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block/curl: Handle failed reads gracefully. 

Current behaviour if a read fails is for the acb to not get finished.
This causes an infinite loop in bdrv_read_em (block.c). The read failure
never gets reported to the  guest and if the error condition clears, the
process never recovers.

With this patch, when curl reports a failure we finish the acb as a
failure. This results in the guest receiving an I/O error (rather than
the read hanging indefinitely) and if the error condition subsequently
clears, retries work as expected.

The simplest test is to put an ISO on a web server you have control over
and open it with qemu-io. Then move the ISO out of the way and attempt
to read some data - you should see behaviour matching the above.

Signed-off-by: Nick Thomas <nick@bytemark.co.uk>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Nicholas Thomas 2011-08-15 10:00:34 +01:00 committed by Kevin Wolf
parent 3fba9d8198
commit f785a5ae36
1 changed files with 19 additions and 1 deletions
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20
block/curl.c
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@ -229,6 +229,23 @@ static void curl_multi_do(void *arg)
{
CURLState *state = NULL;
curl_easy_getinfo(msg->easy_handle, CURLINFO_PRIVATE, (char**)&state);
/* ACBs for successful messages get completed in curl_read_cb */
if (msg->data.result != CURLE_OK) {
int i;
for (i = 0; i < CURL_NUM_ACB; i++) {
CURLAIOCB *acb = state->acb[i];
if (acb == NULL) {
continue;
}
acb->common.cb(acb->common.opaque, -EIO);
qemu_aio_release(acb);
state->acb[i] = NULL;
}
}
curl_clean_state(state);
break;
}
@ -277,7 +294,8 @@ static CURLState *curl_init_state(BDRVCURLState *s)
curl_easy_setopt(state->curl, CURLOPT_FOLLOWLOCATION, 1);
curl_easy_setopt(state->curl, CURLOPT_NOSIGNAL, 1);
curl_easy_setopt(state->curl, CURLOPT_ERRORBUFFER, state->errmsg);
curl_easy_setopt(state->curl, CURLOPT_FAILONERROR, 1);
#ifdef DEBUG_VERBOSE
curl_easy_setopt(state->curl, CURLOPT_VERBOSE, 1);
#endif