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

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Message-ID: <20140619230924.GO4453@dastard>
Date:	Fri, 20 Jun 2014 09:09:24 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Philippe De Muyter <phdm@...qel.be>, linux-kernel@...r.kernel.org,
	Al Viro <viro@...iv.linux.org.uk>
Subject: Re: [PATCH] init/do_mounts.c: treat EROFS like EACCES

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...

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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