[PATCH v6 12/12] block: Convert 'block_resize' to coroutine

[Kevin Wolf]

block_resize performs some I/O that could potentially take quite some
time, so use it as an example for the new 'coroutine': true annotation
in the QAPI schema.

bdrv_truncate() requires that we're already in the right AioContext for
the BlockDriverState if called in coroutine context. So instead of just
taking the AioContext lock, move the QMP handler coroutine to the
context.

Call blk_unref() only after switching back because blk_unref() may only
be called in the main thread.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 qapi/block-core.json |  3 ++-
 blockdev.c           | 13 ++++++-------
 hmp-commands.hx      |  1 +
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 6fbacddab2..a6003d8a92 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1291,7 +1291,8 @@
 { 'command': 'block_resize',
   'data': { '*device': 'str',
             '*node-name': 'str',
-            'size': 'int' } }
+            'size': 'int' },
+  'coroutine': true }
 
 ##
 # @NewImageMode:
diff --git a/blockdev.c b/blockdev.c
index 72df193ca7..9b9287b5d6 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2410,14 +2410,14 @@ BlockDirtyBitmapSha256 
*qmp_x_debug_block_dirty_bitmap_sha256(const char *node,
     return ret;
 }
 
-void qmp_block_resize(bool has_device, const char *device,
-                      bool has_node_name, const char *node_name,
-                      int64_t size, Error **errp)
+void coroutine_fn qmp_block_resize(bool has_device, const char *device,
+                                   bool has_node_name, const char *node_name,
+                                   int64_t size, Error **errp)
 {
     Error *local_err = NULL;
     BlockBackend *blk = NULL;
     BlockDriverState *bs;
-    AioContext *aio_context;
+    AioContext *old_ctx;
 
     bs = bdrv_lookup_bs(has_device ? device : NULL,
                         has_node_name ? node_name : NULL,
@@ -2427,8 +2427,7 @@ void qmp_block_resize(bool has_device, const char *device,
         return;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
+    old_ctx = bdrv_co_move_to_aio_context(bs);
 
     if (size < 0) {
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "size", "a >0 size");
@@ -2450,8 +2449,8 @@ void qmp_block_resize(bool has_device, const char *device,
     bdrv_drained_end(bs);
 
 out:
+    aio_co_reschedule_self(old_ctx);
     blk_unref(blk);
-    aio_context_release(aio_context);
 }
 
 void qmp_block_stream(bool has_job_id, const char *job_id, const char *device,
diff --git a/hmp-commands.hx b/hmp-commands.hx
index 7f0f3974ad..4e56fe08ca 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -76,6 +76,7 @@ ERST
         .params     = "device size",
         .help       = "resize a block image",
         .cmd        = hmp_block_resize,
+        .coroutine  = true,
     },
 
 SRST
-- 
2.25.4