On Wed, Aug 24, 2011 at 01:23:28AM -0700, Andrew Morton wrote:
> On Wed, 24 Aug 2011 12:09:24 +0400 Cyrill Gorcunov <gorcunov@xxxxxxxxx> wrote:
>
> > From: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> >
> > This is done to make it possible to distinguish pipes
> > from fifos when opening one via /proc/<pid>/fd/ link.
> >
> > Signed-off-by: Pavel Emelyanov <xemul@xxxxxxxxxxxxx>
> > Reviewed-by: Tejun Heo <tj@xxxxxxxxxx>
> > Acked-by: Serge Hallyn <serge.hallyn@xxxxxxxxxxxxx>
> > Signed-off-by: Cyrill Gorcunov <gorcunov@xxxxxxxxxx>
> > ---
> > fs/pipe.c | 1 +
> > 1 file changed, 1 insertion(+)
> >
> > Any objections to this one? It was a part of a patchset
> > but can be treated independently so I'm re-sending it alone.
> >
> > Index: linux-2.6.git/fs/pipe.c
> > ===================================================================
> > --- linux-2.6.git.orig/fs/pipe.c
> > +++ linux-2.6.git/fs/pipe.c
> > @@ -1254,6 +1254,7 @@ out:
> >
> > static const struct super_operations pipefs_ops = {
> > .destroy_inode = free_inode_nonrcu,
> > + .statfs = simple_statfs,
> > };
> >
> > /*
>
> OK, I give up - how does it work?
>
> <goes off and reads the kernel>
>
> So it appears that the statfs call would previously return -ENOSYS, but
> with this change the statfs will succeed and userspace can then inspect
> f_type. Yes? I will fix your changelog by adding a description along these
> lines.
Yes, it allows to distinguish pipes from anything else. Initially this patch was
a part of early rfc on checkpoint/restore facility (mostly implemented in
userspace). So we need to distinguish somehow pipes when we dump data from
/proc/pid/fd. That's the main reason. BUT since this patch can be used without
any other c/r bits and can be treated separately I've sent it alone without
any mention of c/r at all.
>
> And I'll ask you to fix it further by telling us why we want to do
> this? The kernel has had this issue for a long time - why does it now
> matter?
Cyrill
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