[dm-devel] dm raid: pointer math issue in super_sync()
Mike Snitzer
snitzer at redhat.com
Tue Oct 21 13:25:19 UTC 2014
On Tue, Oct 21 2014 at 8:57am -0400,
Dan Carpenter <dan.carpenter at oracle.com> wrote:
> On Tue, Oct 21, 2014 at 08:48:26AM -0400, Mike Snitzer wrote:
> > > - memset(sb + sizeof(*sb), 0, rdev->sb_size - sizeof(*sb));
> > > + memset(sb + 1, 0, rdev->sb_size - sizeof(*sb));
> > >
> > > sb->magic = cpu_to_le32(DM_RAID_MAGIC);
> > > sb->features = cpu_to_le32(0); /* No features yet */
> >
> > Not following... sizeof(*sb) != sizeof(sb). So I'm not seeing a
> > problem.
> >
> > Nor am I seeing how you think sb + 1 is equivalent to what Heinz
> > intended (zero the memory following the sizeof(struct dm_raid_superblock)).
>
> It's pointer math.
Yes, I see that now..
> sizeof(*sb) is 512.
>
> "sb + sizeof(*sb)" is the same as (void *)sb + 512 * 512.
> "sb + 1" is the same as (void *)sb + 512.
Actually, Heinz removed the 452 bytes of padding from struct
dm_raid_superblock, so it is more like:
sizeof(*sb) == sizeof(struct dm_raid_super_block) == 60
"sb + sizeof(*sb)" is the same as (void *)sb + 60 * 60
"sb + 1" is the same as (void *)sb + 60.
But regardless, your broader point on the math stands. I'll get this
fixed up, thanks!
Mike
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