On Fri, 07 Aug 2009 23:43:07 +0200
Stefani Seibold <stefani@xxxxxxxxxxx> wrote:
> > > + *ppos += rv;
> > > }
> > > return rv;
> > > }
> >
> > Yes, that's odd.
> >
> > I worry that there might be procfs write handlers which are looking at
> > *ppos and whose behaviour might be altered by this patch.
> >
> > <searches a bit>
> >
> > Look at arch/s390/appldata/appldata_base.c:appldata_timer_handler().
> >
> > static int
> > appldata_timer_handler(ctl_table *ctl, int write, struct file *filp,
> > void __user *buffer, size_t *lenp, loff_t *ppos)
> > {
> > int len;
> > char buf[2];
> >
> > if (!*lenp || *ppos) {
> > *lenp = 0;
> > return 0;
> > }
> >
> >
>
> This function will be handled IMHO by the proc_sys_call_handler which
> has nothing to do with the proc_file_write.
> /proc/sys/... file access should be not touched because there are
> handled differently.
hm, OK, fail.
> > Prior to your change, an application which opened that proc file and
> > repeatedly wrote to the fd would repeatedly start and stop the timer.
> >
> > After your change, the second and successive writes would have no
> > effect unless the application was changed to lseek back to the start of
> > the "file".
> >
> > And that was just the second file I looked at via
> >
> > $EDITOR $(grep -l '[*]ppos' $(grep -rl _proc_ .))
>
> Yes, i think you are right, i have forseen also that there maybe some
> pitfalls. The question is: is there any appplication which will be
> broken by this patch?
There is no way of telling. We have to assume that there will be such
code out there.
> So what is your suggestion? Should we drop this patch or should we
> analyze the users and fix it?
Well.
We could review all implementations of ->write_proc. There only seem
to be twenty or so.
If any of them will have their behaviour altered by this patch then
let's look at those on a case-by-case basis and decide whether making
this change will have an acceptable risk.
If we _do_ find one for which we simply cannot make this behavioural
change then.. ugh. We could perhaps add a new `bool
proc_dir_entry.implement_old_broken_behaviour' and set that flag for
the offending driver(s) and test it within proc_write_file().
Or we could do
if (pde->write_proc_new) {
rv = pde->write_proc_new(file, buffer, count, pde->data);
*ppos += rv;
} else {
rv = pde->write_proc(file, buffer, count, pde->data);
}
which is really the same thing and isn't obviously better ;)
> My opinion is to fix it, because it is wrong and it limits the usage of
> the proc_write operation. Many embedded developers like me count on proc
> support, because it is much simpler to use than the seqfile thing.
>
--
To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
