[Qemu-devel] Re: [PATCH] QCOW2: fix bug - report read success on failure

[Kevin Wolf]

Am 03.02.2011 17:53, schrieb Chunqiang Tang:
> This patch fixes bugs in QCOW2's error handling paths of read operations.
> When an I/O operation fails, the QCOW2 driver mistakenly reports it as success
> to the uper layer.
> 
> This bug was found by Fast Virtual Disk (FVD)'s fully automated testing tool,
> when it injected failures. Specifically, the following test triggered the bug.
> 
> /bin/rm -rf /var/ramdisk/truth.raw /var/ramdisk/test.qcow2 
> /var/ramdisk/zero-500M.raw
> dd if=/dev/zero of=/var/ramdisk/truth.raw count=0 bs=1 seek=1112250368
> dd if=/dev/zero of=/var/ramdisk/zero-500M.raw count=0 bs=1 seek=575525376
> ./qemu-img create -f qcow2 -ocluster_size=65536,backing_fmt=blksim -b 
> /var/ramdisk/zero-500M.raw /var/ramdisk/test.qcow2 1112250368
> ./qemu-io --auto --seed=184915369 --truth=/var/ramdisk/truth.raw 
> --format=qcow2 --test=blksim:/var/ramdisk/test.qcow2 --verify_write=true 
> --compare_before=false --compare_after=true --round=100000 --parallel=100 
> --io_size=1048576 --fail_prob=0.1 --cancel_prob=0 --instant_qemubh=true
> 
> Signed-off-by: Chunqiang Tang <address@hidden>
> ---
>  block/qcow2.c |    8 ++++++--
>  1 files changed, 6 insertions(+), 2 deletions(-)
> 
> diff --git a/block/qcow2.c b/block/qcow2.c
> index 8c906d1..6f6d56f 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -479,8 +479,10 @@ static void qcow2_aio_read_cb(void *opaque, int ret)
>                  BLKDBG_EVENT(bs->file, BLKDBG_READ_BACKING_AIO);
>                  acb->hd_aiocb = bdrv_aio_readv(bs->backing_hd, 
> acb->sector_num,
>                                      &acb->hd_qiov, n1, qcow2_aio_read_cb, 
> acb);
> -                if (acb->hd_aiocb == NULL)
> +                if (acb->hd_aiocb == NULL) {
> +                    ret = -EIO;
>                      goto done;
> +                }
>              } else {
>                  ret = qcow2_schedule_bh(qcow2_aio_read_bh, acb);
>                  if (ret < 0)

Oops, thanks for catching this. I thought this was fixed long ago, but
apparently it wasn't.

> @@ -495,8 +497,10 @@ static void qcow2_aio_read_cb(void *opaque, int ret)
>          }
>      } else if (acb->cluster_offset & QCOW_OFLAG_COMPRESSED) {
>          /* add AIO support for compressed blocks ? */
> -        if (qcow2_decompress_cluster(bs, acb->cluster_offset) < 0)
> +        if (qcow2_decompress_cluster(bs, acb->cluster_offset) < 0) {
> +            ret = -EIO;
>              goto done;
> +        }

I think here we should change qcow2_decompessed_cluster() to return the
real error code instead of -1, so that we can pass it on instead of
turning everything into -EIO.

Kevin