Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] block: let blk_add/remove_aio_context_notifier() tolerate BDS changes
On 03/12/2018 06:27 AM, Stefan Hajnoczi wrote:
On Fri, Mar 09, 2018 at 09:56:44AM -0600, Eric Blake wrote:
On 03/06/2018 02:48 PM, Stefan Hajnoczi wrote:
Commit 2019ba0a0197 ("block: Add AioContextNotifier functions to BB")
added blk_add/remove_aio_context_notifier() and implemented them by
passing through the bdrv_*() equivalent.
This doesn't work across bdrv_append(), which detaches child->bs and
re-attaches it to a new BlockDriverState. When
blk_remove_aio_context_notifier() is called we will access the new BDS
instead of the one where the notifier was added!
From the point of view of the blk_*() API user, changes to the root BDS
should be transparent.
This patch maintains a list of AioContext notifiers in BlockBackend and
adds/removes them from the BlockDriverState as needed.
+typedef struct BlockBackendAioNotifier {
+void (*attached_aio_context)(AioContext *new_context, void *opaque);
+void (*detach_aio_context)(void *opaque);
Why the difference in tense (past 'attached' vs. present 'detach')?
The naming comes from the bdrv_add_aio_context_notifier() API:
void bdrv_add_aio_context_notifier(BlockDriverState *bs,
void (*attached_aio_context)(AioContext *new_context, void *opaque),
void (*detach_aio_context)(void *opaque), void *opaque)
It's "attached" because bs->aio_context has already been assigned before
the callback is invoked.
It's "detach" because the callback is invoked before bs->aio_context is
cleared.
Not great naming and I found it weird when I looked at the code too, but
at least this patch keeps the BlockBackend naming consistent with the
BlockDriverState naming.
Odd, but consistent, so I can live with it.
+
+QLIST_FOREACH(notifier, >aio_notifiers, list) {
+if (notifier->attached_aio_context == attached_aio_context &&
+notifier->detach_aio_context == detach_aio_context &&
+notifier->opaque == opaque) {
+QLIST_REMOVE(notifier, list);
Don't you need to use QLIST_FOREACH_SAFE if you are going to modify the list
during traversal?
It doesn't matter since we return right away:
g_free(notifier);
return;
Okay, makes sense (a safe iteration is required if you keep iterating
after action; but if you quit, the action has no impact on subsequent
iteration since there is no further iteration).
Reviewed-by: Eric Blake
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
Re: [Qemu-block] [Qemu-devel] [PATCH 1/2] block: let blk_add/remove_aio_context_notifier() tolerate BDS changes
On 03/06/2018 02:48 PM, Stefan Hajnoczi wrote:
Commit 2019ba0a0197 ("block: Add AioContextNotifier functions to BB")
added blk_add/remove_aio_context_notifier() and implemented them by
passing through the bdrv_*() equivalent.
This doesn't work across bdrv_append(), which detaches child->bs and
re-attaches it to a new BlockDriverState. When
blk_remove_aio_context_notifier() is called we will access the new BDS
instead of the one where the notifier was added!
From the point of view of the blk_*() API user, changes to the root BDS
should be transparent.
This patch maintains a list of AioContext notifiers in BlockBackend and
adds/removes them from the BlockDriverState as needed.
Reported-by: Stefano Panella
Cc: Max Reitz
Signed-off-by: Stefan Hajnoczi
---
block/block-backend.c | 63 +++
block/trace-events| 2 ++
2 files changed, 65 insertions(+)
diff --git a/block/block-backend.c b/block/block-backend.c
index 94ffbb6a60..aa27698820 100644
--- a/block/block-backend.c
+++ b/block/block-backend.c
@@ -31,6 +31,13 @@
static AioContext *blk_aiocb_get_aio_context(BlockAIOCB *acb);
+typedef struct BlockBackendAioNotifier {
+void (*attached_aio_context)(AioContext *new_context, void *opaque);
+void (*detach_aio_context)(void *opaque);
Why the difference in tense (past 'attached' vs. present 'detach')?
@@ -1827,12 +1877,25 @@ void blk_remove_aio_context_notifier(BlockBackend *blk,
void (*detach_aio_context)(void *),
void *opaque)
{
+BlockBackendAioNotifier *notifier;
BlockDriverState *bs = blk_bs(blk);
if (bs) {
bdrv_remove_aio_context_notifier(bs, attached_aio_context,
detach_aio_context, opaque);
}
+
+QLIST_FOREACH(notifier, >aio_notifiers, list) {
+if (notifier->attached_aio_context == attached_aio_context &&
+notifier->detach_aio_context == detach_aio_context &&
+notifier->opaque == opaque) {
+QLIST_REMOVE(notifier, list);
Don't you need to use QLIST_FOREACH_SAFE if you are going to modify the
list during traversal?
Otherwise makes sense to me.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3266
Virtualization: qemu.org | libvirt.org
