[Qemu-devel] [PATCH v2 2/5] nbd/server: fix sparse read

[Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>]

In case of io error in nbd_co_send_sparse_read we should not
"goto reply:", as it is fatal error and common behavior is
disconnect in this case. We should not try to send client an
error reply, representing channel-io error on previous try to
send a reply.

Fix this by handle block-status error in nbd_co_send_sparse_read,
so nbd_co_send_sparse_read fails only on io error. Then just skip
common "reply:" code path in nbd_trip.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
---

v2: code movement splitted to 01
    remove error_report
    fix indent
    fix commit message subject line
    add comment to nbd_co_send_sparse_read (be free to adjust it)

 nbd/server.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/nbd/server.c b/nbd/server.c
index c406b0656d..e0de431e10 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1365,6 +1365,10 @@ static int coroutine_fn nbd_co_send_structured_error(NBDClient *client,
     return nbd_co_send_iov(client, iov, 1 + !!iov[1].iov_len, errp);
 }
 
+/* Do sparse read and send structured reply to the client.
+ * Returns -errno if sending fails. bdrv_block_status_above() fail is not
+ * considered as an error, but reported to the client instead (as a structured
+ * error). */
 static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
                                                 uint64_t handle,
                                                 uint64_t offset,
@@ -1385,8 +1389,13 @@ static int coroutine_fn nbd_co_send_sparse_read(NBDClient *client,
         bool final;
 
         if (status < 0) {
-            error_setg_errno(errp, -status, "unable to check for holes");
-            return status;
+            char *msg = g_strdup_printf("unable to check for holes: %s",
+                                        strerror(-status));
+
+            ret = nbd_co_send_structured_error(client, handle, -status, msg,
+                                               errp);
+            g_free(msg);
+            return ret;
         }
         assert(pnum && pnum <= size - progress);
         final = progress + pnum == size;
@@ -1567,7 +1576,7 @@ static coroutine_fn void nbd_trip(void *opaque)
                                           request.from, req->data, request.len,
                                           &local_err);
             if (ret < 0) {
-                goto reply;
+                goto replied;
             }
             goto done;
         }
@@ -1664,6 +1673,8 @@ reply:
                                        req->data, reply_data_len, &local_err);
     }
     g_free(msg);
+
+replied:
     if (ret < 0) {
         error_prepend(&local_err, "Failed to send reply: ");
         goto disconnect;
-- 
2.11.1