xfs: collapse range is delalloc challenged
FSX has been detecting data corruption after to collapse range calls. The key observation is that the offset of the last extent in the file was not being shifted, and hence when the file size was adjusted it was truncating away data because the extents handled been correctly shifted. Tracing indicated that before the collapse, the extent list looked like: .... ino 0x5788 state idx 6 offset 26 block 195904 count 10 flag 0 ino 0x5788 state idx 7 offset 39 block 195917 count 35 flag 0 ino 0x5788 state idx 8 offset 86 block 195964 count 32 flag 0 and after the shift of 2 blocks: ino 0x5788 state idx 6 offset 24 block 195904 count 10 flag 0 ino 0x5788 state idx 7 offset 37 block 195917 count 35 flag 0 ino 0x5788 state idx 8 offset 86 block 195964 count 32 flag 0 Note that the last extent did not change offset. After the changing of the file size: ino 0x5788 state idx 6 offset 24 block 195904 count 10 flag 0 ino 0x5788 state idx 7 offset 37 block 195917 count 35 flag 0 ino 0x5788 state idx 8 offset 86 block 195964 count 30 flag 0 You can see that the last extent had it's length truncated, indicating that we've lost data. The reason for this is that the xfs_bmap_shift_extents() loop uses XFS_IFORK_NEXTENTS() to determine how many extents are in the inode. This, unfortunately, doesn't take into account delayed allocation extents - it's a count of physically allocated extents - and hence when the file being collapsed has a delalloc extent like this one does prior to the range being collapsed: .... ino 0x5788 state idx 4 offset 11 block 4503599627239429 count 1 flag 0 .... it gets the count wrong and terminates the shift loop early. Fix it by using the in-memory extent array size that includes delayed allocation extents to determine the number of extents on the inode. Signed-off-by: NDave Chinner <dchinner@redhat.com> Tested-by: NBrian Foster <bfoster@redhat.com> Reviewed-by: NChristoph Hellwig <hch@lst.de> Signed-off-by: NDave Chinner <david@fromorbit.com>
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