block: extend BLOCK_IO_ERROR event with nospace indicator

Management software, such as RHEV's vdsm, want to be able to allocate
disk space on demand. The basic use case is to start a VM with a small
disk and then the disk is enlarged when QEMU hits a ENOSPC condition.

To this end, the management software has to be notified when QEMU
encounters ENOSPC. The solution implemented by this commit is simple:
it extends the BLOCK_IO_ERROR with a 'nospace' key, which is true
when QEMU is stopped due to ENOSPC.

Note that support for querying this event is already present in
query-block by means of the 'io-status' key. Also, the new 'nospace'
BLOCK_IO_ERROR field shares the same semantics with 'io-status',
which basically means that werror= has to be set to either
'stop' or 'enospc' to enable 'nospace'.

Finally, this commit also updates the 'io-status' key doc in the
schema with a list of supported device models.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 14 insertions, 8 deletions

diff --git a/block.c b/block.c
index d06dd51632..460effe4fb 100644
--- a/block.c
+++ b/block.c
@@ -3639,6 +3639,18 @@ BlockErrorAction bdrv_get_error_action(BlockDriverState *bs, bool is_read, int e
     }
 }
 
+static void send_qmp_error_event(BlockDriverState *bs,
+                                 BlockErrorAction action,
+                                 bool is_read, int error)
+{
+    BlockErrorAction ac;
+
+    ac = is_read ? IO_OPERATION_TYPE_READ : IO_OPERATION_TYPE_WRITE;
+    qapi_event_send_block_io_error(bdrv_get_device_name(bs), ac, action,
+                                   bdrv_iostatus_is_enabled(bs),
+                                   error == ENOSPC, &error_abort);
+}
+
 /* This is done by device models because, while the block layer knows
  * about the error, it does not know whether an operation comes from
  * the device or the block layer (from a job, for example).
@@ -3664,16 +3676,10 @@ void bdrv_error_action(BlockDriverState *bs, BlockErrorAction action,
          * also ensures that the STOP/RESUME pair of events is emitted.
          */
         qemu_system_vmstop_request_prepare();
-        qapi_event_send_block_io_error(bdrv_get_device_name(bs),
-                                       is_read ? IO_OPERATION_TYPE_READ :
-                                       IO_OPERATION_TYPE_WRITE,
-                                       action, &error_abort);
+        send_qmp_error_event(bs, action, is_read, error);
         qemu_system_vmstop_request(RUN_STATE_IO_ERROR);
     } else {
-        qapi_event_send_block_io_error(bdrv_get_device_name(bs),
-                                       is_read ? IO_OPERATION_TYPE_READ :
-                                       IO_OPERATION_TYPE_WRITE,
-                                       action, &error_abort);
+        send_qmp_error_event(bs, action, is_read, error);
     }
 }