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Subject[PATCH] xfs: Honor FALLOC_FL_KEEP_SIZE when punching ends of files
Date
Commit 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes") replaced
xfs_zero_remaining_bytes() with calls to iomap helpers.

Unfortunately the new iomap helpers don't enforce that [pos,count) lies
strictly on [0,i_size). This causes fallocate(mode=PUNCH_HOLE|KEEP_SIZE)
calls touching [i_size & ~PAGE_MASK, OFF_T_MAX] to round i_size up to
the nearest multiple of PAGE_SIZE:

calvinow@vm-disks/generic-xfs-1 ~$ dd if=/dev/urandom of=test bs=2048 count=1
calvinow@vm-disks/generic-xfs-1 ~$ stat test
Size: 2048 Blocks: 8 IO Block: 4096 regular file
calvinow@vm-disks/generic-xfs-1 ~$ fallocate -n -l 2048 -o 2048 -p test
calvinow@vm-disks/generic-xfs-1 ~$ stat test
Size: 4096 Blocks: 8 IO Block: 4096 regular file

Fix this by reintroducing the checks xfs_zero_remaining_bytes() did
against i_size into xfs_zero_range().

Reported-by: Aaron Gao <gzh@fb.com>
Fixes: 3c2bdc912a1cc050 ("xfs: kill xfs_zero_remaining_bytes")
Cc: Christoph Hellwig <hch@lst.de>
Cc: <stable@vger.kernel.org> # 4.8+
Signed-off-by: Calvin Owens <calvinowens@fb.com>
---
fs/xfs/xfs_file.c | 11 +++++++++++
1 file changed, 11 insertions(+)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 35703a8..da7cd27 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -58,6 +58,17 @@ xfs_zero_range(
xfs_off_t count,
bool *did_zero)
{
+ /*
+ * Avoid doing I/O beyond eof - it's not necessary
+ * since nothing can read beyond eof. The space will
+ * be zeroed when the file is extended anyway.
+ */
+ if (pos >= XFS_ISIZE(ip))
+ return 0;
+
+ if ((pos + count) >= XFS_ISIZE(ip))
+ count = XFS_ISIZE(ip) - pos - 1;
+
return iomap_zero_range(VFS_I(ip), pos, count, NULL, &xfs_iomap_ops);
}

--
2.9.3
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