linux-kernel - Re: [PATCH] init/do_mounts.c: treat EROFS like EACCES

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Date:	Mon, 23 Jun 2014 11:22:56 +0200
From:	Karel Zak <kzak@...hat.com>
To:	Philippe De Muyter <phdm@...qel.be>
Cc:	Dave Chinner <david@...morbit.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] init/do_mounts.c: treat EROFS like EACCES

On Fri, Jun 20, 2014 at 03:13:28PM +0200, Philippe De Muyter wrote:
> On Fri, Jun 20, 2014 at 09:09:24AM +1000, Dave Chinner wrote:
> > On Thu, Jun 19, 2014 at 02:19:50PM -0700, Andrew Morton wrote:
> > > On Wed, 18 Jun 2014 18:12:44 +0200 Philippe De Muyter <phdm@...qel.be> wrote:
> > > 
> > > > some combinations of filesystem and block device (at least vfat on mmc)
> > > > yield -EROFS instead of -EACCES when the device is read-only.  Retry
> > > > mounting with MS_RDONLY set, just like for the EACCES case, instead of
> > > > failing directly.
> > > > 
> > > > ...
> > > >
> > > > --- a/init/do_mounts.c
> > > > +++ b/init/do_mounts.c
> > > > @@ -394,6 +394,7 @@ retry:
> > > >  			case 0:
> > > >  				goto out;
> > > >  			case -EACCES:
> > > > +			case -EROFS:
> > > >  				flags |= MS_RDONLY;
> > > >  				goto retry;
> > > >  			case -EINVAL:
> > > 
> > > hm, what's going on here.  I'd have thought it to be very logical that
> > > file_system_type.mount() would return EROFS if the device is read-only!
> > > But I'm suspecting that there is some convention that the fs is
> > > supposed to return EACCES in this case.  So *perhaps* it is vfat-on-mmc
> > > which needs fixing.  Dunno.
> > > 
> > > Al, are you able to shed light?
> > 
> > from the mount(2) man page:
> > 
> > EACCES	A  component  of  a  path  was not searchable.  (See also
> > 	path_resolution(7).)  Or, mounting a read-only filesystem
> > 	was attempted without giving the MS_RDONLY flag.  Or, the
> > 	block device source is located on a filesystem mounted with
> > 	the MS_NODEV option.
> > 
> > So, when the device is read-only, the error should EACCES, not
> > EROFS. Would seem to me that vfat-on-mmc needs fixing...

Only code matters, we don't compile and execute man pages... ;-)

> Looking at the sources of mount(1)
> 
> https://github.com/karelzak/util-linux/blob/master/sys-utils/mount.c
> 
> at line 601, we clearly see that mount(1) allows mount(2) to fail
> with EROFS.

BTW, comment from the original mount(8) code:

     case EACCES:  /* pre-linux 1.1.38, 1.1.41 and later */
     case EROFS:   /* linux 1.1.38 and later */

 Karel

-- 
 Karel Zak  <kzak@...hat.com>
 http://karelzak.blogspot.com
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