block: Use block_job_get() in find_block_job()

find_block_job() looks for a block backend with a specified name,
checks whether it has a block job and acquires its AioContext.

We want to identify jobs by their ID and not by the block backend
they're attached to, so this patch ignores the backends altogether and
gets the job directly. Apart from making the code simpler, this will
allow us to find block jobs once they start having user-specified IDs.

To ensure backward compatibility we keep ERROR_CLASS_DEVICE_NOT_ACTIVE
as the error class if the job doesn't exist. In subsequent patches
we'll also need to keep the device name as the default job ID if the
user doesn't specify a different one.

Signed-off-by: Alberto Garcia <berto@igalia.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

blockdev.c

@@ -3704,42 +3704,28 @@ void qmp_blockdev_mirror(const char *device, const char *target,
     aio_context_release(aio_context);
 }
 
-/* Get the block job for a given device name and acquire its AioContext */
-static BlockJob *find_block_job(const char *device, AioContext **aio_context,
+/* Get a block job using its ID and acquire its AioContext */
+static BlockJob *find_block_job(const char *id, AioContext **aio_context,
                                 Error **errp)
 {
-    BlockBackend *blk;
-    BlockDriverState *bs;
+    BlockJob *job;
 
-    *aio_context = NULL;
+    assert(id != NULL);
 
-    blk = blk_by_name(device);
-    if (!blk) {
-        goto notfound;
-    }
-
-    *aio_context = blk_get_aio_context(blk);
-    aio_context_acquire(*aio_context);
+    *aio_context = NULL;
 
-    if (!blk_is_available(blk)) {
-        goto notfound;
-    }
-    bs = blk_bs(blk);
+    job = block_job_get(id);
 
-    if (!bs->job) {
-        goto notfound;
+    if (!job) {
+        error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
+                  "Block job '%s' not found", id);
+        return NULL;
     }
 
-    return bs->job;
+    *aio_context = blk_get_aio_context(job->blk);
+    aio_context_acquire(*aio_context);
 
-notfound:
-    error_set(errp, ERROR_CLASS_DEVICE_NOT_ACTIVE,
-              "No active block job on device '%s'", device);
-    if (*aio_context) {
-        aio_context_release(*aio_context);
-        *aio_context = NULL;
-    }
-    return NULL;
+    return job;
 }
 
 void qmp_block_job_set_speed(const char *device, int64_t speed, Error **errp)