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

[Heinrich Schuchardt]

On 06.10.2014 15:24, Jan Kara wrote:
> On Fri 03-10-14 20:16:30, Heinrich Schuchardt wrote:
> > The fanotify and the inotify API can be used to monitor changes of the file
> > system.
> >
> > System call ftruncate modifies files. Hence it should trigger the corresponding
> > fanotify (FAN_MODIFY) and inotify (IN_MODIFY) events.
>    Hum, I would think that the appropriate event gets generated by
> fsnotify_change() called from notify_change()?
>
> 								Honza

Hello Jan,

thank you for reviewing.

fsnotify_change() calls
fsnotify(inode, mask, inode, FSNOTIFY_EVENT_INODE, NULL, 0);

fsnotify_modify() calls
fsnotify(inode, mask, path, FSNOTIFY_EVENT_PATH, NULL, 0);

Only with FSNOTIFY_EVENT_PATH a mount is determined in fsnotify().

So a FAN_MODIFY event for a mount cannot occur. But I also did not see a 
FAN_MODIFY event when watching a file either.

IN_MODIFY events are actually created.

So would it be better to do the change in do_truncate and replace the 
call to notify_change by a call to fsnotify_modify?

I just had a look at
http://lxr.free-electrons.com/ident?i=notify_change

There seem to be some other usages of notify_change that deserve 
consideration, e.g. in ecryptfs_truncate().

Best regards

Heinrich Schuchardt

> > Signed-off-by: Heinrich Schuchardt <xypron.glpk@xxxxxx>
> > ---
> >   fs/open.c | 2 ++
> >   1 file changed, 2 insertions(+)
> >
> > diff --git a/fs/open.c b/fs/open.c
> > index d6fd3ac..e36f26e 100644
> > --- a/fs/open.c
> > +++ b/fs/open.c
> > @@ -189,6 +189,8 @@ static long do_sys_ftruncate(unsigned int fd, loff_t length, int small)
> >   		error = security_path_truncate(&f.file->f_path);
> >   	if (!error)
> >   		error = do_truncate(dentry, length, ATTR_MTIME|ATTR_CTIME, f.file);
> > +	if (!error)
> > +		fsnotify_modify(f.file);
> >   	sb_end_write(inode->i_sb);
> >   out_putf:
> >   	fdput(f);
> > --
> > 2.1.0

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