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

[Eric Blake <eblake@redhat.com>]

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On 05/31/2016 03:15 AM, Denis V. Lunev wrote:
> From: Pavel Butsykin <pbutsykin@virtuozzo.com>
> 
> 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 <pbutsykin@virtuozzo.com>
> Signed-off-by: Denis V. Lunev <den@openvz.org>
> CC: Jeff Cody <jcody@redhat.com>
> CC: Markus Armbruster <armbru@redhat.com>
> CC: Eric Blake <eblake@redhat.com>
> CC: John Snow <jsnow@redhat.com>
> CC: Stefan Hajnoczi <stefanha@redhat.com>
> CC: Kevin Wolf <kwolf@redhat.com>
> ---
>  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)

Why the rename s/count/bytes/?  Would it be better to get the name right
in 1/11?

>  {
>      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;

This is a (temporary) regression - since none of the drivers have
.bdrv_co_write_compressed yet, you will always fail.  Rather, the
transition period should support both interfaces at once...

>      }
> -    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);

...and call into either the old or the new interface according to what
is present.


> +int bdrv_pwrite_compressed(BlockDriverState *bs, int64_t offset,
> +                           const void *buf, int count)
> +{
> +    BdrvWriteCompressedCo data;
> +    QEMUIOVector qiov;
> +    BlockDriver *drv = bs->drv;
> +    struct iovec iov = {
> +        .iov_base = (void *)buf,
> +        .iov_len = count,
> +    };
> +    qemu_iovec_init_external(&qiov, &iov, 1);
>  
> -    return drv->bdrv_write_compressed(bs, offset >> BDRV_SECTOR_BITS, buf,
> -                                      count >> BDRV_SECTOR_BITS);
> +    data = (BdrvWriteCompressedCo) {
> +        .bs     = bs,
> +        .offset = offset,
> +        .qiov   = &qiov,
> +        .ret    = -EINPROGRESS,
> +    };
> +
> +    if (!drv) {
> +        return -ENOMEDIUM;
> +    }
> +
> +    if (drv->bdrv_write_compressed) {
> +        int 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, offset >> BDRV_SECTOR_BITS, buf,
> +                                          count >> BDRV_SECTOR_BITS);
> +    }

Oh, you're catering to the old code up front, without a coroutine, and
only the new code gets coroutine treatment.  Maybe it's okay after all.

> +
> +    if (qemu_in_coroutine()) {
> +        /* Fast-path if already in coroutine context */
> +        bdrv_write_compressed_co_entry(&data);
> +    } else {
> +        AioContext *aio_context = bdrv_get_aio_context(bs);
> +
> +        Coroutine *co = qemu_coroutine_create(bdrv_write_compressed_co_entry);
> +        qemu_coroutine_enter(co, &data);
> +        while (data.ret == -EINPROGRESS) {
> +            aio_poll(aio_context, true);
> +        }
> +    }
> +    return data.ret;
>  }
>  
>  int bdrv_save_vmstate(BlockDriverState *bs, const uint8_t *buf,
> diff --git a/include/block/block_int.h b/include/block/block_int.h
> index 30a9717..ccba9c9 100644
> --- 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,

Might be better to name this bdrv_co_pwrite_compressed if we want to
make it byte-based...

> +        int64_t sector_num, int nb_sectors, QEMUIOVector *qiov);

...it seems odd that you have to add a new sector-based interface given
that you are trying to convert to byte-based.

> +
>      int (*bdrv_snapshot_create)(BlockDriverState *bs,
>                                  QEMUSnapshotInfo *sn_info);
>      int (*bdrv_snapshot_goto)(BlockDriverState *bs,
> @@ -535,6 +538,8 @@ int coroutine_fn bdrv_co_preadv(BlockDriverState *bs,
>  int coroutine_fn bdrv_co_pwritev(BlockDriverState *bs,
>      int64_t offset, unsigned int bytes, QEMUIOVector *qiov,
>      BdrvRequestFlags flags);
> +int coroutine_fn bdrv_co_pwritev_compressed(BlockDriverState *bs,
> +    int64_t offset, unsigned int bytes, QEMUIOVector *qiov);
>  
>  int get_tmp_filename(char *filename, int size);
>  BlockDriver *bdrv_probe_all(const uint8_t *buf, int buf_size,
> diff --git a/qemu-img.c b/qemu-img.c
> index eb744d4..ab54027 100644
> --- a/qemu-img.c
> +++ b/qemu-img.c
> @@ -2024,7 +2024,7 @@ static int img_convert(int argc, char **argv)
>          const char *preallocation =
>              qemu_opt_get(opts, BLOCK_OPT_PREALLOC);
>  
> -        if (!drv->bdrv_write_compressed) {
> +        if (!drv->bdrv_write_compressed && !drv->bdrv_co_write_compressed) {
>              error_report("Compression not supported for this file format");
>              ret = -1;
>              goto out;
> 

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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