configuration structure that
 defines how the filesystem operates. The configuration struct provides the
@@ -105,7 +105,7 @@ Once mounted, the littlefs provides a full set of POSIX-like file and
 directory functions, with the deviation that the allocation of filesystem
 structures must be provided by the user.
 
-All POSIX operations, such as remove and rename, are atomic, even in the event
+All POSIX operations, such as remove and rename, are atomic, even in event
 of power loss. Additionally, no file updates are actually committed to the
 filesystem until sync or close is called on the file.
 
@@ -141,8 +141,14 @@ make test
 
 ## Related projects
 
+[Mbed OS](https://github.com/ARMmbed/mbed-os/tree/master/features/filesystem/littlefs) -
+The easiest way to get started with littlefs is to jump into [Mbed](https://os.mbed.com/),
+which already has block device drivers for most forms of embedded storage. The
+littlefs is available in Mbed OS as the [LittleFileSystem](https://os.mbed.com/docs/latest/reference/littlefilesystem.html)
+class.
+
 [littlefs-fuse](https://github.com/geky/littlefs-fuse) - A [FUSE](https://github.com/libfuse/libfuse)
-wrapper for littlefs. The project allows you to mount littlefs directly in a
+wrapper for littlefs. The project allows you to mount littlefs directly on a
 Linux machine. Can be useful for debugging littlefs if you have an SD card
 handy.
 
diff --git a/features/filesystem/littlefs/littlefs/SPEC.md b/features/filesystem/littlefs/littlefs/SPEC.md
index 9f3135b16a3..74611a92818 100644
--- a/features/filesystem/littlefs/littlefs/SPEC.md
+++ b/features/filesystem/littlefs/littlefs/SPEC.md
@@ -46,7 +46,7 @@ Here's the layout of metadata blocks on disk:
 | 0x04   | 32 bits       | dir size       |
 | 0x08   | 64 bits       | tail pointer   |
 | 0x10   | size-16 bytes | dir entries    |
-| 0x00+s | 32 bits       | crc            |
+| 0x00+s | 32 bits       | CRC            |
 
 **Revision count** - Incremented every update, only the uncorrupted
 metadata-block with the most recent revision count contains the valid metadata.
@@ -75,7 +75,7 @@ Here's an example of a simple directory stored on disk:
 (32 bits) revision count = 10                    (0x0000000a)
 (32 bits) dir size       = 154 bytes, end of dir (0x0000009a)
 (64 bits) tail pointer   = 37, 36                (0x00000025, 0x00000024)
-(32 bits) crc            = 0xc86e3106
+(32 bits) CRC            = 0xc86e3106
 
 00000000: 0a 00 00 00 9a 00 00 00 25 00 00 00 24 00 00 00  ........%...$...
 00000010: 22 08 00 03 05 00 00 00 04 00 00 00 74 65 61 22  "...........tea"
@@ -142,8 +142,8 @@ attributes are system specific, there is not much guarantee on the values in
 this section, and systems are expected to work even when it is empty. See the
 [attributes](#entry-attributes) section for more details.
 
-**Name length** - Length of the entry name. Entry names are stored as utf8,
-though most systems will probably only support ascii. Entry names can not
+**Name length** - Length of the entry name. Entry names are stored as UTF8,
+though most systems will probably only support ASCII. Entry names can not
 contain '/' and can not be '.' or '..' because these are a part of the syntax of
 filesystem paths.
 
@@ -222,7 +222,7 @@ Here's an example of a complete superblock:
 (32 bits) block count      = 1024 blocks          (0x00000400)
 (32 bits) version          = 1.1                  (0x00010001)
 (8 bytes) magic string     = littlefs
-(32 bits) crc              = 0xc50b74fa
+(32 bits) CRC              = 0xc50b74fa
 
 00000000: 03 00 00 00 34 00 00 00 03 00 00 00 02 00 00 00  ....4...........
 00000010: 2e 14 00 08 03 00 00 00 02 00 00 00 00 02 00 00  ................
diff --git a/features/filesystem/littlefs/littlefs/emubd/lfs_emubd.c b/features/filesystem/littlefs/littlefs/emubd/lfs_emubd.c
index b87d6deba03..b1595963dd9 100644
--- a/features/filesystem/littlefs/littlefs/emubd/lfs_emubd.c
+++ b/features/filesystem/littlefs/littlefs/emubd/lfs_emubd.c
@@ -190,13 +190,13 @@ int lfs_emubd_erase(const struct lfs_config *cfg, lfs_block_t block) {
     }
 
     if (!err && S_ISREG(st.st_mode) && (S_IWUSR & st.st_mode)) {
-        int err = unlink(emu->path);
+        err = unlink(emu->path);
         if (err) {
             return -errno;
         }
     }
 
-    if (errno == ENOENT || (S_ISREG(st.st_mode) && (S_IWUSR & st.st_mode))) {
+    if (err || (S_ISREG(st.st_mode) && (S_IWUSR & st.st_mode))) {
         FILE *f = fopen(emu->path, "w");
         if (!f) {
             return -errno;
diff --git a/features/filesystem/littlefs/littlefs/lfs.c b/features/filesystem/littlefs/littlefs/lfs.c
index e5cc87434e8..99d21dc5e88 100644
--- a/features/filesystem/littlefs/littlefs/lfs.c
+++ b/features/filesystem/littlefs/littlefs/lfs.c
@@ -18,17 +18,13 @@
 #include "lfs.h"
 #include "lfs_util.h"
 
-#include <string.h>
-#include <stdlib.h>
-#include <assert.h>
-
 
 /// Caching block device operations ///
 static int lfs_cache_read(lfs_t *lfs, lfs_cache_t *rcache,
         const lfs_cache_t *pcache, lfs_block_t block,
         lfs_off_t off, void *buffer, lfs_size_t size) {
     uint8_t *data = buffer;
-    assert(block < lfs->cfg->block_count);
+    LFS_ASSERT(block < lfs->cfg->block_count);
 
     while (size > 0) {
         if (pcache && block == pcache->block && off >= pcache->off &&
@@ -153,7 +149,7 @@ static int lfs_cache_prog(lfs_t *lfs, lfs_cache_t *pcache,
         lfs_cache_t *rcache, lfs_block_t block,
         lfs_off_t off, const void *buffer, lfs_size_t size) {
     const uint8_t *data = buffer;
-    assert(block < lfs->cfg->block_count);
+    LFS_ASSERT(block < lfs->cfg->block_count);
 
     while (size > 0) {
         if (block == pcache->block && off >= pcache->off &&
@@ -180,7 +176,7 @@ static int lfs_cache_prog(lfs_t *lfs, lfs_cache_t *pcache,
 
         // pcache must have been flushed, either by programming and
         // entire block or manually flushing the pcache
-        assert(pcache->block == 0xffffffff);
+        LFS_ASSERT(pcache->block == 0xffffffff);
 
         if (off % lfs->cfg->prog_size == 0 &&
                 size >= lfs->cfg->prog_size) {
@@ -323,6 +319,48 @@ static void lfs_alloc_ack(lfs_t *lfs) {
 }
 
