Re: [Qemu-devel] [Qemu-block] [PATCH v2 4/8] qcow: Switch qcow_co_writev to byte-based calls

[Jeff Cody <jcody@redhat.com>]

On Thu, May 31, 2018 at 03:50:42PM -0500, Eric Blake wrote:
> We are gradually moving away from sector-based interfaces, towards
> byte-based.  Make the change for the internals of the qcow
> driver write function, by iterating over offset/bytes instead of
> sector_num/nb_sectors, and with a rename of index_in_cluster and
> repurposing of n to track bytes instead of sectors.
> 
> A later patch will then switch the qcow driver as a whole over
> to byte-based operation.
> 
> Signed-off-by: Eric Blake <eblake@redhat.com>
> 
> ---
> v2: prefer 64-bit * over 23-bit <<, rename variable for legibility [Kevin]
> ---
>  block/qcow.c | 36 +++++++++++++++++-------------------
>  1 file changed, 17 insertions(+), 19 deletions(-)
> 
> diff --git a/block/qcow.c b/block/qcow.c
> index b90915218ff..44adeba276c 100644
> --- a/block/qcow.c
> +++ b/block/qcow.c
> @@ -723,13 +723,15 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
>                                         int flags)
>  {
>      BDRVQcowState *s = bs->opaque;
> -    int index_in_cluster;
> +    int offset_in_cluster;
>      uint64_t cluster_offset;
>      int ret = 0, n;
>      struct iovec hd_iov;
>      QEMUIOVector hd_qiov;
>      uint8_t *buf;
>      void *orig_buf;
> +    int64_t offset = sector_num * BDRV_SECTOR_SIZE;
> +    int64_t bytes = nb_sectors * BDRV_SECTOR_SIZE;
> 
>      assert(!flags);
>      s->cluster_cache_offset = -1; /* disable compressed cache */
> @@ -749,16 +751,14 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
> 
>      qemu_co_mutex_lock(&s->lock);
> 
> -    while (nb_sectors != 0) {
> -
> -        index_in_cluster = sector_num & (s->cluster_sectors - 1);
> -        n = s->cluster_sectors - index_in_cluster;
> -        if (n > nb_sectors) {
> -            n = nb_sectors;
> +    while (bytes != 0) {
> +        offset_in_cluster = offset & (s->cluster_size - 1);
> +        n = s->cluster_size - offset_in_cluster;
> +        if (n > bytes) {
> +            n = bytes;
>          }
> -        ret = get_cluster_offset(bs, sector_num << 9, 1, 0,
> -                                 index_in_cluster << 9,
> -                                 (index_in_cluster + n) << 9, &cluster_offset);
> +        ret = get_cluster_offset(bs, offset, 1, 0, offset_in_cluster,
> +                                 offset_in_cluster + n, &cluster_offset);
>          if (ret < 0) {
>              break;
>          }
> @@ -768,30 +768,28 @@ static coroutine_fn int qcow_co_writev(BlockDriverState *bs, int64_t sector_num,
>          }
>          if (bs->encrypted) {
>              assert(s->crypto);
> -            if (qcrypto_block_encrypt(s->crypto, sector_num * BDRV_SECTOR_SIZE,
> -                                      buf, n * BDRV_SECTOR_SIZE, NULL) < 0) {
> +            if (qcrypto_block_encrypt(s->crypto, offset, buf, n, NULL) < 0) {
>                  ret = -EIO;
>                  break;
>              }
>          }
> 
>          hd_iov.iov_base = (void *)buf;
> -        hd_iov.iov_len = n * 512;
> +        hd_iov.iov_len = n;
>          qemu_iovec_init_external(&hd_qiov, &hd_iov, 1);
>          qemu_co_mutex_unlock(&s->lock);
>          BLKDBG_EVENT(bs->file, BLKDBG_WRITE_AIO);
> -        ret = bdrv_co_writev(bs->file,
> -                             (cluster_offset >> 9) + index_in_cluster,
> -                             n, &hd_qiov);
> +        ret = bdrv_co_pwritev(bs->file, cluster_offset + offset_in_cluster,
> +                              n, &hd_qiov, 0);
>          qemu_co_mutex_lock(&s->lock);
>          if (ret < 0) {
>              break;
>          }
>          ret = 0;
> 
> -        nb_sectors -= n;
> -        sector_num += n;
> -        buf += n * 512;
> +        bytes -= n;
> +        offset += n;
> +        buf += n;
>      }
>      qemu_co_mutex_unlock(&s->lock);
> 
> -- 
> 2.14.3
> 
> 

Reviewed-by: Jeff Cody <jcody@redhat.com>