block: add support for job pause/resume

Job pausing reuses the existing support for cancellable sleeps.  A pause
happens at the next sleeping point and lasts until the coroutine is
re-entered explicitly.  Cancellation was already doing a forced resume,
so implement it explicitly in terms of resume.

Paused jobs cannot be canceled without first resuming them.  This ensures
that I/O errors are never missed by management.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/blockdev.c b/blockdev.c
index 9a98ce9c89..612dd71f2d 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -1221,6 +1221,10 @@ void qmp_block_job_cancel(const char *device, Error **errp)
         error_set(errp, QERR_BLOCK_JOB_NOT_ACTIVE, device);
         return;
     }
+    if (job->paused) {
+        error_set(errp, QERR_BLOCK_JOB_PAUSED, device);
+        return;
+    }
 
     trace_qmp_block_job_cancel(job);
     block_job_cancel(job);