 
+/// Endian swapping functions ///
+static void lfs_dir_fromle32(struct lfs_disk_dir *d) {
+    d->rev     = lfs_fromle32(d->rev);
+    d->size    = lfs_fromle32(d->size);
+    d->tail[0] = lfs_fromle32(d->tail[0]);
+    d->tail[1] = lfs_fromle32(d->tail[1]);
+}
+
+static void lfs_dir_tole32(struct lfs_disk_dir *d) {
+    d->rev     = lfs_tole32(d->rev);
+    d->size    = lfs_tole32(d->size);
+    d->tail[0] = lfs_tole32(d->tail[0]);
+    d->tail[1] = lfs_tole32(d->tail[1]);
+}
+
+static void lfs_entry_fromle32(struct lfs_disk_entry *d) {
+    d->u.dir[0] = lfs_fromle32(d->u.dir[0]);
+    d->u.dir[1] = lfs_fromle32(d->u.dir[1]);
+}
+
+static void lfs_entry_tole32(struct lfs_disk_entry *d) {
+    d->u.dir[0] = lfs_tole32(d->u.dir[0]);
+    d->u.dir[1] = lfs_tole32(d->u.dir[1]);
+}
+
+static void lfs_superblock_fromle32(struct lfs_disk_superblock *d) {
+    d->root[0]     = lfs_fromle32(d->root[0]);
+    d->root[1]     = lfs_fromle32(d->root[1]);
+    d->block_size  = lfs_fromle32(d->block_size);
+    d->block_count = lfs_fromle32(d->block_count);
+    d->version     = lfs_fromle32(d->version);
+}
+
+static void lfs_superblock_tole32(struct lfs_disk_superblock *d) {
+    d->root[0]     = lfs_tole32(d->root[0]);
+    d->root[1]     = lfs_tole32(d->root[1]);
+    d->block_size  = lfs_tole32(d->block_size);
+    d->block_count = lfs_tole32(d->block_count);
+    d->version     = lfs_tole32(d->version);
+}
+
+
 /// Metadata pair and directory operations ///
 static inline void lfs_pairswap(lfs_block_t pair[2]) {
     lfs_block_t t = pair[0];
@@ -364,6 +402,7 @@ static int lfs_dir_alloc(lfs_t *lfs, lfs_dir_t *dir) {
     // rather than clobbering one of the blocks we just pretend
     // the revision may be valid
     int err = lfs_bd_read(lfs, dir->pair[0], 0, &dir->d.rev, 4);
+    dir->d.rev = lfs_fromle32(dir->d.rev);
     if (err) {
         return err;
     }
@@ -389,6 +428,7 @@ static int lfs_dir_fetch(lfs_t *lfs,
     for (int i = 0; i < 2; i++) {
         struct lfs_disk_dir test;
         int err = lfs_bd_read(lfs, tpair[i], 0, &test, sizeof(test));
+        lfs_dir_fromle32(&test);
         if (err) {
             return err;
         }
@@ -403,7 +443,9 @@ static int lfs_dir_fetch(lfs_t *lfs,
         }
 
         uint32_t crc = 0xffffffff;
+        lfs_dir_tole32(&test);
         lfs_crc(&crc, &test, sizeof(test));
+        lfs_dir_fromle32(&test);
         err = lfs_bd_crc(lfs, tpair[i], sizeof(test),
                 (0x7fffffff & test.size) - sizeof(test), &crc);
         if (err) {
@@ -463,8 +505,10 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
             }
 
             uint32_t crc = 0xffffffff;
+            lfs_dir_tole32(&dir->d);
             lfs_crc(&crc, &dir->d, sizeof(dir->d));
             err = lfs_bd_prog(lfs, dir->pair[0], 0, &dir->d, sizeof(dir->d));
+            lfs_dir_fromle32(&dir->d);
             if (err) {
                 if (err == LFS_ERR_CORRUPT) {
                     goto relocate;
@@ -478,7 +522,7 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
             while (newoff < (0x7fffffff & dir->d.size)-4) {
                 if (i < count && regions[i].oldoff == oldoff) {
                     lfs_crc(&crc, regions[i].newdata, regions[i].newlen);
-                    int err = lfs_bd_prog(lfs, dir->pair[0],
+                    err = lfs_bd_prog(lfs, dir->pair[0],
                             newoff, regions[i].newdata, regions[i].newlen);
                     if (err) {
                         if (err == LFS_ERR_CORRUPT) {
@@ -492,7 +536,7 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
                     i += 1;
                 } else {
                     uint8_t data;
-                    int err = lfs_bd_read(lfs, oldpair[1], oldoff, &data, 1);
+                    err = lfs_bd_read(lfs, oldpair[1], oldoff, &data, 1);
                     if (err) {
                         return err;
                     }
@@ -511,7 +555,9 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
                 }
             }
 
+            crc = lfs_tole32(crc);
             err = lfs_bd_prog(lfs, dir->pair[0], newoff, &crc, 4);
+            crc = lfs_fromle32(crc);
             if (err) {
                 if (err == LFS_ERR_CORRUPT) {
                     goto relocate;
@@ -584,11 +630,14 @@ static int lfs_dir_commit(lfs_t *lfs, lfs_dir_t *dir,
 }
 
 static int lfs_dir_update(lfs_t *lfs, lfs_dir_t *dir,
-        const lfs_entry_t *entry, const void *data) {
-    return lfs_dir_commit(lfs, dir, (struct lfs_region[]){
+        lfs_entry_t *entry, const void *data) {
+    lfs_entry_tole32(&entry->d);
+    int err = lfs_dir_commit(lfs, dir, (struct lfs_region[]){
             {entry->off, sizeof(entry->d), &entry->d, sizeof(entry->d)},
             {entry->off+sizeof(entry->d), entry->d.nlen, data, entry->d.nlen}
         }, data ? 2 : 1);
+    lfs_entry_fromle32(&entry->d);
+    return err;
 }
 
 static int lfs_dir_append(lfs_t *lfs, lfs_dir_t *dir,
@@ -597,10 +646,14 @@ static int lfs_dir_append(lfs_t *lfs, lfs_dir_t *dir,
     while (true) {
         if (dir->d.size + lfs_entry_size(entry) <= lfs->cfg->block_size) {
             entry->off = dir->d.size - 4;
-            return lfs_dir_commit(lfs, dir, (struct lfs_region[]){
+
+            lfs_entry_tole32(&entry->d);
+            int err = lfs_dir_commit(lfs, dir, (struct lfs_region[]){
                     {entry->off, 0, &entry->d, sizeof(entry->d)},
                     {entry->off, 0, data, entry->d.nlen}
                 }, 2);
+            lfs_entry_fromle32(&entry->d);
+            return err;
         }
 
         // we need to allocate a new dir block
@@ -614,10 +667,12 @@ static int lfs_dir_append(lfs_t *lfs, lfs_dir_t *dir,
             newdir.d.tail[0] = dir->d.tail[0];
             newdir.d.tail[1] = dir->d.tail[1];
             entry->off = newdir.d.size - 4;
+            lfs_entry_tole32(&entry->d);
             err = lfs_dir_commit(lfs, &newdir, (struct lfs_region[]){
                     {entry->off, 0, &entry->d, sizeof(entry->d)},
                     {entry->off, 0, data, entry->d.nlen}
                 }, 2);
+            lfs_entry_fromle32(&entry->d);
             if (err) {
                 return err;
             }
@@ -703,6 +758,7 @@ static int lfs_dir_next(lfs_t *lfs, lfs_dir_t *dir, lfs_entry_t *entry) {
 
     int err = lfs_bd_read(lfs, dir->pair[0], dir->off,
             &entry->d, sizeof(entry->d));
+    lfs_entry_fromle32(&entry->d);
     if (err) {
         return err;
     }
@@ -1002,7 +1058,7 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
             return LFS_ERR_INVAL;
         }
 
-        int err = lfs_dir_fetch(lfs, dir, dir->d.tail);
+        err = lfs_dir_fetch(lfs, dir, dir->d.tail);
         if (err) {
             return err;
         }
@@ -1013,6 +1069,7 @@ int lfs_dir_seek(lfs_t *lfs, lfs_dir_t *dir, lfs_off_t off) {
 }
 
 lfs_soff_t lfs_dir_tell(lfs_t *lfs, lfs_dir_t *dir) {
+    (void)lfs;
     return dir->pos;
 }
 
@@ -1064,11 +1121,12 @@ static int lfs_ctz_find(lfs_t *lfs,
                 lfs_ctz(current));
 
         int err = lfs_cache_read(lfs, rcache, pcache, head, 4*skip, &head, 4);
+        head = lfs_fromle32(head);
         if (err) {
             return err;
         }
 
-        assert(head >= 2 && head <= lfs->cfg->block_count);
+        LFS_ASSERT(head >= 2 && head <= lfs->cfg->block_count);
         current -= 1 << skip;
     }
 
