block: Keep track of devices' I/O status

This commit adds support to the BlockDriverState type to keep track
of devices' I/O status.

There are three possible status: BDRV_IOS_OK (no error), BDRV_IOS_ENOSPC
(no space error) and BDRV_IOS_FAILED (any other error). The distinction
between no space and other errors is important because a management
application may want to watch for no space in order to extend the
space assigned to the VM and put it to run again.

Qemu devices supporting the I/O status feature have to enable it
explicitly by calling bdrv_iostatus_enable() _and_ have to be
configured to stop the VM on errors (ie. werror=stop|enospc or
rerror=stop).

In case of multiple errors being triggered in sequence only the first
one is stored. The I/O status is always reset to BDRV_IOS_OK when the
'cont' command is issued.

Next commits will add support to some devices and extend the
query-block/info block commands to return the I/O status information.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 6 insertions, 0 deletions

diff --git a/monitor.c b/monitor.c
index 31b212aa6b..1a2895633e 100644
--- a/monitor.c
+++ b/monitor.c
@@ -1221,6 +1221,11 @@ struct bdrv_iterate_context {
     int err;
 };
 
+static void iostatus_bdrv_it(void *opaque, BlockDriverState *bs)
+{
+    bdrv_iostatus_reset(bs);
+}
+
 /**
  * do_cont(): Resume emulation.
  */
@@ -1237,6 +1242,7 @@ static int do_cont(Monitor *mon, const QDict *qdict, QObject **ret_data)
         return -1;
     }
 
+    bdrv_iterate(iostatus_bdrv_it, NULL);
     bdrv_iterate(encrypted_bdrv_it, &context);
     /* only resume the vm if all keys are set and valid */
     if (!context.err) {