[2/3] virtio-blk: Bypass error action and I/O accounting on invalid r/w

When a device model's I/O operation fails, we execute the error
action.  This lets layers above QEMU implement thin provisioning, or
attempt to correct errors before they reach the guest.  But when the
I/O operation fails because its invalid, reporting the error to the
guest is the only sensible action.

If the guest's read or write asks for an invalid sector range, fail
the request right away, without considering the error action.  No
change with error action BDRV_ACTION_REPORT.

Furthermore, bypass I/O accounting, because we want to track only I/O
that actually reaches the block layer.

The next commit will extend "invalid sector range" to cover attempts
to read/write beyond the end of the medium.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 hw/block/virtio-blk.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

On Thu, 06/05 14:15, Markus Armbruster wrote:
> When a device model's I/O operation fails, we execute the error
> action.  This lets layers above QEMU implement thin provisioning, or
> attempt to correct errors before they reach the guest.  But when the
> I/O operation fails because its invalid, reporting the error to the

s/its/it's/ ?

Anyway,

Reviewed-by: Fam Zheng <famz@redhat.com>

> guest is the only sensible action.
> 
> If the guest's read or write asks for an invalid sector range, fail
> the request right away, without considering the error action.  No
> change with error action BDRV_ACTION_REPORT.
> 
> Furthermore, bypass I/O accounting, because we want to track only I/O
> that actually reaches the block layer.
> 
> The next commit will extend "invalid sector range" to cover attempts
> to read/write beyond the end of the medium.
> 
> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> ---
>  hw/block/virtio-blk.c | 14 ++++++++------
>  1 file changed, 8 insertions(+), 6 deletions(-)
> 
> diff --git a/hw/block/virtio-blk.c b/hw/block/virtio-blk.c
> index f2b4dca..2c68d0d 100644
> --- a/hw/block/virtio-blk.c
> +++ b/hw/block/virtio-blk.c
> @@ -300,15 +300,16 @@ static void virtio_blk_handle_write(VirtIOBlockReq *req, MultiReqBuffer *mrb)
>  
>      sector = ldq_p(&req->out->sector);
>  
> -    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_WRITE);
> -
>      trace_virtio_blk_handle_write(req, sector, req->qiov.size / 512);
>  
>      if (!virtio_blk_sect_range_ok(req->dev, sector, req->qiov.size)) {
> -        virtio_blk_rw_complete(req, -EIO);
> +        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
> +        g_free(req);
>          return;
>      }
>  
> +    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_WRITE);
> +
>      if (mrb->num_writes == 32) {
>          virtio_submit_multiwrite(req->dev->bs, mrb);
>      }
> @@ -330,14 +331,15 @@ static void virtio_blk_handle_read(VirtIOBlockReq *req)
>  
>      sector = ldq_p(&req->out->sector);
>  
> -    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_READ);
> -
>      trace_virtio_blk_handle_read(req, sector, req->qiov.size / 512);
>  
>      if (!virtio_blk_sect_range_ok(req->dev, sector, req->qiov.size)) {
> -        virtio_blk_rw_complete(req, -EIO);
> +        virtio_blk_req_complete(req, VIRTIO_BLK_S_IOERR);
> +        g_free(req);
>          return;
>      }
> +
> +    bdrv_acct_start(req->dev->bs, &req->acct, req->qiov.size, BDRV_ACCT_READ);
>      bdrv_aio_readv(req->dev->bs, sector, &req->qiov,
>                     req->qiov.size / BDRV_SECTOR_SIZE,
>                     virtio_blk_rw_complete, req);
> -- 
> 1.9.3
> 
>

On 06/05/2014 09:18 PM, Fam Zheng wrote:
> On Thu, 06/05 14:15, Markus Armbruster wrote:
>> When a device model's I/O operation fails, we execute the error
>> action.  This lets layers above QEMU implement thin provisioning, or
>> attempt to correct errors before they reach the guest.  But when the
>> I/O operation fails because its invalid, reporting the error to the
> 
> s/its/it's/ ?

Yes, this is a case where you are contracting "it is" into "it's"

Fam Zheng <famz@redhat.com> writes:

> On Thu, 06/05 14:15, Markus Armbruster wrote:
>> When a device model's I/O operation fails, we execute the error
>> action.  This lets layers above QEMU implement thin provisioning, or
>> attempt to correct errors before they reach the guest.  But when the
>> I/O operation fails because its invalid, reporting the error to the
>
> s/its/it's/ ?

Of course.  Perhaps it can be fixed on commit.

> Anyway,
>
> Reviewed-by: Fam Zheng <famz@redhat.com>

Thanks!