@@ -1088,7 +1146,7 @@ static int lfs_ctz_extend(lfs_t *lfs,
         if (err) {
             return err;
         }
-        assert(nblock >= 2 && nblock <= lfs->cfg->block_count);
+        LFS_ASSERT(nblock >= 2 && nblock <= lfs->cfg->block_count);
 
         if (true) {
             err = lfs_bd_erase(lfs, nblock);
@@ -1113,7 +1171,7 @@ static int lfs_ctz_extend(lfs_t *lfs,
             if (size != lfs->cfg->block_size) {
                 for (lfs_off_t i = 0; i < size; i++) {
                     uint8_t data;
-                    int err = lfs_cache_read(lfs, rcache, NULL,
+                    err = lfs_cache_read(lfs, rcache, NULL,
                             head, i, &data, 1);
                     if (err) {
                         return err;
@@ -1139,8 +1197,10 @@ static int lfs_ctz_extend(lfs_t *lfs,
             lfs_size_t skips = lfs_ctz(index) + 1;
 
             for (lfs_off_t i = 0; i < skips; i++) {
-                int err = lfs_cache_prog(lfs, pcache, rcache,
+                head = lfs_tole32(head);
+                err = lfs_cache_prog(lfs, pcache, rcache,
                         nblock, 4*i, &head, 4);
+                head = lfs_fromle32(head);
                 if (err) {
                     if (err == LFS_ERR_CORRUPT) {
                         goto relocate;
@@ -1151,12 +1211,13 @@ static int lfs_ctz_extend(lfs_t *lfs,
                 if (i != skips-1) {
                     err = lfs_cache_read(lfs, rcache, NULL,
                             head, 4*i, &head, 4);
+                    head = lfs_fromle32(head);
                     if (err) {
                         return err;
                     }
                 }
 
-                assert(head >= 2 && head <= lfs->cfg->block_count);
+                LFS_ASSERT(head >= 2 && head <= lfs->cfg->block_count);
             }
 
             *block = nblock;
@@ -1192,12 +1253,24 @@ static int lfs_ctz_traverse(lfs_t *lfs,
             return 0;
         }
 
-        err = lfs_cache_read(lfs, rcache, pcache, head, 0, &head, 4);
+        lfs_block_t heads[2];
+        int count = 2 - (index & 1);
+        err = lfs_cache_read(lfs, rcache, pcache, head, 0, &heads, count*4);
+        heads[0] = lfs_fromle32(heads[0]);
+        heads[1] = lfs_fromle32(heads[1]);
         if (err) {
             return err;
         }
 
-        index -= 1;
+        for (int i = 0; i < count-1; i++) {
+            err = cb(data, heads[i]);
+            if (err) {
+                return err;
+            }
+        }
+
+        head = heads[count-1];
+        index -= count;
     }
 }
 
@@ -1270,12 +1343,12 @@ int lfs_file_open(lfs_t *lfs, lfs_file_t *file,
     if (lfs->cfg->file_buffer) {
         file->cache.buffer = lfs->cfg->file_buffer;
     } else if ((file->flags & 3) == LFS_O_RDONLY) {
-        file->cache.buffer = malloc(lfs->cfg->read_size);
+        file->cache.buffer = lfs_malloc(lfs->cfg->read_size);
         if (!file->cache.buffer) {
             return LFS_ERR_NOMEM;
         }
     } else {
-        file->cache.buffer = malloc(lfs->cfg->prog_size);
+        file->cache.buffer = lfs_malloc(lfs->cfg->prog_size);
         if (!file->cache.buffer) {
             return LFS_ERR_NOMEM;
         }
@@ -1301,7 +1374,7 @@ int lfs_file_close(lfs_t *lfs, lfs_file_t *file) {
 
     // clean up memory
     if (!lfs->cfg->file_buffer) {
-        free(file->cache.buffer);
+        lfs_free(file->cache.buffer);
     }
 
     return err;
@@ -1437,7 +1510,7 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
             !lfs_pairisnull(file->pair)) {
         // update dir entry
         lfs_dir_t cwd;
-        int err = lfs_dir_fetch(lfs, &cwd, file->pair);
+        err = lfs_dir_fetch(lfs, &cwd, file->pair);
         if (err) {
             return err;
         }
@@ -1445,15 +1518,12 @@ int lfs_file_sync(lfs_t *lfs, lfs_file_t *file) {
         lfs_entry_t entry = {.off = file->poff};
         err = lfs_bd_read(lfs, cwd.pair[0], entry.off,
                 &entry.d, sizeof(entry.d));
+        lfs_entry_fromle32(&entry.d);
         if (err) {
             return err;
         }
 
-        if (entry.d.type != LFS_TYPE_REG) {
-            // sanity check valid entry
-            return LFS_ERR_INVAL;
-        }
-
+        LFS_ASSERT(entry.d.type == LFS_TYPE_REG);
         entry.d.u.file.head = file->head;
         entry.d.u.file.size = file->size;
 
@@ -1474,7 +1544,7 @@ lfs_ssize_t lfs_file_read(lfs_t *lfs, lfs_file_t *file,
     lfs_size_t nsize = size;
 
     if ((file->flags & 3) == LFS_O_WRONLY) {
-        return LFS_ERR_INVAL;
+        return LFS_ERR_BADF;
     }
 
     if (file->flags & LFS_F_WRITING) {
@@ -1530,7 +1600,7 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
     lfs_size_t nsize = size;
 
     if ((file->flags & 3) == LFS_O_RDONLY) {
-        return LFS_ERR_INVAL;
+        return LFS_ERR_BADF;
     }
 
     if (file->flags & LFS_F_READING) {
@@ -1651,7 +1721,60 @@ lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
     return file->pos;
 }
 
+int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size) {
+    if ((file->flags & 3) == LFS_O_RDONLY) {
+        return LFS_ERR_BADF;
+    }
+
+    lfs_off_t oldsize = lfs_file_size(lfs, file);
+    if (size < oldsize) {
+        // need to flush since directly changing metadata
+        int err = lfs_file_flush(lfs, file);
+        if (err) {
+            return err;
+        }
+
+        // lookup new head in ctz skip list
+        err = lfs_ctz_find(lfs, &file->cache, NULL,
+                file->head, file->size,
+                size, &file->head, &(lfs_off_t){0});
+        if (err) {
+            return err;
+        }
+
+        file->size = size;
+        file->flags |= LFS_F_DIRTY;
+    } else if (size > oldsize) {
+        lfs_off_t pos = file->pos;
+
+        // flush+seek if not already at end
+        if (file->pos != oldsize) {
+            int err = lfs_file_seek(lfs, file, 0, LFS_SEEK_END);
+            if (err < 0) {
+                return err;
+            }
+        }
+
+        // fill with zeros
+        while (file->pos < size) {
+            lfs_ssize_t res = lfs_file_write(lfs, file, &(uint8_t){0}, 1);
+            if (res < 0) {
+                return res;
+            }
+        }
+
+        // restore pos
+        int err = lfs_file_seek(lfs, file, pos, LFS_SEEK_SET);
+        if (err < 0) {
+            return err;
+        }
+    }
+
+    return 0;
+}
+
 lfs_soff_t lfs_file_tell(lfs_t *lfs, lfs_file_t *file) {
+    (void)lfs;
     return file->pos;
 }
 
@@ -1665,11 +1788,16 @@ int lfs_file_rewind(lfs_t *lfs, lfs_file_t *file) {
 }
 
 lfs_soff_t lfs_file_size(lfs_t *lfs, lfs_file_t *file) {
-    return lfs_max(file->pos, file->size);
+    (void)lfs;
+    if (file->flags & LFS_F_WRITING) {
+        return lfs_max(file->pos, file->size);
+    } else {
+        return file->size;
+    }
 }
 
 
-/// General fs oprations ///
+/// General fs operations ///
 int lfs_stat(lfs_t *lfs, const char *path, struct lfs_info *info) {
     // check for root, can only be something like '/././../.'
     if (strspn(path, "/.") == strlen(path)) {
@@ -1733,11 +1861,11 @@ int lfs_remove(lfs_t *lfs, const char *path) {
         // must be empty before removal, checking size
         // without masking top bit checks for any case where
         // dir is not empty
-        int err = lfs_dir_fetch(lfs, &dir, entry.d.u.dir);
+        err = lfs_dir_fetch(lfs, &dir, entry.d.u.dir);
         if (err) {
             return err;
         } else if (dir.d.size != sizeof(dir.d)+4) {
-            return LFS_ERR_INVAL;
+            return LFS_ERR_NOTEMPTY;
         }
     }
 
@@ -1754,11 +1882,11 @@ int lfs_remove(lfs_t *lfs, const char *path) {
             return res;
         }
 
-        assert(res); // must have pred
+        LFS_ASSERT(res); // must have pred
         cwd.d.tail[0] = dir.d.tail[0];
         cwd.d.tail[1] = dir.d.tail[1];
 
