NBD patches for 2023-09-07

- Andrey Drobyshev - fix regression in iotest 197 under -nbd
 - Stefan Hajnoczi - allow coroutine read and write context to split
 across threads
 - Philippe Mathieu-Daudé - remove a VLA allocation
 - Denis V. Lunev - fix regression in iotest 233 with qemu-nbd -v --fork
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 PeTycAwND6cMKYlKMyEzcJXv9IdRBw==
 =jAZi
 -----END PGP SIGNATURE-----

Merge tag 'pull-nbd-2023-09-07-v2' of https://repo.or.cz/qemu/ericb into staging

NBD patches for 2023-09-07

- Andrey Drobyshev - fix regression in iotest 197 under -nbd
- Stefan Hajnoczi - allow coroutine read and write context to split
across threads
- Philippe Mathieu-Daudé - remove a VLA allocation
- Denis V. Lunev - fix regression in iotest 233 with qemu-nbd -v --fork

# -----BEGIN PGP SIGNATURE-----
#
# iQEzBAABCAAdFiEEccLMIrHEYCkn0vOqp6FrSiUnQ2oFAmT7EsUACgkQp6FrSiUn
# Q2qiKgf9EqCWPmcsH2nvXrDvZmDc0/I4tineaNY+hSdPtSb6RFA1IH8AvzkrkPYU
# 9ojX6QFp1Z30fUs+pwweQhBMYta03QyjCFhsbPRmDq391dtIDCeww3o+RD1kw/pg
# 2ZC+P9N1U3pi2Hi8FhxH17GYYgOQnHMKM9gt1V7JOQvFsDFWbTo9sFj8p/BPoWxV
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# Y5imM/PbyCqRKQ6MYyJenVk4QVTe1IKO6D4vf1ZHLDBEiaw9NaeYHlk6lnDC4O9v
# PeTycAwND6cMKYlKMyEzcJXv9IdRBw==
# =jAZi
# -----END PGP SIGNATURE-----
# gpg: Signature made Fri 08 Sep 2023 08:25:41 EDT
# gpg:                using RSA key 71C2CC22B1C4602927D2F3AAA7A16B4A2527436A
# gpg: Good signature from "Eric Blake <eblake@redhat.com>" [full]
# gpg:                 aka "Eric Blake (Free Software Programmer) <ebb9@byu.net>" [full]
# gpg:                 aka "[jpeg image of size 6874]" [full]
# Primary key fingerprint: 71C2 CC22 B1C4 6029 27D2  F3AA A7A1 6B4A 2527 436A

* tag 'pull-nbd-2023-09-07-v2' of https://repo.or.cz/qemu/ericb:
  qemu-nbd: document -v behavior in respect to --fork in man
  qemu-nbd: Restore "qemu-nbd -v --fork" output
  qemu-nbd: invent nbd_client_release_pipe() helper
  qemu-nbd: put saddr into into struct NbdClientOpts
  qemu-nbd: move srcpath into struct NbdClientOpts
  qemu-nbd: define struct NbdClientOpts when HAVE_NBD_DEVICE is not defined
  qemu-nbd: improve error message for dup2 error
  util/iov: Avoid dynamic stack allocation
  io: follow coroutine AioContext in qio_channel_yield()
  io: check there are no qio_channel_yield() coroutines during ->finalize()
  nbd: drop unused nbd_start_negotiate() aio_context argument
  nbd: drop unused nbd_receive_negotiate() aio_context argument
  qemu-iotests/197: use more generic commands for formats other than qcow2

Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/nbd.c

@@ -352,7 +352,7 @@ int coroutine_fn nbd_co_do_establish_connection(BlockDriverState *bs,
     }
 
     qio_channel_set_blocking(s->ioc, false, NULL);
-    qio_channel_attach_aio_context(s->ioc, bdrv_get_aio_context(bs));
+    qio_channel_set_follow_coroutine_ctx(s->ioc, true);
 
     /* successfully connected */
     WITH_QEMU_LOCK_GUARD(&s->requests_lock) {
@@ -397,7 +397,6 @@ static void coroutine_fn GRAPH_RDLOCK nbd_reconnect_attempt(BDRVNBDState *s)
 
