[Qemu-devel] [PATCH 09/30] block/curl: Handle failed reads gracefully.

[Kevin Wolf <kwolf@redhat.com>]

From: Nicholas Thomas <nick@bytemark.co.uk>

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>
---
 block/curl.c |   20 +++++++++++++++++++-
 1 files changed, 19 insertions(+), 1 deletions(-)

diff --git a/block/curl.c b/block/curl.c
index 5c157bc..f3f61cc 100644
--- a/block/curl.c
+++ b/block/curl.c
@@ -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
-- 
1.7.6