[PULL 14/14] block: Convert 'block_resize' to coroutine

[Markus Armbruster]

From: Kevin Wolf <kwolf@redhat.com>

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>
Message-Id: <20201005155855.256490-15-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>
---
 qapi/block-core.json |  3 ++-
 blockdev.c           | 16 ++++++++--------
 hmp-commands.hx      |  1 +
 3 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/qapi/block-core.json b/qapi/block-core.json
index 3758ea9912..ee5ebef7f2 100644
--- a/qapi/block-core.json
+++ b/qapi/block-core.json
@@ -1310,7 +1310,8 @@
 { '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 a6ae475dac..fe6fb5dc1d 100644
--- a/blockdev.c
+++ b/blockdev.c
@@ -2449,14 +2449,14 @@ 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,
@@ -2466,9 +2466,6 @@ void qmp_block_resize(bool has_device, const char *device,
         return;
     }
 
-    aio_context = bdrv_get_aio_context(bs);
-    aio_context_acquire(aio_context);
-
     if (size < 0) {
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "size", "a >0 size");
         goto out;
@@ -2485,12 +2482,15 @@ void qmp_block_resize(bool has_device, const char 
*device,
     }
 
     bdrv_drained_begin(bs);
+    old_ctx = bdrv_co_enter(bs);
     blk_truncate(blk, size, false, PREALLOC_MODE_OFF, 0, errp);
+    bdrv_co_leave(bs, old_ctx);
     bdrv_drained_end(bs);
 
 out:
+    bdrv_co_lock(bs);
     blk_unref(blk);
-    aio_context_release(aio_context);
+    bdrv_co_unlock(bs);
 }
 
 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 e43ce600b8..cd068389de 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
-- 
2.26.2