     /* Finalize previous connection if any */
     if (s->ioc) {
-        qio_channel_detach_aio_context(s->ioc);
         yank_unregister_function(BLOCKDEV_YANK_INSTANCE(s->bs->node_name),
                                  nbd_yank, s->bs);
         object_unref(OBJECT(s->ioc));
@@ -2089,10 +2088,6 @@ static void nbd_attach_aio_context(BlockDriverState *bs,
      * the reconnect_delay_timer cannot be active here.
      */
     assert(!s->reconnect_delay_timer);
-
-    if (s->ioc) {
-        qio_channel_attach_aio_context(s->ioc, new_context);
-    }
 }
 
 static void nbd_detach_aio_context(BlockDriverState *bs)
@@ -2101,10 +2096,6 @@ static void nbd_detach_aio_context(BlockDriverState *bs)
 
     assert(!s->open_timer);
     assert(!s->reconnect_delay_timer);
-
-    if (s->ioc) {
-        qio_channel_detach_aio_context(s->ioc);
-    }
 }
 
 static BlockDriver bdrv_nbd = {

docs/tools/qemu-nbd.rst

@@ -197,7 +197,9 @@ driver options if :option:`--image-opts` is specified.
 
 .. option:: -v, --verbose
 
-  Display extra debugging information.
+  Display extra debugging information. This option also keeps the original
+  *STDERR* stream open if the ``qemu-nbd`` process is daemonized due to
+  other options like :option:`--fork` or :option:`-c`.
 
 .. option:: -h, --help
 

include/block/nbd.h

@@ -324,8 +324,7 @@ typedef struct NBDExportInfo {
     char **contexts;
 } NBDExportInfo;
 
-int nbd_receive_negotiate(AioContext *aio_context, QIOChannel *ioc,
+int nbd_receive_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
-                          QCryptoTLSCreds *tlscreds,
                           const char *hostname, QIOChannel **outioc,
                           NBDExportInfo *info, Error **errp);
 void nbd_free_export_list(NBDExportInfo *info, int count);

include/io/channel-util.h

@@ -49,4 +49,27 @@
 QIOChannel *qio_channel_new_fd(int fd,
                                Error **errp);
 
+/**
+ * qio_channel_util_set_aio_fd_handler:
+ * @read_fd: the file descriptor for the read handler
+ * @read_ctx: the AioContext for the read handler
+ * @io_read: the read handler
+ * @write_fd: the file descriptor for the write handler
+ * @write_ctx: the AioContext for the write handler
+ * @io_write: the write handler
+ * @opaque: the opaque argument to the read and write handler
+ *
+ * Set the read and write handlers when @read_ctx and @write_ctx are non-NULL,
+ * respectively. To leave a handler in its current state, pass a NULL
+ * AioContext. To clear a handler, pass a non-NULL AioContext and a NULL
+ * handler.
+ */
+void qio_channel_util_set_aio_fd_handler(int read_fd,
+                                         AioContext *read_ctx,
+                                         IOHandler *io_read,
+                                         int write_fd,
+                                         AioContext *write_ctx,
+                                         IOHandler *io_write,
+                                         void *opaque);
+
 #endif /* QIO_CHANNEL_UTIL_H */

include/io/channel.h

@@ -81,9 +81,11 @@ struct QIOChannel {
     Object parent;
     unsigned int features; /* bitmask of QIOChannelFeatures */
     char *name;
-    AioContext *ctx;
+    AioContext *read_ctx;
     Coroutine *read_coroutine;
+    AioContext *write_ctx;
     Coroutine *write_coroutine;
+    bool follow_coroutine_ctx;
 #ifdef _WIN32
     HANDLE event; /* For use with GSource on Win32 */
 #endif
@@ -140,8 +142,9 @@ struct QIOChannelClass {
                      int whence,
                      Error **errp);
     void (*io_set_aio_fd_handler)(QIOChannel *ioc,
-                                  AioContext *ctx,
+                                  AioContext *read_ctx,
                                   IOHandler *io_read,
+                                  AioContext *write_ctx,
                                   IOHandler *io_write,
                                   void *opaque);
     int (*io_flush)(QIOChannel *ioc,
@@ -498,6 +501,21 @@ int qio_channel_set_blocking(QIOChannel *ioc,
                              bool enabled,
                              Error **errp);
 
