Re: [Qemu-devel] [PATCH v3 0/2] block: Quiesce old aio context during bdrv_set_aio_context

[Paolo Bonzini]

On 11/04/2017 00:04, Stefan Hajnoczi wrote:
> On Mon, Apr 10, 2017 at 10:26:34AM +0800, Fam Zheng wrote:
>> v3: Use bdrv_parent_drained_begin/end. [Kevin]
>>     Do it before releasing new_context. [Stefan]
>>
>> Fam Zheng (2):
>>   block: Make bdrv_parent_drained_begin/end public
>>   block: Quiesce old aio context during bdrv_set_aio_context
>>
>>  block.c               |  7 +++++--
>>  block/io.c            |  4 ++--
>>  include/block/block.h | 16 ++++++++++++++++
>>  3 files changed, 23 insertions(+), 4 deletions(-)
> 
> Thanks, applied to my block tree for 2.10:
> https://github.com/stefanha/qemu/commits/block
> 
> If you'd like this in a stable release please CC qemu-stable.

Stefan, can you squash this documentation patch in please?

diff --git a/block.c b/block.c
index 3b20a29..cb1c5c9 100644
--- a/block.c
+++ b/block.c
@@ -4392,6 +4392,18 @@ void bdrv_set_aio_context(BlockDriverState *bs,
AioContext *new_context)
 {
     AioContext *ctx = bdrv_get_aio_context(bs);

+    /* FIXME: This is the same as bdrv_drained_begin, only done
+     * manually.  At the end of this function, aio_enable_external
+     * must be done on ctx, not on new_context, so we cannot call
+     * bdrv_drained_end there.  And because bs->quiesce_counter will
+     * not be decreased there, we have to "explode" bdrv_drained_begin
+     * here too.
+     *
+     * Once aio_disable_external and aio_enable_external are replaced
+     * by BlockBackend device ops (called by .drained_begin/end
+     * BdrvChildRole callbacks), this can be replaced by a simple
+     * bdrv_drained_begin/end pair.
+     */
     aio_disable_external(ctx);
     bdrv_parent_drained_begin(bs);
     bdrv_drain(bs); /* ensure there are no in-flight requests */

Thanks,

Paolo