[RFC] block/nbd: Move s->ioc on AioContext change

[Hanna Reitz]

s->ioc must always be attached to the NBD node's AioContext.  If that
context changes, s->ioc must be attached to the new context.

Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1990835
Signed-off-by: Hanna Reitz <hreitz@redhat.com>
---
This is an RFC because I believe there are some other things in the NBD
block driver that need attention on an AioContext change, too.  Namely,
there are two timers (reconnect_delay_timer and open_timer) that are
also attached to the node's AioContext, and I'm afraid they need to be
handled, too.  Probably pause them on detach, and resume them on attach,
but I'm not sure, which is why I'm posting this as an RFC to get some
comments from that from someone who knows this code better than me. :)

(Also, in a real v1, of course I'd want to add a regression test.)
---
 block/nbd.c | 28 ++++++++++++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/block/nbd.c b/block/nbd.c
index 63dbfa807d..119a774c04 100644
--- a/block/nbd.c
+++ b/block/nbd.c
@@ -2036,6 +2036,25 @@ static void nbd_cancel_in_flight(BlockDriverState *bs)
     nbd_co_establish_connection_cancel(s->conn);
 }
 
+static void nbd_attach_aio_context(BlockDriverState *bs,
+                                   AioContext *new_context)
+{
+    BDRVNBDState *s = bs->opaque;
+
+    if (s->ioc) {
+        qio_channel_attach_aio_context(s->ioc, new_context);
+    }
+}
+
+static void nbd_detach_aio_context(BlockDriverState *bs)
+{
+    BDRVNBDState *s = bs->opaque;
+
+    if (s->ioc) {
+        qio_channel_detach_aio_context(s->ioc);
+    }
+}
+
 static BlockDriver bdrv_nbd = {
     .format_name                = "nbd",
     .protocol_name              = "nbd",
@@ -2059,6 +2078,9 @@ static BlockDriver bdrv_nbd = {
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
+
+    .bdrv_attach_aio_context    = nbd_attach_aio_context,
+    .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static BlockDriver bdrv_nbd_tcp = {
@@ -2084,6 +2106,9 @@ static BlockDriver bdrv_nbd_tcp = {
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
+
+    .bdrv_attach_aio_context    = nbd_attach_aio_context,
+    .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static BlockDriver bdrv_nbd_unix = {
@@ -2109,6 +2134,9 @@ static BlockDriver bdrv_nbd_unix = {
     .bdrv_dirname               = nbd_dirname,
     .strong_runtime_opts        = nbd_strong_runtime_opts,
     .bdrv_cancel_in_flight      = nbd_cancel_in_flight,
+
+    .bdrv_attach_aio_context    = nbd_attach_aio_context,
+    .bdrv_detach_aio_context    = nbd_detach_aio_context,
 };
 
 static void bdrv_nbd_init(void)
-- 
2.34.1