+/**
+ * qio_channel_set_follow_coroutine_ctx:
+ * @ioc: the channel object
+ * @enabled: whether or not to follow the coroutine's AioContext
+ *
+ * If @enabled is true, calls to qio_channel_yield() use the current
+ * coroutine's AioContext. Usually this is desirable.
+ *
+ * If @enabled is false, calls to qio_channel_yield() use the global iohandler
+ * AioContext. This is may be used by coroutines that run in the main loop and
+ * do not wish to respond to I/O during nested event loops. This is the
+ * default for compatibility with code that is not aware of AioContexts.
+ */
+void qio_channel_set_follow_coroutine_ctx(QIOChannel *ioc, bool enabled);
+
 /**
  * qio_channel_close:
  * @ioc: the channel object
@@ -703,41 +721,6 @@ GSource *qio_channel_add_watch_source(QIOChannel *ioc,
                                       GDestroyNotify notify,
                                       GMainContext *context);
 
-/**
- * qio_channel_attach_aio_context:
- * @ioc: the channel object
- * @ctx: the #AioContext to set the handlers on
- *
- * Request that qio_channel_yield() sets I/O handlers on
- * the given #AioContext.  If @ctx is %NULL, qio_channel_yield()
- * uses QEMU's main thread event loop.
- *
- * You can move a #QIOChannel from one #AioContext to another even if
- * I/O handlers are set for a coroutine.  However, #QIOChannel provides
- * no synchronization between the calls to qio_channel_yield() and
- * qio_channel_attach_aio_context().
- *
- * Therefore you should first call qio_channel_detach_aio_context()
- * to ensure that the coroutine is not entered concurrently.  Then,
- * while the coroutine has yielded, call qio_channel_attach_aio_context(),
- * and then aio_co_schedule() to place the coroutine on the new
- * #AioContext.  The calls to qio_channel_detach_aio_context()
- * and qio_channel_attach_aio_context() should be protected with
- * aio_context_acquire() and aio_context_release().
- */
-void qio_channel_attach_aio_context(QIOChannel *ioc,
-                                    AioContext *ctx);
-
-/**
- * qio_channel_detach_aio_context:
- * @ioc: the channel object
- *
- * Disable any I/O handlers set by qio_channel_yield().  With the
- * help of aio_co_schedule(), this allows moving a coroutine that was
- * paused by qio_channel_yield() to another context.
- */
-void qio_channel_detach_aio_context(QIOChannel *ioc);
-
 /**
  * qio_channel_yield:
  * @ioc: the channel object
@@ -785,8 +768,9 @@ void qio_channel_wait(QIOChannel *ioc,
 /**
  * qio_channel_set_aio_fd_handler:
  * @ioc: the channel object
- * @ctx: the AioContext to set the handlers on
+ * @read_ctx: the AioContext to set the read handler on or NULL
  * @io_read: the read handler
+ * @write_ctx: the AioContext to set the write handler on or NULL
  * @io_write: the write handler
  * @opaque: the opaque value passed to the handler
  *
@@ -794,10 +778,17 @@ void qio_channel_wait(QIOChannel *ioc,
  * be used by channel implementations to forward the handlers
  * to another channel (e.g. from #QIOChannelTLS to the
  * underlying socket).
+ *
+ * When @read_ctx is NULL, don't touch the read handler. When @write_ctx is
+ * NULL, don't touch the write handler. Note that setting the read handler
+ * clears the write handler, and vice versa, if they share the same AioContext.
+ * Therefore the caller must pass both handlers together when sharing the same
+ * AioContext.
  */
 void qio_channel_set_aio_fd_handler(QIOChannel *ioc,
-                                    AioContext *ctx,
+                                    AioContext *read_ctx,
                                     IOHandler *io_read,
+                                    AioContext *write_ctx,
                                     IOHandler *io_write,
                                     void *opaque);
 

include/qemu/vhost-user-server.h

@@ -43,6 +43,7 @@ typedef struct {
     unsigned int in_flight; /* atomic */
 
     /* Protected by ctx lock */
+    bool in_qio_channel_yield;
     bool wait_idle;
     VuDev vu_dev;
     QIOChannel *ioc; /* The I/O channel with the client */

io/channel-command.c

@@ -20,6 +20,7 @@
 
 #include "qemu/osdep.h"
 #include "io/channel-command.h"
+#include "io/channel-util.h"
 #include "io/channel-watch.h"
 #include "qapi/error.h"
 #include "qemu/module.h"
@@ -331,14 +332,17 @@ static int qio_channel_command_close(QIOChannel *ioc,
 
 
 static void qio_channel_command_set_aio_fd_handler(QIOChannel *ioc,
-                                                   AioContext *ctx,
+                                                   AioContext *read_ctx,
                                                    IOHandler *io_read,
+                                                   AioContext *write_ctx,
                                                    IOHandler *io_write,
                                                    void *opaque)
 {
     QIOChannelCommand *cioc = QIO_CHANNEL_COMMAND(ioc);
-    aio_set_fd_handler(ctx, cioc->readfd, io_read, NULL, NULL, NULL, opaque);
+
-    aio_set_fd_handler(ctx, cioc->writefd, NULL, io_write, NULL, NULL, opaque);
+    qio_channel_util_set_aio_fd_handler(cioc->readfd, read_ctx, io_read,
+                                        cioc->writefd, write_ctx, io_write,
+                                        opaque);
 }
 
