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Date:   Mon, 21 Oct 2019 15:04:24 +0100
From:   Al Viro <viro@zeniv.linux.org.uk>
To:     David Howells <dhowells@redhat.com>
Cc:     Nicolas Pitre <nico@fluxnic.net>, Maxime Bizon <mbizon@freebox.fr>,
        linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH] cramfs: fix usage on non-MTD device
Message-ID: <20191021140424.GU26530@ZenIV.linux.org.uk>
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On Mon, Oct 21, 2019 at 02:45:39PM +0100, David Howells wrote:
> Nicolas Pitre <nico@fluxnic.net> wrote:
> 
> > From: Maxime Bizon <mbizon@freebox.fr>
> > 
> > When both CONFIG_CRAMFS_MTD and CONFIG_CRAMFS_BLOCKDEV are enabled, if
> > we fail to mount on MTD, we don't try on block device.
> > 
> > Fixes: 74f78fc5ef43 ("vfs: Convert cramfs to use the new mount API")
> > 
> > Signed-off-by: Maxime Bizon <mbizon@freebox.fr>
> > Signed-off-by: Nicolas Pitre <nico@fluxnic.net>
> 
> Acked-by: David Howells <dhowells@redhat.com>

FWIW, the thing that worries me here is the possibility of
side effects on fs_context in case if fill_super fails really
late...  OTOH, cramfs one seems to be safe in that respect.

OK, will apply, but that's fairly brittle and needs to be
documented.  If we *ever* grow non-trivial options parsing
there, that'll be a serious landmine.  If something gets
transferred from fs_context into a superblock, which
fails later in setup and takes that object with it, the
second part (get_tree_bdev()) would be in trouble.