-        int err = lfs_dir_commit(lfs, &cwd, NULL, 0);
+        err = lfs_dir_commit(lfs, &cwd, NULL, 0);
         if (err) {
             return err;
         }
@@ -1807,7 +1935,7 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
 
     // must have same type
     if (prevexists && preventry.d.type != oldentry.d.type) {
-        return LFS_ERR_INVAL;
+        return LFS_ERR_ISDIR;
     }
 
     lfs_dir_t dir;
@@ -1815,11 +1943,11 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
         // must be empty before removal, checking size
         // without masking top bit checks for any case where
         // dir is not empty
-        int err = lfs_dir_fetch(lfs, &dir, preventry.d.u.dir);
+        err = lfs_dir_fetch(lfs, &dir, preventry.d.u.dir);
         if (err) {
             return err;
         } else if (dir.d.size != sizeof(dir.d)+4) {
-            return LFS_ERR_INVAL;
+            return LFS_ERR_NOTEMPTY;
         }
     }
 
@@ -1842,12 +1970,12 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
     newentry.d.nlen = strlen(newpath);
 
     if (prevexists) {
-        int err = lfs_dir_update(lfs, &newcwd, &newentry, newpath);
+        err = lfs_dir_update(lfs, &newcwd, &newentry, newpath);
         if (err) {
             return err;
         }
     } else {
-        int err = lfs_dir_append(lfs, &newcwd, &newentry, newpath);
+        err = lfs_dir_append(lfs, &newcwd, &newentry, newpath);
         if (err) {
             return err;
         }
@@ -1871,11 +1999,11 @@ int lfs_rename(lfs_t *lfs, const char *oldpath, const char *newpath) {
             return res;
         }
 
-        assert(res); // must have pred
+        LFS_ASSERT(res); // must have pred
         newcwd.d.tail[0] = dir.d.tail[0];
         newcwd.d.tail[1] = dir.d.tail[1];
 
-        int err = lfs_dir_commit(lfs, &newcwd, NULL, 0);
+        err = lfs_dir_commit(lfs, &newcwd, NULL, 0);
         if (err) {
             return err;
         }
@@ -1894,7 +2022,7 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
     if (lfs->cfg->read_buffer) {
         lfs->rcache.buffer = lfs->cfg->read_buffer;
     } else {
-        lfs->rcache.buffer = malloc(lfs->cfg->read_size);
+        lfs->rcache.buffer = lfs_malloc(lfs->cfg->read_size);
         if (!lfs->rcache.buffer) {
             return LFS_ERR_NOMEM;
         }
@@ -1905,26 +2033,30 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
     if (lfs->cfg->prog_buffer) {
         lfs->pcache.buffer = lfs->cfg->prog_buffer;
     } else {
-        lfs->pcache.buffer = malloc(lfs->cfg->prog_size);
+        lfs->pcache.buffer = lfs_malloc(lfs->cfg->prog_size);
         if (!lfs->pcache.buffer) {
             return LFS_ERR_NOMEM;
         }
     }
 
     // setup lookahead, round down to nearest 32-bits
-    assert(lfs->cfg->lookahead % 32 == 0);
-    assert(lfs->cfg->lookahead > 0);
+    LFS_ASSERT(lfs->cfg->lookahead % 32 == 0);
+    LFS_ASSERT(lfs->cfg->lookahead > 0);
     if (lfs->cfg->lookahead_buffer) {
         lfs->free.buffer = lfs->cfg->lookahead_buffer;
     } else {
-        lfs->free.buffer = malloc(lfs->cfg->lookahead/8);
+        lfs->free.buffer = lfs_malloc(lfs->cfg->lookahead/8);
         if (!lfs->free.buffer) {
             return LFS_ERR_NOMEM;
         }
     }
 
+    // check that program and read sizes are multiples of the block size
+    LFS_ASSERT(lfs->cfg->prog_size % lfs->cfg->read_size == 0);
+    LFS_ASSERT(lfs->cfg->block_size % lfs->cfg->prog_size == 0);
+
     // check that the block size is large enough to fit ctz pointers
-    assert(4*lfs_npw2(0xffffffff / (lfs->cfg->block_size-2*4))
+    LFS_ASSERT(4*lfs_npw2(0xffffffff / (lfs->cfg->block_size-2*4))
             <= lfs->cfg->block_size);
 
     // setup default state
@@ -1940,15 +2072,15 @@ static int lfs_init(lfs_t *lfs, const struct lfs_config *cfg) {
 static int lfs_deinit(lfs_t *lfs) {
     // free allocated memory
     if (!lfs->cfg->read_buffer) {
-        free(lfs->rcache.buffer);
+        lfs_free(lfs->rcache.buffer);
     }
 
     if (!lfs->cfg->prog_buffer) {
-        free(lfs->pcache.buffer);
+        lfs_free(lfs->pcache.buffer);
     }
 
     if (!lfs->cfg->lookahead_buffer) {
-        free(lfs->free.buffer);
+        lfs_free(lfs->free.buffer);
     }
 
     return 0;
@@ -1995,7 +2127,7 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
         .d.type = LFS_TYPE_SUPERBLOCK,
         .d.elen = sizeof(superblock.d) - sizeof(superblock.d.magic) - 4,
         .d.nlen = sizeof(superblock.d.magic),
-        .d.version = 0x00010001,
+        .d.version = LFS_DISK_VERSION,
         .d.magic = {"littlefs"},
         .d.block_size  = lfs->cfg->block_size,
         .d.block_count = lfs->cfg->block_count,
@@ -2006,9 +2138,10 @@ int lfs_format(lfs_t *lfs, const struct lfs_config *cfg) {
     superdir.d.size = sizeof(superdir.d) + sizeof(superblock.d) + 4;
 
     // write both pairs to be safe
+    lfs_superblock_tole32(&superblock.d);
     bool valid = false;
     for (int i = 0; i < 2; i++) {
-        int err = lfs_dir_commit(lfs, &superdir, (struct lfs_region[]){
+        err = lfs_dir_commit(lfs, &superdir, (struct lfs_region[]){
                 {sizeof(superdir.d), sizeof(superblock.d),
                  &superblock.d, sizeof(superblock.d)}
             }, 1);
@@ -2054,8 +2187,9 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
     }
 
     if (!err) {
-        int err = lfs_bd_read(lfs, dir.pair[0], sizeof(dir.d),
+        err = lfs_bd_read(lfs, dir.pair[0], sizeof(dir.d),
                 &superblock.d, sizeof(superblock.d));
+        lfs_superblock_fromle32(&superblock.d);
         if (err) {
             return err;
         }
@@ -2069,10 +2203,11 @@ int lfs_mount(lfs_t *lfs, const struct lfs_config *cfg) {
         return LFS_ERR_CORRUPT;
     }
 
-    if (superblock.d.version > (0x00010001 | 0x0000ffff)) {
-        LFS_ERROR("Invalid version %ld.%ld",
-                0xffff & (superblock.d.version >> 16),
-                0xffff & (superblock.d.version >> 0));
+    uint16_t major_version = (0xffff & (superblock.d.version >> 16));
+    uint16_t minor_version = (0xffff & (superblock.d.version >>  0));
+    if ((major_version != LFS_DISK_VERSION_MAJOR ||
+         minor_version > LFS_DISK_VERSION_MINOR)) {
+        LFS_ERROR("Invalid version %ld.%ld", major_version, minor_version);
         return LFS_ERR_INVAL;
     }
 
@@ -2110,15 +2245,16 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
 
         // iterate over contents
         while (dir.off + sizeof(entry.d) <= (0x7fffffff & dir.d.size)-4) {
-            int err = lfs_bd_read(lfs, dir.pair[0], dir.off,
+            err = lfs_bd_read(lfs, dir.pair[0], dir.off,
                     &entry.d, sizeof(entry.d));
+            lfs_entry_fromle32(&entry.d);
             if (err) {
                 return err;
             }
 
             dir.off += lfs_entry_size(&entry);
             if ((0x70 & entry.d.type) == (0x70 & LFS_TYPE_REG)) {
-                int err = lfs_ctz_traverse(lfs, &lfs->rcache, NULL,
+                err = lfs_ctz_traverse(lfs, &lfs->rcache, NULL,
                         entry.d.u.file.head, entry.d.u.file.size, cb, data);
                 if (err) {
                     return err;
@@ -2152,7 +2288,7 @@ int lfs_traverse(lfs_t *lfs, int (*cb)(void*, lfs_block_t), void *data) {
             }
         }
     }
-    
+
     return 0;
 }
 
