[Qemu-devel] [PATCH] Avoid permanently disabled QEMU monitor when UNIX migration fails

[Qemu-devel] [PATCH] Avoid permanently disabled QEMU monitor when UNIX migration fails

[Daniel P. Berrange]

If a UNIX migration command is attempt to a UNIX socket which does
not exist, then the monitor is suspended, but never resumed. This
prevents any further use of the monitor

* migration-unix.c: Only call migrate_fd_monitor_suspend() once
  connected to the UNIX socket.
---
 migration-unix.c |   12 +++++++-----
 1 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/migration-unix.c b/migration-unix.c
index 783228b..a141dbb 100644
--- a/migration-unix.c
+++ b/migration-unix.c
@@ -112,10 +112,6 @@ MigrationState *unix_start_outgoing_migration(Monitor *mon,
 
     socket_set_nonblock(s->fd);
 
-    if (!detach) {
-        migrate_fd_monitor_suspend(s, mon);
-    }
-
     do {
         ret = connect(s->fd, (struct sockaddr *)&addr, sizeof(addr));
         if (ret == -1)
@@ -128,7 +124,13 @@ MigrationState *unix_start_outgoing_migration(Monitor *mon,
     if (ret < 0 && ret != -EINPROGRESS && ret != -EWOULDBLOCK) {
         dprintf("connect failed\n");
         goto err_after_open;
-    } else if (ret >= 0)
+    }
+
+    if (!detach) {
+        migrate_fd_monitor_suspend(s, mon);
+    }
+
+    if (ret >= 0)
         migrate_fd_connect(s);
 
     return &s->mig_state;
-- 
1.6.5.2

[Qemu-devel] Re: [PATCH] Avoid permanently disabled QEMU monitor when UNIX migration fails

[Daniel P. Berrange]

On Fri, Dec 11, 2009 at 08:49:31PM +0000, Daniel P. Berrange wrote:
> If a UNIX migration command is attempt to a UNIX socket which does
> not exist, then the monitor is suspended, but never resumed. This
> prevents any further use of the monitor
> 
> * migration-unix.c: Only call migrate_fd_monitor_suspend() once
>   connected to the UNIX socket.

Sorry, forgot to include the signed-off tag with this patch, so will
resend.

FYI, the test case here is simply

   (qemu) migrate unix:/tmp/doesnotexist
   migration failed
   ...now hung, no prompt returns..


There is also similar kind of problem with exec migration, but I have not
been able to figure out where the problem lies for that one. I suspect 
something is not dealing with errors properly in the buffered file code.
If someone fancies investigating the exec: issue, the test case is simply
to run exec with a command that fails, eg give invalid syntax for one of 
its args. I discovered the problem when i did a simple typo with dd

   (qemu) migrate "exec:dd bs-1m of=/tmp/file"
   dd: unrecognized operand `bs-1m'
   Try `dd --help' for more information.
   ...now hung, no prompt returns..

Regards,
Daniel
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