Re: [Qemu-devel] [PATCH v10 08/16] block: Support streaming to an intermediate layer

[Kevin Wolf <kwolf@redhat.com>]

Am 06.10.2016 um 15:02 hat Alberto Garcia geschrieben:
> This makes sure that the image we are streaming into is open in
> read-write mode during the operation.
> 
> Operation blockers are also set in all intermediate nodes, since they
> will be removed from the chain afterwards.
> 
> Finally, this also unblocks the stream operation in backing files.
> 
> Signed-off-by: Alberto Garcia <berto@igalia.com>
> ---
>  block.c        |  4 +++-
>  block/stream.c | 24 ++++++++++++++++++++++++
>  2 files changed, 27 insertions(+), 1 deletion(-)
> 
> diff --git a/block.c b/block.c
> index c80b528..8255d75 100644
> --- a/block.c
> +++ b/block.c
> @@ -1428,9 +1428,11 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd)
>              backing_hd->drv ? backing_hd->drv->format_name : "");
>  
>      bdrv_op_block_all(backing_hd, bs->backing_blocker);
> -    /* Otherwise we won't be able to commit due to check in bdrv_commit */
> +    /* Otherwise we won't be able to commit or stream */
>      bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_COMMIT_TARGET,
>                      bs->backing_blocker);
> +    bdrv_op_unblock(backing_hd, BLOCK_OP_TYPE_STREAM,
> +                    bs->backing_blocker);
>      /*
>       * We do backup in 3 ways:
>       * 1. drive backup
> diff --git a/block/stream.c b/block/stream.c
> index 3187481..b8ab89a 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -37,6 +37,7 @@ typedef struct StreamBlockJob {
>      BlockDriverState *base;
>      BlockdevOnError on_error;
>      char *backing_file_str;
> +    int bs_flags;
>  } StreamBlockJob;
>  
>  static int coroutine_fn stream_populate(BlockBackend *blk,
> @@ -81,6 +82,11 @@ static void stream_complete(BlockJob *job, void *opaque)
>          bdrv_set_backing_hd(bs, base);
>      }
>  
> +    /* Reopen the image back in read-only mode if necessary */
> +    if (s->bs_flags != bdrv_get_flags(bs)) {
> +        bdrv_reopen(bs, s->bs_flags, NULL);
> +    }
> +
>      g_free(s->backing_file_str);
>      block_job_completed(&s->common, data->ret);
>      g_free(data);
> @@ -220,6 +226,8 @@ void stream_start(const char *job_id, BlockDriverState *bs,
>                    BlockCompletionFunc *cb, void *opaque, Error **errp)
>  {
>      StreamBlockJob *s;
> +    BlockDriverState *iter;
> +    int orig_bs_flags;
>  
>      s = block_job_create(job_id, &stream_job_driver, bs, speed,
>                           cb, opaque, errp);
> @@ -227,8 +235,24 @@ void stream_start(const char *job_id, BlockDriverState *bs,
>          return;
>      }
>  
> +    /* Make sure that the image is opened in read-write mode */
> +    orig_bs_flags = bdrv_get_flags(bs);
> +    if (!(orig_bs_flags & BDRV_O_RDWR)) {
> +        if (bdrv_reopen(bs, orig_bs_flags | BDRV_O_RDWR, errp) != 0) {
> +            block_job_unref(&s->common);
> +            return;
> +        }
> +    }
> +
> +    /* Block all intermediate nodes between bs and base, because they
> +     * will disappear from the chain after this operation */
> +    for (iter = backing_bs(bs); iter && iter != base; iter = backing_bs(iter)) {
> +        block_job_add_bdrv(&s->common, iter);
> +    }

In patch 6, you had a comment that the top node must be blocked as well
because its backing file string will be updated. Isn't it the same for
streaming?

>      s->base = base;
>      s->backing_file_str = g_strdup(backing_file_str);
> +    s->bs_flags = orig_bs_flags;
>  
>      s->on_error = on_error;
>      s->common.co = qemu_coroutine_create(stream_run, s);

Kevin