On Mon, Mar 15 2010 at 11:10am -0400,
Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
>
>
> On Mon, 15 Mar 2010, Mike Snitzer wrote:
>
> > On Mon, Mar 15 2010 at 2:04am -0400,
> > Mikulas Patocka <mpatocka@xxxxxxxxxx> wrote:
> >
> > > Test chunk size against both origin and snapshot sector size
> > >
> > > Don't allow chunk size smaller than either origin or snapshot logical
> > > sector size. Reading or writing data unaligned to sector size is not allowed
> > > and causes immediate errors.
> > >
> > > Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>
> > >
> > > ---
> > > drivers/md/dm-exception-store.c | 4 +++-
> > > 1 file changed, 3 insertions(+), 1 deletion(-)
> > >
> > > Index: linux-2.6.34-rc1-devel/drivers/md/dm-exception-store.c
> > > ===================================================================
> > > --- linux-2.6.34-rc1-devel.orig/drivers/md/dm-exception-store.c 2010-03-12 14:38:31.000000000 +0100
> > > +++ linux-2.6.34-rc1-devel/drivers/md/dm-exception-store.c 2010-03-12 14:39:56.000000000 +0100
> > > @@ -173,7 +173,9 @@ int dm_exception_store_set_chunk_size(st
> > >
> > > /* Validate the chunk size against the device block size */
> > > if (chunk_size %
> > > - (bdev_logical_block_size(dm_snap_cow(store->snap)->bdev) >> 9)) {
> > > + (bdev_logical_block_size(dm_snap_cow(store->snap)->bdev) >> 9) ||
> > > + chunk_size %
> > > + (bdev_logical_block_size(dm_snap_origin(store->snap)->bdev) >> 9)) {
> > > *error = "Chunk size is not a multiple of device blocksize";
> > > return -EINVAL;
> > > }
> >
> > Shouldn't we split these checks out so that we can have more precise
> > error reporting? Ideally we'd share that chunk_size was not a multiple
> > of the "origin" or "snapshot" device's blocksize.
>
> You can split it to three messages ("not multiple of origin ... snapshot
> ... both devices' blocksize"), but I think it's not so important to be
> worth code size increase.
>
> > I was also thinking that we should avoid using %, e.g.:
> > (chunk_size & (bdev_logical_block_size(...) - 1))
> >
> > but AFAIK bdev_logical_block_size() may not be a power of 2 (MD allows
> > for obscure non-power of 2 blocksizes doesn't it? Or is that just for
> > MD chunk and stripe size?).
> >
> > Mike
>
> The Linux bio stack and page cache require that bdev_logical_block_size()
> is power of two.
OK, I'll have a look, but it sounds like we could use:
(chunk_size & (bdev_logical_block_size(...) - 1))
> But the disks can be reformatted to other block sizes.
> I'm wondering, what happens then ... I suppose it wouldn't even allow to
> use the disk. I will try.
Do you mean something like 512b logical and 4K physical? Such devices
must perform the appropriate r-m-w. A 4K formatted device will report
4K for both logical and physical (unless the device and format tool
allows for physical != logical).
Mike
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://www.redhat.com/mailman/listinfo/dm-devel