@@ -2172,7 +2308,7 @@ static int lfs_pred(lfs_t *lfs, const lfs_block_t dir[2], lfs_dir_t *pdir) {
             return true;
         }
 
-        int err = lfs_dir_fetch(lfs, pdir, pdir->d.tail);
+        err = lfs_dir_fetch(lfs, pdir, pdir->d.tail);
         if (err) {
             return err;
         }
@@ -2186,7 +2322,7 @@ static int lfs_parent(lfs_t *lfs, const lfs_block_t dir[2],
     if (lfs_pairisnull(lfs->root)) {
         return 0;
     }
-    
+
     parent->d.tail[0] = 0;
     parent->d.tail[1] = 1;
 
@@ -2198,7 +2334,7 @@ static int lfs_parent(lfs_t *lfs, const lfs_block_t dir[2],
         }
 
         while (true) {
-            int err = lfs_dir_next(lfs, parent, entry);
+            err = lfs_dir_next(lfs, parent, entry);
             if (err && err != LFS_ERR_NOENT) {
                 return err;
             }
@@ -2232,13 +2368,13 @@ static int lfs_moved(lfs_t *lfs, const void *e) {
     // iterate over all directory directory entries
     lfs_entry_t entry;
     while (!lfs_pairisnull(cwd.d.tail)) {
-        int err = lfs_dir_fetch(lfs, &cwd, cwd.d.tail);
+        err = lfs_dir_fetch(lfs, &cwd, cwd.d.tail);
         if (err) {
             return err;
         }
 
         while (true) {
-            int err = lfs_dir_next(lfs, &cwd, &entry);
+            err = lfs_dir_next(lfs, &cwd, &entry);
             if (err && err != LFS_ERR_NOENT) {
                 return err;
             }
@@ -2247,7 +2383,7 @@ static int lfs_moved(lfs_t *lfs, const void *e) {
                 break;
             }
 
-            if (!(0x80 & entry.d.type) && 
+            if (!(0x80 & entry.d.type) &&
                  memcmp(&entry.d.u, e, sizeof(entry.d.u)) == 0) {
                 return true;
             }
@@ -2369,7 +2505,7 @@ int lfs_deorphan(lfs_t *lfs) {
         // check entries for moves
         lfs_entry_t entry;
         while (true) {
-            int err = lfs_dir_next(lfs, &cwd, &entry);
+            err = lfs_dir_next(lfs, &cwd, &entry);
             if (err && err != LFS_ERR_NOENT) {
                 return err;
             }
@@ -2388,7 +2524,7 @@ int lfs_deorphan(lfs_t *lfs) {
                 if (moved) {
                     LFS_DEBUG("Found move %ld %ld",
                             entry.d.u.dir[0], entry.d.u.dir[1]);
-                    int err = lfs_dir_remove(lfs, &cwd, &entry);
+                    err = lfs_dir_remove(lfs, &cwd, &entry);
                     if (err) {
                         return err;
                     }
@@ -2396,7 +2532,7 @@ int lfs_deorphan(lfs_t *lfs) {
                     LFS_DEBUG("Found partial move %ld %ld",
                             entry.d.u.dir[0], entry.d.u.dir[1]);
                     entry.d.type &= ~0x80;
-                    int err = lfs_dir_update(lfs, &cwd, &entry, NULL);
+                    err = lfs_dir_update(lfs, &cwd, &entry, NULL);
                     if (err) {
                         return err;
                     }
diff --git a/features/filesystem/littlefs/littlefs/lfs.h b/features/filesystem/littlefs/littlefs/lfs.h
index 7ac660d4c13..ad379852b71 100644
--- a/features/filesystem/littlefs/littlefs/lfs.h
+++ b/features/filesystem/littlefs/littlefs/lfs.h
@@ -22,6 +22,23 @@
 #include <stdbool.h>
 
 
+/// Version info ///
+
+// Software library version
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS_VERSION 0x00010003
+#define LFS_VERSION_MAJOR (0xffff & (LFS_VERSION >> 16))
+#define LFS_VERSION_MINOR (0xffff & (LFS_VERSION >>  0))
+
+// Version of On-disk data structures
+// Major (top-nibble), incremented on backwards incompatible changes
+// Minor (bottom-nibble), incremented on feature additions
+#define LFS_DISK_VERSION 0x00010001
+#define LFS_DISK_VERSION_MAJOR (0xffff & (LFS_DISK_VERSION >> 16))
+#define LFS_DISK_VERSION_MINOR (0xffff & (LFS_DISK_VERSION >>  0))
+
+
 /// Definitions ///
 
 // Type definitions
@@ -41,16 +58,18 @@ typedef uint32_t lfs_block_t;
 // Possible error codes, these are negative to allow
 // valid positive return values
 enum lfs_error {
-    LFS_ERR_OK      = 0,    // No error
-    LFS_ERR_IO      = -5,   // Error during device operation
-    LFS_ERR_CORRUPT = -52,  // Corrupted
-    LFS_ERR_NOENT   = -2,   // No directory entry
-    LFS_ERR_EXIST   = -17,  // Entry already exists
-    LFS_ERR_NOTDIR  = -20,  // Entry is not a dir
-    LFS_ERR_ISDIR   = -21,  // Entry is a dir
-    LFS_ERR_INVAL   = -22,  // Invalid parameter
-    LFS_ERR_NOSPC   = -28,  // No space left on device
-    LFS_ERR_NOMEM   = -12,  // No more memory available
+    LFS_ERR_OK       = 0,    // No error
+    LFS_ERR_IO       = -5,   // Error during device operation
+    LFS_ERR_CORRUPT  = -52,  // Corrupted
+    LFS_ERR_NOENT    = -2,   // No directory entry
+    LFS_ERR_EXIST    = -17,  // Entry already exists
+    LFS_ERR_NOTDIR   = -20,  // Entry is not a dir
+    LFS_ERR_ISDIR    = -21,  // Entry is a dir
+    LFS_ERR_NOTEMPTY = -39,  // Dir is not empty
+    LFS_ERR_BADF     = -9,   // Bad file number
+    LFS_ERR_INVAL    = -22,  // Invalid parameter
+    LFS_ERR_NOSPC    = -28,  // No space left on device
+    LFS_ERR_NOMEM    = -12,  // No more memory available
 };
 
 // File types
@@ -99,14 +118,14 @@ struct lfs_config {
 
     // Program a region in a block. The block must have previously
     // been erased. Negative error codes are propogated to the user.
-    // The prog function must return LFS_ERR_CORRUPT if the block should
-    // be considered bad.
+    // May return LFS_ERR_CORRUPT if the block should be considered bad.
     int (*prog)(const struct lfs_config *c, lfs_block_t block,
             lfs_off_t off, const void *buffer, lfs_size_t size);
 
     // Erase a block. A block must be erased before being programmed.
     // The state of an erased block is undefined. Negative error codes
     // are propogated to the user.
+    // May return LFS_ERR_CORRUPT if the block should be considered bad.
     int (*erase)(const struct lfs_config *c, lfs_block_t block);
 
     // Sync the state of the underlying block device. Negative error codes
@@ -121,11 +140,13 @@ struct lfs_config {
     // Minimum size of a block program. This determines the size of program
     // buffers. This may be larger than the physical program size to improve
     // performance by caching more of the block device.
+    // Must be a multiple of the read size.
     lfs_size_t prog_size;
 
     // Size of an erasable block. This does not impact ram consumption and
     // may be larger than the physical erase size. However, this should be
-    // kept small as each file currently takes up an entire block .
+    // kept small as each file currently takes up an entire block.
+    // Must be a multiple of the program size.
     lfs_size_t block_size;
 
     // Number of erasable blocks on the device.
@@ -362,6 +383,11 @@ lfs_ssize_t lfs_file_write(lfs_t *lfs, lfs_file_t *file,
 lfs_soff_t lfs_file_seek(lfs_t *lfs, lfs_file_t *file,
         lfs_soff_t off, int whence);
 
