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[1/3] man2/fallocate.2: document behavior with shared blocks

Message ID 147216758965.32321.5757278057091864768.stgit@birch.djwong.org (mailing list archive)
State New, archived
Headers show

Commit Message

Darrick J. Wong Aug. 25, 2016, 11:26 p.m. UTC 
Add a blurb to the fallocate manpage explaining that the fallocate
command 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>
---
 man2/fallocate.2 |    6 ++++++
 1 file changed, 6 insertions(+)



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diff mbox

Patch

diff --git a/man2/fallocate.2 b/man2/fallocate.2
index 54d6340..e050536 100644
--- a/man2/fallocate.2
+++ b/man2/fallocate.2
@@ -83,6 +83,12 @@  is useful for optimizing append workloads.
 Because allocation is done in block size chunks,
 .BR fallocate ()
 may allocate a larger range of disk space than was specified.
+.PP
+Filesystems which allow files to share the same physical storage may
+employ copy on write to unshare the physical blocks to guarantee that
+subsequent writes will not fail due to lack of disk space.
+If the disk blocks are then re-shared, a subsequent write may still
+fail due to lack of space.
 .SS Deallocating file space
 Specifying the
 .BR FALLOC_FL_PUNCH_HOLE