io_ompio_file_open: fix offset calculation with SEEK_END

and SEEK_CUR. fixes an issue reported by Wei-keng Liao

Fixes Issue open-mpi#6858

Note, that some manual adjustements were required compared to the commit
on master due to structural differences in ompio between master and 3.x
branches.

(cherry picked from commit 34b06dc)
Signed-off-by: Edgar Gabriel <[email protected]>

Author: edgargabriel

ompi/mca/io/ompio/io_ompio_file_open.c

@@ -392,14 +392,53 @@ int mca_io_ompio_file_sync (ompi_file_t *fh)
     return ret;
 }
 
+static void mca_io_ompio_file_get_eof_offset (mca_io_ompio_file_t *fh,
+                                              OMPI_MPI_OFFSET_TYPE in_offset,
+                                              OMPI_MPI_OFFSET_TYPE *out_offset)
+{
+    /* a file_seek with SEEK_END might require an actual offset that is 
+       not lined up with the end of the file, depending on the file view.
+       This routine determines the closest (smaller or equal) offset to 
+       the provided in_offset value, avoiding gaps in the file view and avoiding to 
+       break up an etype. 
+    */
+    OMPI_MPI_OFFSET_TYPE offset=0, prev_offset=0, start_offset=0;
+    size_t k=0, blocklen=0;
+    size_t index_in_file_view=0;
+
+    in_offset -= fh->f_disp;
+    if ( fh->f_view_size  > 0 ) {
+        /* starting offset of the current copy of the filew view */
+        start_offset = in_offset / fh->f_view_extent;
+        
+        index_in_file_view = 0;
+        /* determine block id that the offset is located in and
+           the starting offset of that block */
+        while ( offset <= in_offset && index_in_file_view < fh->f_iov_count) {
+            prev_offset = offset;
+            offset = start_offset + (OMPI_MPI_OFFSET_TYPE)(intptr_t) fh->f_decoded_iov[index_in_file_view++].iov_base;
+        }
+        
+        offset = prev_offset;
+        blocklen = fh->f_decoded_iov[index_in_file_view-1].iov_len;
+        while (  offset <= in_offset && k <= blocklen )  {
+            prev_offset = offset;
+            offset += fh->f_etype_size;
+            k += fh->f_etype_size;
+        }
+
+        *out_offset = prev_offset;
+    } 
+    return;
+}
 
 int mca_io_ompio_file_seek (ompi_file_t *fh,
                             OMPI_MPI_OFFSET_TYPE off,
                             int whence)
 {
     int ret = OMPI_SUCCESS;
     mca_io_ompio_data_t *data;
-    OMPI_MPI_OFFSET_TYPE offset, temp_offset;
+    OMPI_MPI_OFFSET_TYPE offset, temp_offset, temp_offset2;
 
     data = (mca_io_ompio_data_t *) fh->f_io_selected_data;
 
@@ -414,16 +453,20 @@ int mca_io_ompio_file_seek (ompi_file_t *fh,
         }
         break;
     case MPI_SEEK_CUR:
-        offset += data->ompio_fh.f_position_in_file_view;
-        offset += data->ompio_fh.f_disp;
+        ret = mca_common_ompio_file_get_position (&data->ompio_fh,
+                                                  &temp_offset);
+        offset += temp_offset * data->ompio_fh.f_etype_size;
+
         if (offset < 0) {
             OPAL_THREAD_UNLOCK(&fh->f_mutex);
             return OMPI_ERROR;
         }
         break;
     case MPI_SEEK_END:
         ret = data->ompio_fh.f_fs->fs_file_get_size (&data->ompio_fh,
-                                                     &temp_offset);
+                                                     &temp_offset2);
+        mca_io_ompio_file_get_eof_offset (&data->ompio_fh,
+                                          temp_offset2, &temp_offset);
         offset += temp_offset;
         if (offset < 0 || OMPI_SUCCESS != ret) {
             OPAL_THREAD_UNLOCK(&fh->f_mutex);
@@ -442,6 +485,7 @@ int mca_io_ompio_file_seek (ompi_file_t *fh,
     return ret;
 }
 
+
 int mca_io_ompio_file_get_position (ompi_file_t *fd,
                                     OMPI_MPI_OFFSET_TYPE *offset)
 {