mirror of https://github.com/mkerrisk/man-pages
man2/fallocate.2: Document behavior with shared blocks
Note that FALLOC_FL_UNSHARE may use CoW to unshare blocks to guarantee that a disk write won't fail with ENOSPC. Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
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@ -79,6 +79,16 @@ but the file size will not be changed even if
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is greater than the file size.
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Preallocating zeroed blocks beyond the end of the file in this manner
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is useful for optimizing append workloads.
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If the
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.B FALLOC_FL_UNSHARE
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flag is specified in
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.IR mode ,
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shared file data extents will be made private to the file to guarantee
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that a subsequent write will not fail due to lack of space.
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Typically, this will be done by performing a copy-on-write operation on
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all shared data in the file.
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This flag may not be supported by all filesystems.
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.PP
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Because allocation is done in block size chunks,
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.BR fallocate ()
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