Re: [PATCH 1/1] fallocate: create FAN_MODIFY and IN_MODIFY events

[Heinrich Schuchardt]

Hello Andrew,

the patch in
https://lkml.org/lkml/2014/10/3/56
and cited below was reviewed by Jan Kara.

Please, add it to the MM tree.

Best regards

Heinrich Schuchardt

On 07.10.2014 20:05, Jan Kara wrote:
> On Mon 06-10-14 21:10:25, Heinrich Schuchardt wrote:
> > 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.
>    OK, makes sense. You can add:
> Reviewed-by: Jan Kara <jack@xxxxxxx>
>
> 								Honza
> > > > 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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