+// Truncates the size of the file to the specified size
+//
+// Returns a negative error code on failure.
+int lfs_file_truncate(lfs_t *lfs, lfs_file_t *file, lfs_off_t size);
+
 // Return the position of the file
 //
 // Equivalent to lfs_file_seek(lfs, file, 0, LFS_SEEK_CUR)
diff --git a/features/filesystem/littlefs/littlefs/lfs_util.h b/features/filesystem/littlefs/littlefs/lfs_util.h
index 17cd5f27851..e70e96ce443 100644
--- a/features/filesystem/littlefs/littlefs/lfs_util.h
+++ b/features/filesystem/littlefs/littlefs/lfs_util.h
@@ -18,16 +18,85 @@
 #ifndef LFS_UTIL_H
 #define LFS_UTIL_H
 
-#include <stdlib.h>
 #include <stdint.h>
+#include <stdbool.h>
+#include <string.h>
+
+#ifndef LFS_NO_MALLOC
+#include <stdlib.h>
+#endif
+#ifndef LFS_NO_ASSERT
+#include <assert.h>
+#endif
+#if !defined(LFS_NO_INFO) || !defined(LFS_NO_DEBUG) || !defined(LFS_NO_WARN) || !defined(LFS_NO_ERROR)
 #include <stdio.h>
-#ifdef __ICCARM__
-#include <intrinsics.h>
 #endif
 
 
-// Builtin functions, these may be replaced by more
-// efficient implementations in the system
+// Macros, may be replaced by system specific wrappers. Arguments to these
+// macros must not have side-effects as the macros can be removed for a smaller
+// code footprint
+
+#ifdef __MBED__
+#include "mbed_debug.h"
+#include "mbed_assert.h"
+#else
+#define MBED_LFS_ENABLE_INFO   false
+#define MBED_LFS_ENABLE_DEBUG  true
+#define MBED_LFS_ENABLE_WARN   true
+#define MBED_LFS_ENABLE_ERROR  true
+#define MBED_LFS_ENABLE_ASSERT true
+#define MBED_LFS_INTRINSICS    true
+#endif
+
+// Logging functions
+#if !defined(LFS_NO_INFO) && MBED_LFS_ENABLE_INFO
+#define LFS_INFO(fmt, ...)  printf("lfs info:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#elif !defined(LFS_NO_INFO) && !defined(MBED_LFS_ENABLE_INFO)
+#define LFS_INFO(fmt, ...)  debug("lfs info:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS_INFO(fmt, ...)
+#endif
+
+#if !defined(LFS_NO_DEBUG) && MBED_LFS_ENABLE_DEBUG
+#define LFS_DEBUG(fmt, ...) printf("lfs debug:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#elif !defined(LFS_NO_DEBUG) && !defined(MBED_LFS_ENABLE_DEBUG)
+#define LFS_DEBUG(fmt, ...) debug("lfs debug:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS_DEBUG(fmt, ...)
+#endif
+
+#if !defined(LFS_NO_WARN) && MBED_LFS_ENABLE_WARN
+#define LFS_WARN(fmt, ...)  printf("lfs warn:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#elif !defined(LFS_NO_WARN) && !defined(MBED_LFS_ENABLE_WARN)
+#define LFS_WARN(fmt, ...)  debug("lfs warn:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS_WARN(fmt, ...)
+#endif
+
+#if !defined(LFS_NO_ERROR) && MBED_LFS_ENABLE_ERROR
+#define LFS_ERROR(fmt, ...) printf("lfs error:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#elif !defined(LFS_NO_ERROR) && !defined(MBED_LFS_ENABLE_ERROR)
+#define LFS_ERROR(fmt, ...) debug("lfs error:%d: " fmt "\n", __LINE__, __VA_ARGS__)
+#else
+#define LFS_ERROR(fmt, ...)
+#endif
+
+// Runtime assertions
+#if !defined(LFS_NO_ASSERT) && MBED_LFS_ENABLE_ASSERT
+#define LFS_ASSERT(test) assert(test)
+#elif !defined(LFS_NO_ASSERT) && !defined(MBED_LFS_ENABLE_ASSERT)
+#define LFS_ASSERT(test) MBED_ASSERT(test)
+#else
+#define LFS_ASSERT(test)
+#endif
+
+
+// Builtin functions, these may be replaced by more efficient
+// toolchain-specific implementations. LFS_NO_INTRINSICS falls back to a more
+// expensive basic C implementation for debugging purposes
+
+// Min/max functions for unsigned 32-bit numbers
 static inline uint32_t lfs_max(uint32_t a, uint32_t b) {
     return (a > b) ? a : b;
 }
@@ -36,42 +105,38 @@ static inline uint32_t lfs_min(uint32_t a, uint32_t b) {
     return (a < b) ? a : b;
 }
 
-static inline uint32_t lfs_ctz(uint32_t a) {
-#if defined(__GNUC__) || defined(__CC_ARM)
-    return __builtin_ctz(a);
-#elif defined(__ICCARM__) && defined(__CLZ)
-    return __CLZ(__RBIT(a));
-#else
-    uint32_t r = 32;
-    a &= -a;
-    if (a) r -= 1;
-    if (a & 0x0000ffff) r -= 16;
-    if (a & 0x00ff00ff) r -= 8;
-    if (a & 0x0f0f0f0f) r -= 4;
-    if (a & 0x33333333) r -= 2;
-    if (a & 0x55555555) r -= 1;
-    return r;
-#endif
-}
-
+// Find the next smallest power of 2 less than or equal to a
 static inline uint32_t lfs_npw2(uint32_t a) {
-#if defined(__GNUC__) || defined(__CC_ARM)
+#if !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && \
+    (defined(__GNUC__) || defined(__CC_ARM))
     return 32 - __builtin_clz(a-1);
-#elif defined(__ICCARM__) && defined(__CLZ)
-    return 32 - __CLZ(a-1);
 #else
     uint32_t r = 0;
     uint32_t s;
+    a -= 1;
     s = (a > 0xffff) << 4; a >>= s; r |= s;
     s = (a > 0xff  ) << 3; a >>= s; r |= s;
     s = (a > 0xf   ) << 2; a >>= s; r |= s;
     s = (a > 0x3   ) << 1; a >>= s; r |= s;
-    return r | (a >> 1);
+    return (r | (a >> 1)) + 1;
+#endif
+}
+
+// Count the number of trailing binary zeros in a
+// lfs_ctz(0) may be undefined
+static inline uint32_t lfs_ctz(uint32_t a) {
+#if !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && \
+    defined(__GNUC__)
+    return __builtin_ctz(a);
+#else
+    return lfs_npw2((a & -a) + 1) - 1;
 #endif
 }
 
+// Count the number of binary ones in a
 static inline uint32_t lfs_popc(uint32_t a) {
-#if defined(__GNUC__) || defined(__CC_ARM)
+#if !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && \
+    (defined(__GNUC__) || defined(__CC_ARM))
     return __builtin_popcount(a);
 #else
     a = a - ((a >> 1) & 0x55555555);
@@ -80,55 +145,55 @@ static inline uint32_t lfs_popc(uint32_t a) {
 #endif
 }
 
+// Find the sequence comparison of a and b, this is the distance
+// between a and b ignoring overflow
 static inline int lfs_scmp(uint32_t a, uint32_t b) {
     return (int)(unsigned)(a - b);
 }
 
-// CRC-32 with polynomial = 0x04c11db7
-void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
-
-
-// Logging functions
-#ifdef __MBED__
-#include "mbed_debug.h"
+// Convert from 32-bit little-endian to native order
+static inline uint32_t lfs_fromle32(uint32_t a) {
+#if !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && ( \
+    (defined(  BYTE_ORDER  ) &&   BYTE_ORDER   ==   ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && __BYTE_ORDER   == __ORDER_LITTLE_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__))
+    return a;
+#elif !defined(LFS_NO_INTRINSICS) && MBED_LFS_INTRINSICS && ( \
+    (defined(  BYTE_ORDER  ) &&   BYTE_ORDER   ==   ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER  ) && __BYTE_ORDER   == __ORDER_BIG_ENDIAN  ) || \
+    (defined(__BYTE_ORDER__) && __BYTE_ORDER__ == __ORDER_BIG_ENDIAN__))
+    return __builtin_bswap32(a);
 #else
-#define MBED_LFS_ENABLE_INFO  false
-#define MBED_LFS_ENABLE_DEBUG true
-#define MBED_LFS_ENABLE_WARN  true
-#define MBED_LFS_ENABLE_ERROR true
+    return (((uint8_t*)&a)[0] <<  0) |
+           (((uint8_t*)&a)[1] <<  8) |
+           (((uint8_t*)&a)[2] << 16) |
+           (((uint8_t*)&a)[3] << 24);
 #endif
+}
 