 

io/channel-file.c

@@ -20,6 +20,7 @@
 
 #include "qemu/osdep.h"
 #include "io/channel-file.h"
+#include "io/channel-util.h"
 #include "io/channel-watch.h"
 #include "qapi/error.h"
 #include "qemu/module.h"
@@ -192,13 +193,17 @@ static int qio_channel_file_close(QIOChannel *ioc,
 
 
 static void qio_channel_file_set_aio_fd_handler(QIOChannel *ioc,
-                                                AioContext *ctx,
+                                                AioContext *read_ctx,
                                                 IOHandler *io_read,
+                                                AioContext *write_ctx,
                                                 IOHandler *io_write,
                                                 void *opaque)
 {
     QIOChannelFile *fioc = QIO_CHANNEL_FILE(ioc);
-    aio_set_fd_handler(ctx, fioc->fd, io_read, io_write, NULL, NULL, opaque);
+
+    qio_channel_util_set_aio_fd_handler(fioc->fd, read_ctx, io_read,
+                                        fioc->fd, write_ctx, io_write,
+                                        opaque);
 }
 
 static GSource *qio_channel_file_create_watch(QIOChannel *ioc,

io/channel-null.c

@@ -128,8 +128,9 @@ qio_channel_null_close(QIOChannel *ioc,
 
 static void
 qio_channel_null_set_aio_fd_handler(QIOChannel *ioc G_GNUC_UNUSED,
-                                    AioContext *ctx G_GNUC_UNUSED,
+                                    AioContext *read_ctx G_GNUC_UNUSED,
                                     IOHandler *io_read G_GNUC_UNUSED,
+                                    AioContext *write_ctx G_GNUC_UNUSED,
                                     IOHandler *io_write G_GNUC_UNUSED,
                                     void *opaque G_GNUC_UNUSED)
 {

io/channel-socket.c

@@ -22,6 +22,7 @@
 #include "qapi/qapi-visit-sockets.h"
 #include "qemu/module.h"
 #include "io/channel-socket.h"
+#include "io/channel-util.h"
 #include "io/channel-watch.h"
 #include "trace.h"
 #include "qapi/clone-visitor.h"
@@ -893,13 +894,17 @@ qio_channel_socket_shutdown(QIOChannel *ioc,
 }
 
 static void qio_channel_socket_set_aio_fd_handler(QIOChannel *ioc,
-                                                  AioContext *ctx,
+                                                  AioContext *read_ctx,
                                                   IOHandler *io_read,
+                                                  AioContext *write_ctx,
                                                   IOHandler *io_write,
                                                   void *opaque)
 {
     QIOChannelSocket *sioc = QIO_CHANNEL_SOCKET(ioc);
-    aio_set_fd_handler(ctx, sioc->fd, io_read, io_write, NULL, NULL, opaque);
+
+    qio_channel_util_set_aio_fd_handler(sioc->fd, read_ctx, io_read,
+                                        sioc->fd, write_ctx, io_write,
+                                        opaque);
 }
 
 static GSource *qio_channel_socket_create_watch(QIOChannel *ioc,

io/channel-tls.c

@@ -388,14 +388,16 @@ static int qio_channel_tls_close(QIOChannel *ioc,
 }
 
 static void qio_channel_tls_set_aio_fd_handler(QIOChannel *ioc,
-                                               AioContext *ctx,
+                                               AioContext *read_ctx,
                                                IOHandler *io_read,
+                                               AioContext *write_ctx,
                                                IOHandler *io_write,
                                                void *opaque)
 {
     QIOChannelTLS *tioc = QIO_CHANNEL_TLS(ioc);
 
