Re: [Qemu-devel] [PATCH 01/11] block: switch blk_write_compressed() to byte-based interface

[Pavel Butsykin]

On 28.06.2016 13:53, Kevin Wolf wrote:
> Am 13.06.2016 um 16:23 hat Eric Blake geschrieben:
> > On 05/31/2016 03:15 AM, Denis V. Lunev wrote:
> > > From: Pavel Butsykin <address@hidden>
> > >
> > > This is a preparatory patch, which continues the general trend of the transition
> > > to the byte-based interfaces.
> > >
> > > Signed-off-by: Pavel Butsykin <address@hidden>
> > > Signed-off-by: Denis V. Lunev <address@hidden>
> > > CC: Jeff Cody <address@hidden>
> > > CC: Markus Armbruster <address@hidden>
> > > CC: Eric Blake <address@hidden>
> > > CC: John Snow <address@hidden>
> > > CC: Stefan Hajnoczi <address@hidden>
> > > CC: Kevin Wolf <address@hidden>
>
> > > -int bdrv_write_compressed(BlockDriverState *bs, int64_t sector_num,
> > > -                          const uint8_t *buf, int nb_sectors)
> > > +int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
> > > +                           const void *buf, int count)
> > >   {
> > >       BlockDriver *drv = bs->drv;
> > >       int ret;
> > > @@ -1791,14 +1791,15 @@ int bdrv_write_compressed(BlockDriverState *bs, int64_t 
> > > sector_num,
> > >       if (!drv->bdrv_write_compressed) {
> > >           return -ENOTSUP;
> > >       }
> > > -    ret = bdrv_check_request(bs, sector_num, nb_sectors);
> > > +    ret = bdrv_check_byte_request(bs, offset, count);
> > >       if (ret < 0) {
> > >           return ret;
> > >       }
> > >
> > >       assert(QLIST_EMPTY(&bs->dirty_bitmaps));
> > >
> > > -    return drv->bdrv_write_compressed(bs, sector_num, buf, nb_sectors);
> > > +    return drv->bdrv_write_compressed(bs, offset >> BDRV_SECTOR_BITS, buf,
> > > +                                      count >> BDRV_SECTOR_BITS);
> >
> > If you are going to shift right, you need to first assert that offset
> > and count are aligned (and thus that our call to a sector interface
> > isn't going to operate on the wrong data).  See for example commit 166fe960.
>
> Yes, I would like to have these assertions at least.
>
> But I'm wondering what the point of converting the interface is when we
> don't intend to actually support sub-sector requests and the sector
> alignment is still required at the end of the series.

Because at the time of sending patches, the format drivers still had
the sector-based interfaces. In the end, the assertions are not
necessary, because the interface format driver now also byte-based.

> Kevin