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fs: add documentation on fallocate hole punching

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This patch simply adds documentation on how to handle the hole punching mode of
fallocate for any filesystem wishing to use it.

Signed-off-by: Josef Bacik <josef@redhat.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Josef Bacik 2011-01-05 15:00:07 -05:00 committed by Al Viro
parent 9ecf639a96
commit 924241575a
1 changed files with 9 additions and 0 deletions
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9
Documentation/filesystems/porting
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@ -385,3 +385,12 @@ Documentation/filesystems/vfs.txt for more details.
on many or all directory inodes on the way down a path walk (to check for
exec permission). These must now be rcu-walk aware (flags & IPERM_RCU). See
Documentation/filesystems/vfs.txt for more details.
--
[mandatory]
In ->fallocate() you must check the mode option passed in. If your
filesystem does not support hole punching (deallocating space in the middle of a
file) you must return -EOPNOTSUPP if FALLOC_FL_PUNCH_HOLE is set in mode.
Currently you can only have FALLOC_FL_PUNCH_HOLE with FALLOC_FL_KEEP_SIZE set,
so the i_size should not change when hole punching, even when puching the end of
a file off.