"Richard W.M. Jones" <rjo...@redhat.com> writes: > 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 <rjo...@redhat.com> > Reviewed-by: Stefan Hajnoczi <stefa...@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]; >
Printing an error message, then returning an error code is problematic. It works when the caller is going to print its own error message to the same destination. Callee produces a specific error message devoid of context, caller produces an unspecific one with hopefully more context. Better than just one of them. Worse than a single specific error with context, but that can't be done with just a "return errno code" interface. It's kind of wrong when the caller reports its own error somewhere else, e.g. to a monitor. Still, when barfing extra info to stderr is the best we can do, it's better than nothing. It's more wrong when the caller handles the error quietly. I guess that's never the case here, but I can't be sure without a lot more sleuthing. Perhaps Kevin or Stefan can judge this immediately. > @@ -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; > } To understand impact exactly, we'd need to figure out where the changed error code gets consumed. However, I don't expect consumers to check the actual error code. A quick grep for comparisons with EIO or -EIO finds nothing related to block I/O, except for nbd_trip() checking the value of nbd_co_receive_request(), and that's unrelated.