Re: [Qemu-devel] [PATCH 02/11] block/io: add bdrv_co_write_compressed

[Pavel Butsykin]

On 28.06.2016 14:09, Kevin Wolf wrote:
> Am 31.05.2016 um 11:15 hat Denis V. Lunev geschrieben:
> > From: Pavel Butsykin <address@hidden>
> >
> > This patch just adds the interface to the bdrv_co_pwritev_compressed,
> > which is currently not used but will be useful for safe implementation of the
> > bdrv_co_write_compressed callback in format drivers.
> >
> > 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>
> > ---
> >   block/io.c                | 78 +++++++++++++++++++++++++++++++++++++++++++----
> >   include/block/block_int.h |  5 +++
> >   qemu-img.c                |  2 +-
> >   3 files changed, 78 insertions(+), 7 deletions(-)
> >
> > diff --git a/block/io.c b/block/io.c
> > index c5bb6ae..54cd9a4 100644
> > --- a/block/io.c
> > +++ b/block/io.c
> > @@ -1779,8 +1779,8 @@ int bdrv_is_allocated_above(BlockDriverState *top,
> >       return 0;
> >   }
> >
> > -int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
> > -                           const void *buf, int count)
> > +int coroutine_fn bdrv_co_pwritev_compressed(BlockDriverState *bs,
> > +    int64_t offset, unsigned int bytes, QEMUIOVector *qiov)
> >   {
> >       BlockDriver *drv = bs->drv;
> >       int ret;
> > @@ -1788,18 +1788,84 @@ int bdrv_pwrite_compressed(BlockDriverState *bs, 
> > int64_t offset,
> >       if (!drv) {
> >           return -ENOMEDIUM;
> >       }
> > -    if (!drv->bdrv_write_compressed) {
> > +
> > +    if (!drv->bdrv_co_write_compressed) {
> >           return -ENOTSUP;
> >       }
> > -    ret = bdrv_check_byte_request(bs, offset, count);
> > +
> > +    ret = bdrv_check_byte_request(bs, offset, bytes);
> >       if (ret < 0) {
> >           return ret;
> >       }
> >
> >       assert(QLIST_EMPTY(&bs->dirty_bitmaps));
> > +    assert(qemu_in_coroutine());
> > +
> > +    return drv->bdrv_co_write_compressed(bs, offset >> BDRV_SECTOR_BITS,
> > +                                         bytes >> BDRV_SECTOR_BITS, qiov);
> > +}
> > +
> > +typedef struct BdrvWriteCompressedCo {
> > +    BlockDriverState *bs;
> > +    int64_t offset;
> > +    QEMUIOVector *qiov;
> > +    int ret;
> > +} BdrvWriteCompressedCo;
>
> I think you could just reuse RwCo here.

I reused BlkRwCo, and it's only a temporary change.

> And in fact, this made we wonder whether we can reuse more from the
> normal I/O path. If compressed writes could be made just another REQ_*
> flag and we went through bdrv_co_pwritev(), we would automatically get
> the alignment code if we don't want to convert drivers to byte-based.
> And also the existing coroutine wrapper code would be reused instead
> implementing it once more.
>
> I'm not completely sure how special compressed writes really are, so
> reusing the normal I/O path may or may not work. It might be worth
> investigating, though.
>
> > --- a/include/block/block_int.h
> > +++ b/include/block/block_int.h
> > @@ -207,6 +207,9 @@ struct BlockDriver {
> >       int (*bdrv_write_compressed)(BlockDriverState *bs, int64_t sector_num,
> >                                    const uint8_t *buf, int nb_sectors);
> >
> > +    int coroutine_fn (*bdrv_co_write_compressed)(BlockDriverState *bs,
> > +        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);
>
> This should be called bdrv_co_writev_compressed because it's a vectored
> interface.
agree

> Kevin