Re: [Qemu-devel] [PATCH] block/curl: Don't lose original error when a connection fails.

[John Snow <jsnow@redhat.com>]

On 06/25/2015 03:39 PM, Richard W.M. Jones wrote:
> Currently if qemu is connected to a curl source (eg. web server), and
> the web server fails / times out / dies, you always see a bogus EIO
> "Input/output error".
> 
> For example, choose a large file located on any local webserver which
> you control:
> 
>   $ qemu-img convert -p http://example.com/large.iso /tmp/test
> 
> Once it starts copying the file, stop the webserver and you will see
> qemu-img fail with:
> 
>   qemu-img: error while reading sector 61440: Input/output error
> 
> This patch does two things: Firstly print the actual error from curl
> so it doesn't get lost.  Secondly, change EIO to EPROTO.  EPROTO is a
> POSIX.1 compatible errno which more accurately reflects that there was
> a protocol error, rather than some kind of hardware failure.
> 
> After this patch is applied, the error changes to:
> 
>   $ qemu-img convert -p http://example.com/large.iso /tmp/test
>   qemu-img: curl: transfer closed with 469989 bytes remaining to read
>   qemu-img: error while reading sector 16384: Protocol error
> 
> Signed-off-by: Richard W.M. Jones <rjones@redhat.com>
> ---
>  block/curl.c | 9 ++++++++-
>  1 file changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/block/curl.c b/block/curl.c
> index 3a2b63e..2fd7c06 100644
> --- a/block/curl.c
> +++ b/block/curl.c
> @@ -22,6 +22,7 @@
>   * THE SOFTWARE.
>   */
>  #include "qemu-common.h"
> +#include "qemu/error-report.h"
>  #include "block/block_int.h"
>  #include "qapi/qmp/qbool.h"
>  #include "qapi/qmp/qstring.h"
> @@ -298,6 +299,12 @@ static void curl_multi_check_completion(BDRVCURLState *s)
>              /* ACBs for successful messages get completed in curl_read_cb */
>              if (msg->data.result != CURLE_OK) {
>                  int i;
> +
> +                /* Don't lose the original error message from curl, since
> +                 * it contains extra data.
> +                 */
> +                error_report("curl: %s", state->errmsg);
> +
>                  for (i = 0; i < CURL_NUM_ACB; i++) {
>                      CURLAIOCB *acb = state->acb[i];
>  
> @@ -305,7 +312,7 @@ static void curl_multi_check_completion(BDRVCURLState *s)
>                          continue;
>                      }
>  
> -                    acb->common.cb(acb->common.opaque, -EIO);
> +                    acb->common.cb(acb->common.opaque, -EPROTO);
>                      qemu_aio_unref(acb);
>                      state->acb[i] = NULL;
>                  }
> 

We'll see what Markus says! ;) I think it's a strict improvement.

Reviewed-by: John Snow <jsnow@redhat.com>