-#if MBED_LFS_ENABLE_INFO
-#define LFS_INFO(fmt, ...)  printf("lfs info: " fmt "\n", __VA_ARGS__)
-#elif !defined(MBED_LFS_ENABLE_INFO)
-#define LFS_INFO(fmt, ...)  debug("lfs info: " fmt "\n", __VA_ARGS__)
-#else
-#define LFS_INFO(fmt, ...)
-#endif
+// Convert to 32-bit little-endian from native order
+static inline uint32_t lfs_tole32(uint32_t a) {
+    return lfs_fromle32(a);
+}
 
-#if MBED_LFS_ENABLE_DEBUG
-#define LFS_DEBUG(fmt, ...)  printf("lfs debug: " fmt "\n", __VA_ARGS__)
-#elif !defined(MBED_LFS_ENABLE_DEBUG)
-#define LFS_DEBUG(fmt, ...)  debug("lfs debug: " fmt "\n", __VA_ARGS__)
-#else
-#define LFS_DEBUG(fmt, ...)
-#endif
+// Calculate CRC-32 with polynomial = 0x04c11db7
+void lfs_crc(uint32_t *crc, const void *buffer, size_t size);
 
-#if MBED_LFS_ENABLE_WARN
-#define LFS_WARN(fmt, ...)  printf("lfs warn: " fmt "\n", __VA_ARGS__)
-#elif !defined(MBED_LFS_ENABLE_WARN)
-#define LFS_WARN(fmt, ...)  debug("lfs warn: " fmt "\n", __VA_ARGS__)
+// Allocate memory, only used if buffers are not provided to littlefs
+static inline void *lfs_malloc(size_t size) {
+#ifndef LFS_NO_MALLOC
+    return malloc(size);
 #else
-#define LFS_WARN(fmt, ...)
+    return NULL;
 #endif
+}
 
-#if MBED_LFS_ENABLE_ERROR
-#define LFS_ERROR(fmt, ...)  printf("lfs error: " fmt "\n", __VA_ARGS__)
-#elif !defined(MBED_LFS_ENABLE_ERROR)
-#define LFS_ERROR(fmt, ...)  debug("lfs error: " fmt "\n", __VA_ARGS__)
-#else
-#define LFS_ERROR(fmt, ...)
+// Deallocate memory, only used if buffers are not provided to littlefs
+static inline void lfs_free(void *p) {
+#ifndef LFS_NO_MALLOC
+    free(p);
 #endif
+}
 
 
 #endif
diff --git a/features/filesystem/littlefs/littlefs/tests/template.fmt b/features/filesystem/littlefs/littlefs/tests/template.fmt
index 85f00bdd33a..a53f0c7e24e 100644
--- a/features/filesystem/littlefs/littlefs/tests/template.fmt
+++ b/features/filesystem/littlefs/littlefs/tests/template.fmt
@@ -7,11 +7,11 @@
 
 
 // test stuff
-void test_log(const char *s, uintmax_t v) {{
+static void test_log(const char *s, uintmax_t v) {{
     printf("%s: %jd\n", s, v);
 }}
 
-void test_assert(const char *file, unsigned line,
+static void test_assert(const char *file, unsigned line,
         const char *s, uintmax_t v, uintmax_t e) {{
     static const char *last[6] = {{0, 0}};
     if (v != e || !(last[0] == s || last[1] == s ||
@@ -37,7 +37,8 @@ void test_assert(const char *file, unsigned line,
 
 
 // utility functions for traversals
-int test_count(void *p, lfs_block_t b) {{
+static int __attribute__((used)) test_count(void *p, lfs_block_t b) {{
+    (void)b;
     unsigned *u = (unsigned*)p;
     *u += 1;
     return 0;
@@ -58,7 +59,7 @@ lfs_size_t size;
 lfs_size_t wsize;
 lfs_size_t rsize;
 
-uintmax_t res;
+uintmax_t test;
 
 #ifndef LFS_READ_SIZE
 #define LFS_READ_SIZE 16
@@ -96,7 +97,7 @@ const struct lfs_config cfg = {{
 
 
 // Entry point
-int main() {{
+int main(void) {{
     lfs_emubd_create(&cfg, "blocks");
 
 {tests}
diff --git a/features/filesystem/littlefs/littlefs/tests/test.py b/features/filesystem/littlefs/littlefs/tests/test.py
index aa125c7c2fd..24b0d1a37b6 100755
--- a/features/filesystem/littlefs/littlefs/tests/test.py
+++ b/features/filesystem/littlefs/littlefs/tests/test.py
@@ -14,22 +14,34 @@ def generate(test):
         match = re.match('(?: *\n)*( *)(.*)=>(.*);', line, re.DOTALL | re.MULTILINE)
         if match:
             tab, test, expect = match.groups()
-            lines.append(tab+'res = {test};'.format(test=test.strip()))
-            lines.append(tab+'test_assert("{name}", res, {expect});'.format(
+            lines.append(tab+'test = {test};'.format(test=test.strip()))
+            lines.append(tab+'test_assert("{name}", test, {expect});'.format(
                     name = re.match('\w*', test.strip()).group(),
                     expect = expect.strip()))
         else:
             lines.append(line)
 
+    # Create test file
     with open('test.c', 'w') as file:
         file.write(template.format(tests='\n'.join(lines)))
 
+    # Remove build artifacts to force rebuild
+    try:
+        os.remove('test.o')
+        os.remove('lfs')
+    except OSError:
+        pass
+
 def compile():
-    os.environ['CFLAGS'] = os.environ.get('CFLAGS', '') + ' -Werror'
-    subprocess.check_call(['make', '--no-print-directory', '-s'], env=os.environ)
+    subprocess.check_call([
+            os.environ.get('MAKE', 'make'),
+            '--no-print-directory', '-s'])
 
 def execute():
-    subprocess.check_call(["./lfs"])
+    if 'EXEC' in os.environ:
+        subprocess.check_call([os.environ['EXEC'], "./lfs"])
+    else:
+        subprocess.check_call(["./lfs"])
 
 def main(test=None):
     if test and not test.startswith('-'):
diff --git a/features/filesystem/littlefs/littlefs/tests/test_dirs.sh b/features/filesystem/littlefs/littlefs/tests/test_dirs.sh
index 431889007a6..9f9733dd712 100755
--- a/features/filesystem/littlefs/littlefs/tests/test_dirs.sh
+++ b/features/filesystem/littlefs/littlefs/tests/test_dirs.sh
@@ -126,7 +126,7 @@ TEST
 echo "--- Directory remove ---"
 tests/test.py << TEST
     lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "potato") => LFS_ERR_INVAL;
+    lfs_remove(&lfs, "potato") => LFS_ERR_NOTEMPTY;
     lfs_remove(&lfs, "potato/sweet") => 0;
     lfs_remove(&lfs, "potato/baked") => 0;
     lfs_remove(&lfs, "potato/fried") => 0;
@@ -220,7 +220,7 @@ tests/test.py << TEST
     lfs_mount(&lfs, &cfg) => 0;
     lfs_mkdir(&lfs, "warmpotato") => 0;
     lfs_mkdir(&lfs, "warmpotato/mushy") => 0;
-    lfs_rename(&lfs, "hotpotato", "warmpotato") => LFS_ERR_INVAL;
+    lfs_rename(&lfs, "hotpotato", "warmpotato") => LFS_ERR_NOTEMPTY;
 
     lfs_remove(&lfs, "warmpotato/mushy") => 0;
     lfs_rename(&lfs, "hotpotato", "warmpotato") => 0;
@@ -255,7 +255,7 @@ tests/test.py << TEST
     lfs_rename(&lfs, "warmpotato/baked", "coldpotato/baked") => 0;
     lfs_rename(&lfs, "warmpotato/sweet", "coldpotato/sweet") => 0;
     lfs_rename(&lfs, "warmpotato/fried", "coldpotato/fried") => 0;
-    lfs_remove(&lfs, "coldpotato") => LFS_ERR_INVAL;
+    lfs_remove(&lfs, "coldpotato") => LFS_ERR_NOTEMPTY;
     lfs_remove(&lfs, "warmpotato") => 0;
     lfs_unmount(&lfs) => 0;
 TEST
@@ -285,7 +285,7 @@ TEST
 echo "--- Recursive remove ---"
 tests/test.py << TEST
     lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "coldpotato") => LFS_ERR_INVAL;
+    lfs_remove(&lfs, "coldpotato") => LFS_ERR_NOTEMPTY;
 
