Re: [PATCH 1/2] Btrfs: add more valid checks for superblock

[Liu Bo <bo.li.liu@oracle.com>]

On Wed, May 04, 2016 at 03:23:29PM +0200, David Sterba wrote:
> On Tue, May 03, 2016 at 09:02:56AM +0800, Qu Wenruo wrote:
> > 
> > 
> > Liu Bo wrote on 2016/05/02 11:15 -0700:
> > > This adds valid checks for super_total_bytes, super_bytes_used and
> > > super_stripesize.
> > >
> > > Reported-by: Vegard Nossum <vegard.nossum@oracle.com>
> > > Reported-by: Quentin Casasnovas <quentin.casasnovas@oracle.com>
> > > Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
> > > ---
> > >  fs/btrfs/disk-io.c | 14 ++++++++++++++
> > >  1 file changed, 14 insertions(+)
> > >
> > > diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
> > > index 4e47849..988d03f 100644
> > > --- a/fs/btrfs/disk-io.c
> > > +++ b/fs/btrfs/disk-io.c
> > > @@ -4120,6 +4120,20 @@ static int btrfs_check_super_valid(struct btrfs_fs_info *fs_info,
> > >  	 * Hint to catch really bogus numbers, bitflips or so, more exact checks are
> > >  	 * done later
> > >  	 */
> > > +	if (btrfs_super_total_bytes(sb) == 0) {
> > > +		printk(KERN_ERR "BTRFS: total bytes is zero\n");
> > > +		ret = -EINVAL;
> > > +	}
> > 
> > Would it be better if using "6 * nodesize"?
> > 
> > I'd like to use a precious low limit on total bytes, but we don't have 
> > such value, so 6 nodesize would be good.
> 
> An early check can compare against some reasonable value, but the
> total_bytes value must be equal to the sum of all device sizes
> (disk_total_bytes). I'm not sure if we have enough information to verify
> that at this point though.

That's what I had in mind, the problem is that only the first device information is recorded in superblock.

At this moment We have device_num but we don't know the size of other devices.

Thanks,

-liubo