[Qemu-devel] [RFC 5/5] nbd: Follow the BDS' AIO context

[Max Reitz]

Keep the NBD server always in the same AIO context as the exported BDS
by calling bdrv_follow_aio() and implementing the required callbacks.

Signed-off-by: Max Reitz <address@hidden>
---
 nbd.c | 36 ++++++++++++++++++++++++++++++++----
 1 file changed, 32 insertions(+), 4 deletions(-)

diff --git a/nbd.c b/nbd.c
index 803b3d7..1898c5e 100644
--- a/nbd.c
+++ b/nbd.c
@@ -808,6 +808,36 @@ static void nbd_request_put(NBDRequest *req)
     nbd_client_put(client);
 }
 
+static int nbd_can_read(void *opaque);
+static void nbd_read(void *opaque);
+static void nbd_restart_write(void *opaque);
+
+static void bs_aio_attach(AioContext *ctx, void *opaque)
+{
+    NBDExport *exp = opaque;
+    NBDClient *client;
+
+    QTAILQ_FOREACH(client, &exp->clients, next) {
+        aio_set_fd_handler2(ctx, client->sock,
+                            nbd_can_read, nbd_read, NULL, client);
+    }
+
+    exp->ctx = ctx;
+}
+
+static void bs_aio_detach(void *opaque)
+{
+    NBDExport *exp = opaque;
+    NBDClient *client;
+
+    QTAILQ_FOREACH(client, &exp->clients, next) {
+        aio_set_fd_handler2(exp->ctx, client->sock,
+                            NULL, NULL, NULL, NULL);
+    }
+
+    exp->ctx = NULL;
+}
+
 NBDExport *nbd_export_new(BlockDriverState *bs, off_t dev_offset,
                           off_t size, uint32_t nbdflags,
                           void (*close)(NBDExport *))
@@ -822,6 +852,7 @@ NBDExport *nbd_export_new(BlockDriverState *bs, off_t 
dev_offset,
     exp->close = close;
     exp->ctx = bdrv_get_aio_context(bs);
     bdrv_ref(bs);
+    bdrv_follow_aio(bs, bs_aio_attach, bs_aio_detach, exp);
     return exp;
 }
 
@@ -869,6 +900,7 @@ void nbd_export_close(NBDExport *exp)
     nbd_export_set_name(exp, NULL);
     nbd_export_put(exp);
     if (exp->bs) {
+        bdrv_unfollow_aio(exp->bs, bs_aio_attach, bs_aio_detach, exp);
         bdrv_unref(exp->bs);
         exp->bs = NULL;
     }
@@ -912,10 +944,6 @@ void nbd_export_close_all(void)
     }
 }
 
-static int nbd_can_read(void *opaque);
-static void nbd_read(void *opaque);
-static void nbd_restart_write(void *opaque);
-
 static ssize_t nbd_co_send_reply(NBDRequest *req, struct nbd_reply *reply,
                                  int len)
 {
-- 
1.9.3