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xfs: don't allocate into the data fork for an unshare request

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For an unshare request, we only have to take action if the data fork has
a shared mapping.  We don't care if someone else set up a cow operation.
If we find nothing in the data fork, return a hole to avoid allocating
space.

Note that fallocate will replace the delalloc reservation with an
unwritten extent anyway, so this has no user-visible effects outside of
avoiding unnecessary updates.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>
This commit is contained in:
Darrick J. Wong 2023-05-02 09:14:51 +10:00 committed by Dave Chinner
parent 397b2d7e0f
commit 1f1397b721
1 changed files with 3 additions and 2 deletions
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5
fs/xfs/xfs_iomap.c
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@ -1006,8 +1006,9 @@ xfs_buffered_write_iomap_begin(
if (eof)
imap.br_startoff = end_fsb; /* fake hole until the end */
/* We never need to allocate blocks for zeroing a hole. */
if ((flags & IOMAP_ZERO) && imap.br_startoff > offset_fsb) {
/* We never need to allocate blocks for zeroing or unsharing a hole. */
if ((flags & (IOMAP_UNSHARE | IOMAP_ZERO)) &&
imap.br_startoff > offset_fsb) {
xfs_hole_to_iomap(ip, iomap, offset_fsb, imap.br_startoff);
goto out_unlock;
}