     lfs_dir_open(&lfs, &dir[0], "coldpotato") => 0;
     lfs_dir_read(&lfs, &dir[0], &info) => 1;
@@ -328,7 +328,7 @@ TEST
 echo "--- Multi-block remove ---"
 tests/test.py << TEST
     lfs_mount(&lfs, &cfg) => 0;
-    lfs_remove(&lfs, "cactus") => LFS_ERR_INVAL;
+    lfs_remove(&lfs, "cactus") => LFS_ERR_NOTEMPTY;
 
     for (int i = 0; i < $LARGESIZE; i++) {
         sprintf((char*)buffer, "cactus/test%d", i);
diff --git a/features/filesystem/littlefs/littlefs/tests/test_truncate.sh b/features/filesystem/littlefs/littlefs/tests/test_truncate.sh
new file mode 100755
index 00000000000..da5ccaf033f
--- /dev/null
+++ b/features/filesystem/littlefs/littlefs/tests/test_truncate.sh
@@ -0,0 +1,158 @@
+#!/bin/bash
+set -eu
+
+SMALLSIZE=32
+MEDIUMSIZE=2048
+LARGESIZE=8192
+
+echo "=== Truncate tests ==="
+rm -rf blocks
+tests/test.py << TEST
+    lfs_format(&lfs, &cfg) => 0;
+TEST
+
+truncate_test() {
+STARTSIZES="$1"
+STARTSEEKS="$2"
+HOTSIZES="$3"
+COLDSIZES="$4"
+tests/test.py << TEST
+    static const lfs_off_t startsizes[] = {$STARTSIZES};
+    static const lfs_off_t startseeks[] = {$STARTSEEKS};
+    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
+
+    lfs_mount(&lfs, &cfg) => 0;
+
+    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
+        sprintf((char*)buffer, "hairyhead%d", i);
+        lfs_file_open(&lfs, &file[0], (const char*)buffer,
+                LFS_O_WRONLY | LFS_O_CREAT | LFS_O_TRUNC) => 0;
+
+        strcpy((char*)buffer, "hair");
+        size = strlen((char*)buffer);
+        for (int j = 0; j < startsizes[i]; j += size) {
+            lfs_file_write(&lfs, &file[0], buffer, size) => size;
+        }
+        lfs_file_size(&lfs, &file[0]) => startsizes[i];
+
+        if (startseeks[i] != startsizes[i]) {
+            lfs_file_seek(&lfs, &file[0],
+                    startseeks[i], LFS_SEEK_SET) => startseeks[i];
+        }
+
+        lfs_file_truncate(&lfs, &file[0], hotsizes[i]) => 0;
+        lfs_file_size(&lfs, &file[0]) => hotsizes[i];
+
+        lfs_file_close(&lfs, &file[0]) => 0;
+    }
+
+    lfs_unmount(&lfs) => 0;
+TEST
+tests/test.py << TEST
+    static const lfs_off_t startsizes[] = {$STARTSIZES};
+    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
+    static const lfs_off_t coldsizes[]  = {$COLDSIZES};
+
+    lfs_mount(&lfs, &cfg) => 0;
+
+    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
+        sprintf((char*)buffer, "hairyhead%d", i);
+        lfs_file_open(&lfs, &file[0], (const char*)buffer, LFS_O_RDWR) => 0;
+        lfs_file_size(&lfs, &file[0]) => hotsizes[i];
+
+        size = strlen("hair");
+        int j = 0;
+        for (; j < startsizes[i] && j < hotsizes[i]; j += size) {
+            lfs_file_read(&lfs, &file[0], buffer, size) => size;
+            memcmp(buffer, "hair", size) => 0;
+        }
+
+        for (; j < hotsizes[i]; j += size) {
+            lfs_file_read(&lfs, &file[0], buffer, size) => size;
+            memcmp(buffer, "\0\0\0\0", size) => 0;
+        }
+
+        lfs_file_truncate(&lfs, &file[0], coldsizes[i]) => 0;
+        lfs_file_size(&lfs, &file[0]) => coldsizes[i];
+
+        lfs_file_close(&lfs, &file[0]) => 0;
+    }
+
+    lfs_unmount(&lfs) => 0;
+TEST
+tests/test.py << TEST
+    static const lfs_off_t startsizes[] = {$STARTSIZES};
+    static const lfs_off_t hotsizes[]   = {$HOTSIZES};
+    static const lfs_off_t coldsizes[]  = {$COLDSIZES};
+
+    lfs_mount(&lfs, &cfg) => 0;
+
+    for (int i = 0; i < sizeof(startsizes)/sizeof(startsizes[0]); i++) {
+        sprintf((char*)buffer, "hairyhead%d", i);
+        lfs_file_open(&lfs, &file[0], (const char*)buffer, LFS_O_RDONLY) => 0;
+        lfs_file_size(&lfs, &file[0]) => coldsizes[i];
+
+        size = strlen("hair");
+        int j = 0;
+        for (; j < startsizes[i] && j < hotsizes[i] && j < coldsizes[i];
+                j += size) {
+            lfs_file_read(&lfs, &file[0], buffer, size) => size;
+            memcmp(buffer, "hair", size) => 0;
+        }
+
+        for (; j < coldsizes[i]; j += size) {
+            lfs_file_read(&lfs, &file[0], buffer, size) => size;
+            memcmp(buffer, "\0\0\0\0", size) => 0;
+        }
+
+        lfs_file_close(&lfs, &file[0]) => 0;
+    }
+
+    lfs_unmount(&lfs) => 0;
+TEST
+}
+
+echo "--- Cold shrinking truncate ---"
+truncate_test \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE"
+
+echo "--- Cold expanding truncate ---"
+truncate_test \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
+
+echo "--- Warm shrinking truncate ---"
+truncate_test \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,            0,            0,            0,            0"
+
+echo "--- Warm expanding truncate ---"
+truncate_test \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
+
+echo "--- Mid-file shrinking truncate ---"
+truncate_test \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "  $LARGESIZE,   $LARGESIZE,   $LARGESIZE,   $LARGESIZE,   $LARGESIZE" \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,            0,            0,            0,            0"
+
+echo "--- Mid-file expanding truncate ---"
+truncate_test \
+    "           0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE, 2*$LARGESIZE" \
+    "           0,            0,   $SMALLSIZE,  $MEDIUMSIZE,   $LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE" \
+    "2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE, 2*$LARGESIZE"
+
+echo "--- Results ---"
+tests/stats.py
diff --git a/features/filesystem/littlefs/mbed_lib.json b/features/filesystem/littlefs/mbed_lib.json
index bafc549f5c1..2cbbe466b9d 100644
--- a/features/filesystem/littlefs/mbed_lib.json
+++ b/features/filesystem/littlefs/mbed_lib.json
@@ -21,6 +21,11 @@
         "value": 512,
         "help": "Number of blocks to lookahead during block allocation. A larger lookahead reduces the number of passes required to allocate a block. The lookahead buffer requires only 1 bit per block so it can be quite large with little ram impact. Should be a multiple of 32."
     },
+    "intrinsics": {
+        "macro_name": "MBED_LFS_INTRINSICS",
+        "value": true,
+        "help": "Enable intrinsics for bit operations such as ctz, popc, and le32 conversion. Can be disabled to help debug toolchain issues"
+    },
     "enable_info": {
         "macro_name": "MBED_LFS_ENABLE_INFO",
         "value": false,
@@ -40,6 +45,11 @@
         "macro_name": "MBED_LFS_ENABLE_ERROR",
         "value": null,
         "help": "Enables error logging, true = enabled, false = disabled, null = disabled only in release builds"
+    },
+    "enable_assert": {
+        "macro_name": "MBED_LFS_ENABLE_ASSERT",
+        "value": null,
+        "help": "Enables asserts, true = enabled, false = disabled, null = disabled only in release builds"
     }
   }
 }