On 06.10.2014 16:12, Jan Kara wrote:
On Fri 03-10-14 10:19:30, Heinrich Schuchardt wrote:
The fanotify and the inotify API can used to monitor changes of the file
system.
System call fallocate modifies files. Hence it should trigger the corresponding
fanotify (FAN_MODIFY) and inotify (IN_MODIFY) events.
This patch adds the missing call to fsnotify_modify.
Well, there are different fallocate() commands and e.g. pure
FALLOC_FL_KEEP_SIZE call will not change any data in the file. I'm not sure
how much we care but I wanted to point that out...
The most interesting case is FALLOC_FL_COLLAPSE_RANGE because this value
allows to create arbitrary file content from random data. Hence I think
we really need to create FAN_MODIFY in this case.
As the fallocate(2) man page teaches:
After a successful call, subsequent writes into the range specified by
offset and len are guaranteed not to fail because of lack of disk space.
So calling fallocate(fd, FALLOC_FL_KEEP_SIZE, offset, len) may result in
different outcomes of a subsequent write depending on the values of
offset and len.
Calling fallocate for a region already zeroed will not result in any
data change.
I would like to compare fallocate() with write().
When we call write() we always create a FAN_MODIFY event even in the
case of overwriting with identical data.
So event FAN_MODIFY does not provide any guarantee that data was
actually changed.
In analogy to write() I suggest to keep the logic for fallocate() as
trivial as possible:
If fallocate() succeeds, create IN_MODIFY and FAN_MODIFY events.
Best regards
Heinrich Schuchardt
Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
---
fs/open.c | 5 +++++
1 file changed, 5 insertions(+)
diff --git a/fs/open.c b/fs/open.c
index d6fd3ac..03aa8e5 100644
--- a/fs/open.c
+++ b/fs/open.c
@@ -295,6 +295,11 @@ int do_fallocate(struct file *file, int mode, loff_t offset, loff_t len)
sb_start_write(inode->i_sb);
ret = file->f_op->fallocate(file, mode, offset, len);
+
+ /* Create inotify and fanotify events. */
+ if (ret == 0)
+ fsnotify_modify(file);
+
sb_end_write(inode->i_sb);
return ret;
}
--
2.1.0
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