cmd/link: fallocate_test.go:46: unexpected disk usage: got 1 blocks, want 2048

[wheelcomplex]

What version of Go are you using (go version)?

$ go version
go version devel +7602d41196 Thu Oct 15 23:12:53 2020 +0000 linux/amd64

Does this issue reproduce with the latest release?

no reproduced in go-1.14.4

What operating system and processor architecture are you using (go env)?

go env Output

$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/home/david/home/.cache/go-build"
GOENV="/home/david/home/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/david/sandspace/pkgextgo/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/david/sandspace/pkgextgo/"
GOPRIVATE=""
GOPROXY="direct"
GOROOT="/home/david/sandspace/go"
GOSUMDB="sum.golang.org"
GOTMPDIR="/home/david/sandspace/tmp"
GOTOOLDIR="/home/david/sandspace/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="0"
GOMOD=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -m64 -fmessage-length=0 -fdebug-prefix-map=/home/david/sandspace/tmp/go-build907894934=/tmp/go-build -gno-record-gcc-switches"

What did you do?

compile Go from source: cd src && ./all.bash

What did you expect to see?

ALL TESTS PASSED

What did you see instead?

ok  	cmd/link/internal/benchmark	0.086s
--- FAIL: TestFallocate (0.00s)
    fallocate_test.go:61: unexpected disk usage: got 1 blocks, want 2048
    fallocate_test.go:61: unexpected disk usage: got 1 blocks, want 4096
    fallocate_test.go:61: unexpected disk usage: got 1 blocks, want 6144
FAIL
FAIL	cmd/link/internal/ld	5.307s

What did you figured out:

openZFS 2.0 reports fallocate is supported, but actaully not.

This should be a bug in openZFS 2.0, but we can workaround.

An improvement for The old issuse will follows up.

[gopherbot]

Change https://golang.org/cl/262837 mentions this issue: cmd/link: TestFallocate fallocate_test error #42005

[toothrot]

/cc @cherrymui @rsc @mdempsky @ianlancetaylor

[cherrymui]

Already commented on the CL.

As @wheelcomplex mentioned, this is an OS bug.

[IvanVolosyuk]

With transparent compression on filesystem level number of blocks can be non-deterministic in this test.

[wheelcomplex]

ZFS 2.0 has released and currently behavior is intended. The CL has been updated to address this.