On Mon, Dec 11, 2023 at 1:49 PM Jan Kara <jack@xxxxxxx> wrote:
>
> On Sun 10-12-23 15:24:00, Amir Goldstein wrote:
> > > > > diff --git a/include/linux/fsnotify.h b/include/linux/fsnotify.h
> > > > > index 0a9d6a8a747a..45e6ecbca057 100644
> > > > > --- a/include/linux/fsnotify.h
> > > > > +++ b/include/linux/fsnotify.h
> > > > > @@ -103,7 +103,8 @@ static inline int fsnotify_file(struct file *file, __u32 mask)
> > > > > /*
> > > > > * fsnotify_file_perm - permission hook before file access
> > > > > */
> > > > > -static inline int fsnotify_file_perm(struct file *file, int perm_mask)
> > > > > +static inline int fsnotify_file_perm(struct file *file, int perm_mask,
> > > > > + const loff_t *ppos, size_t count)
> > > > > {
> > > > > __u32 fsnotify_mask = FS_ACCESS_PERM;
> > > >
> > > > Also why do you actually pass in loff_t * instead of plain loff_t? You
> > > > don't plan to change it, do you?
> > >
> > > No I don't.
> >
> > Please note that the pointer is to const loff_t.
> >
> > >
> > > I used NULL to communicate "no range info" to fanotify.
> > > It is currently only used from iterate_dir(), but filesystems may need to
> > > use that to report other cases of pre-content access with no clear range info.
> >
> > Correction. iterate_dir() is not the only case.
> > The callers that use file_ppos(), namely ksys_{read,write}, do_{readv,writev}()
> > will pass a NULL ppos for an FMODE_STREAM file.
> > The only sane behavior I could come up with for those cases
> > is to not report range_info with the FAN_PRE_ACCESS event.
>
> OK, understood. But isn't anything with len == 0 in fact "no valid range
> provided" case? So we could use that to identify a case where we simply
> don't report any range with the event without a need to pass the pointer?
>
IDK. read(2) and pread(2) with count=0 is a valid use case.
and we have reported FAN_ACCESS_PERM for those 0 length calls so far.
reporting those call with no range would be bad for HSM, because all
HSM can do with these events is to fill the entire file content.
Filling the entire file content is a valid action if the backing file does not
support seek or if it is a directory, but it is not a valid action for
an application
induced pread() with zero length.
Did I misunderstand what you meant?
Thanks,
Amir.
