Messages in this thread Patch in this message | | | Date | Mon, 06 Oct 2014 21:10:25 +0200 | From | Heinrich Schuchardt <> | Subject | Re: [PATCH 1/1] fallocate: create FAN_MODIFY and IN_MODIFY events |
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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@gmx.de> >> --- >> 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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