On 10/18/2016 03:54 AM, Darrick J. Wong wrote:
> Add a blurb to the fallocate manpage explaining that the fallocate
> command with the UNSHARE mode flag may use CoW to unshare blocks to
> guarantee that a disk write won't fail with ENOSPC.
> Signed-off-by: Darrick J. Wong <darrick.w...@oracle.com>
> man2/fallocate.2 | 10 ++++++++++
> 1 file changed, 10 insertions(+)
> diff --git a/man2/fallocate.2 b/man2/fallocate.2
> index 54d6340..3ed1460 100644
> --- a/man2/fallocate.2
> +++ b/man2/fallocate.2
> @@ -79,6 +79,16 @@ but the file size will not be changed even if
> is greater than the file size.
> Preallocating zeroed blocks beyond the end of the file in this manner
> is useful for optimizing append workloads.
> +If the
> +.B FALLOC_FL_UNSHARE
> +flag is specified in
> +.IR mode ,
> +shared file data extents will be made private to the file to guarantee
> +that a subsequent write will not fail due to lack of space.
> +Typically, this will be done by performing a copy-on-write operation on
> +all shared data in the file.
> +This flag may not be supported by all filesystems.
> Because allocation is done in block size chunks,
> .BR fallocate ()
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