Re: [Qemu-devel] [PATCH v2 for-1.2 1/2] stream: complete early if end of backing file is reached

[Paolo Bonzini <pbonzini@redhat.com>]

Il 28/08/2012 16:26, Stefan Hajnoczi ha scritto:
> It is possible to create an image that is larger than its backing file.
> Reading beyond the end of the backing file produces zeroes if no writes
> have been made to those sectors in the image file.
> 
> This patch finishes streaming early when the end of the backing file is
> reached.  Without this patch the block job hangs and continually tries
> to stream the first sectors beyond the end of the backing file.
> 
> To reproduce the hung block job bug:
> 
>   $ qemu-img create -f qcow2 backing.qcow2 128M
>   $ qemu-img create -f qcow2 -o backing_file=backing.qcow2 image.qcow2 6G
>   $ qemu -drive if=virtio,cache=none,file=image.qcow2
>   (qemu) block_stream virtio0
>   (qemu) info block-jobs
> 
> The qemu-iotests 030 streaming test still passes.
> 
> Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
> ---
>  block/stream.c |    6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/block/stream.c b/block/stream.c
> index 37c4652..c4f87dd 100644
> --- a/block/stream.c
> +++ b/block/stream.c
> @@ -122,6 +122,12 @@ wait:
>               * known-unallocated area [sector_num, sector_num+n).  */
>              ret = bdrv_co_is_allocated_above(bs->backing_hd, base,
>                                               sector_num, n, &n);
> +
> +            /* Finish early if end of backing file has been reached */
> +            if (ret == 0 && n == 0) {
> +                n = end - sector_num;
> +            }

Reviewed-by: Paolo Bonzini <pbonzini@gnu.org>

>              copy = (ret == 1);
>          }
>          trace_stream_one_iteration(s, sector_num, n, ret);
>