On Fri, 2 Jun 2000, H. Peter Anvin wrote:
> Tigran Aivazian wrote:
> >
> > On 2 Jun 2000, H. Peter Anvin wrote:
> >
> > > Followup to: <Pine.LNX.4.21.0006021321300.2581-100000@saturn.homenet>
> > > By author: Tigran Aivazian <tigran@veritas.com>
> > > In newsgroup: linux.dev.kernel
> > > >
> > > > did you look at kern_mount/umount interface that went into the kernel
> > > > recently? Things like shm and pipefs should (and already are) mounted
> > > > under artificially constructed root mountpoints like "pipe:" which are not
> > > > visible for namelookups coming from userspace. Ok, it is not the case for
> > > > shm currently (it is mounted on /) but perhaps it should be (i.e. the way
> > > > root dentry should be allocated as for pipefs using d_alloc() directly
> > > > instead of using generic d_alloc_root())?
> > > >
> > > > I cc'd Al Viro as I suspect he knows the answer to the above question.
> > > >
> > >
> > > No, shmfs actually needs a real path. Not for SysV IPC, but for POSIX
> > > IPC.
> > >
> >
> > that is not an answer to the question I asked. If you read the sentence
> > that has the question mark (not the subject) you will see that I was
> > asking if the kern_mounted (and not the user-mounted) instance of shmfs
> > has to be mounted under "/" or can it be done like for pipefs under an
> > artificially constructed "shm:" like "pipe:"
> >
>
> Yes, it is.
>
> The distinction you're referring to is the distinction of a real path
> versus a bogus path -- you cannot under any circumstances construct a
> path which uses one of those artificial roots.
>
> POSIX IPC requires a real path. It needs to be in the real namespace,
> which starts with /.
>
ok, I see now - I kind of suspected something like that in my previous
mail before I read this explanation.
Thanks,
Tigran
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