linux-kernel - Re: [PATCH] xenbus: Use proc_create_mount

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Date:   Tue, 30 Aug 2016 10:02:49 -0500
From:   Seth Forshee <seth.forshee@...onical.com>
To:     Juergen Gross <jgross@...e.com>
Cc:     "Eric W. Biederman" <ebiederm@...ssion.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        David Vrabel <david.vrabel@...rix.com>,
        xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xenbus: Use proc_create_mount_point() to create /proc/xen

On Tue, Aug 30, 2016 at 04:48:08PM +0200, Juergen Gross wrote:
> On 29/08/16 17:03, Seth Forshee wrote:
> > Mounting proc in user namespace containers fails if the xenbus
> > filesystem is mounted on /proc/xen because this directory fails
> > the "permanently empty" test. proc_create_mount_point() exists
> > specifically to create such mountpoints in proc but is currently
> > proc-internal. Export this interface to modules, then use it in
> > xenbus when creating /proc/xen.
> > 
> > Signed-off-by: Seth Forshee <seth.forshee@...onical.com>
> > ---
> >  drivers/xen/xenbus/xenbus_probe.c | 2 +-
> >  fs/proc/generic.c                 | 1 +
> >  fs/proc/internal.h                | 1 -
> >  include/linux/proc_fs.h           | 2 ++
> >  4 files changed, 4 insertions(+), 2 deletions(-)
> > 
> > diff --git a/drivers/xen/xenbus/xenbus_probe.c b/drivers/xen/xenbus/xenbus_probe.c
> > index 33a31cfef55d..b5c1dec4a7c2 100644
> > --- a/drivers/xen/xenbus/xenbus_probe.c
> > +++ b/drivers/xen/xenbus/xenbus_probe.c
> > @@ -826,7 +826,7 @@ static int __init xenbus_init(void)
> >  	 * Create xenfs mountpoint in /proc for compatibility with
> >  	 * utilities that expect to find "xenbus" under "/proc/xen".
> >  	 */
> > -	proc_mkdir("xen", NULL);
> > +	proc_create_mount_point("xen");
> >  #endif
> >  
> >  out_error:
> > diff --git a/fs/proc/generic.c b/fs/proc/generic.c
> > index c633476616e0..be014c544d50 100644
> > --- a/fs/proc/generic.c
> > +++ b/fs/proc/generic.c
> > @@ -477,6 +477,7 @@ struct proc_dir_entry *proc_create_mount_point(const char *name)
> >  	}
> >  	return ent;
> >  }
> > +EXPORT_SYMBOL(proc_create_mount_point);
> 
> EXPORT_SYMBOL_GPL()?

Other similar sorts of calls in proc (proc_mkdir in particular) are
EXPORT_SYMBOL, so I guessed this one should follow suit. But if it
should be EXPORT_SYMOBL_GPL then that's fine too.

Thanks,
Seth