-    qio_channel_set_aio_fd_handler(tioc->master, ctx, io_read, io_write, opaque);
+    qio_channel_set_aio_fd_handler(tioc->master, read_ctx, io_read,
+            write_ctx, io_write, opaque);
 }
 
 typedef struct QIOChannelTLSSource QIOChannelTLSSource;

io/channel-util.c

@@ -36,3 +36,27 @@ QIOChannel *qio_channel_new_fd(int fd,
     }
     return ioc;
 }
+
+
+void qio_channel_util_set_aio_fd_handler(int read_fd,
+                                         AioContext *read_ctx,
+                                         IOHandler *io_read,
+                                         int write_fd,
+                                         AioContext *write_ctx,
+                                         IOHandler *io_write,
+                                         void *opaque)
+{
+    if (read_fd == write_fd && read_ctx == write_ctx) {
+        aio_set_fd_handler(read_ctx, read_fd, io_read, io_write,
+                NULL, NULL, opaque);
+    } else {
+        if (read_ctx) {
+            aio_set_fd_handler(read_ctx, read_fd, io_read, NULL,
+                    NULL, NULL, opaque);
+        }
+        if (write_ctx) {
+            aio_set_fd_handler(write_ctx, write_fd, NULL, io_write,
+                    NULL, NULL, opaque);
+        }
+    }
+}

io/channel.c

@@ -365,6 +365,12 @@ int qio_channel_set_blocking(QIOChannel *ioc,
 }
 
 
+void qio_channel_set_follow_coroutine_ctx(QIOChannel *ioc, bool enabled)
+{
+    ioc->follow_coroutine_ctx = enabled;
+}
+
+
 int qio_channel_close(QIOChannel *ioc,
                       Error **errp)
 {
@@ -388,14 +394,16 @@ GSource *qio_channel_create_watch(QIOChannel *ioc,
 
 
 void qio_channel_set_aio_fd_handler(QIOChannel *ioc,
-                                    AioContext *ctx,
+                                    AioContext *read_ctx,
                                     IOHandler *io_read,
+                                    AioContext *write_ctx,
                                     IOHandler *io_write,
                                     void *opaque)
 {
     QIOChannelClass *klass = QIO_CHANNEL_GET_CLASS(ioc);
 
-    klass->io_set_aio_fd_handler(ioc, ctx, io_read, io_write, opaque);
+    klass->io_set_aio_fd_handler(ioc, read_ctx, io_read, write_ctx, io_write,
+            opaque);
 }
 
 guint qio_channel_add_watch_full(QIOChannel *ioc,
@@ -542,56 +550,101 @@ static void qio_channel_restart_write(void *opaque)
     aio_co_wake(co);
 }
 
-static void qio_channel_set_aio_fd_handlers(QIOChannel *ioc)
+static void coroutine_fn
+qio_channel_set_fd_handlers(QIOChannel *ioc, GIOCondition condition)
 {
-    IOHandler *rd_handler = NULL, *wr_handler = NULL;
+    AioContext *ctx = ioc->follow_coroutine_ctx ?
+        qemu_coroutine_get_aio_context(qemu_coroutine_self()) :
+        iohandler_get_aio_context();
+    AioContext *read_ctx = NULL;
+    IOHandler *io_read = NULL;
+    AioContext *write_ctx = NULL;
+    IOHandler *io_write = NULL;
+
+    if (condition == G_IO_IN) {
+        ioc->read_coroutine = qemu_coroutine_self();
+        ioc->read_ctx = ctx;
+        read_ctx = ctx;
+        io_read = qio_channel_restart_read;
+
+        /*
+         * Thread safety: if the other coroutine is set and its AioContext
+         * matches ours, then there is mutual exclusion between read and write
+         * because they share a single thread and it's safe to set both read
+         * and write fd handlers here. If the AioContext does not match ours,
+         * then both threads may run in parallel but there is no shared state
+         * to worry about.
+         */
+        if (ioc->write_coroutine && ioc->write_ctx == ctx) {
+            write_ctx = ctx;
+            io_write = qio_channel_restart_write;
+        }
+    } else if (condition == G_IO_OUT) {
+        ioc->write_coroutine = qemu_coroutine_self();
+        ioc->write_ctx = ctx;
+        write_ctx = ctx;
+        io_write = qio_channel_restart_write;
+        if (ioc->read_coroutine && ioc->read_ctx == ctx) {
+            read_ctx = ctx;
+            io_read = qio_channel_restart_read;
+        }
+    } else {
+        abort();
+    }
+
+    qio_channel_set_aio_fd_handler(ioc, read_ctx, io_read,
+            write_ctx, io_write, ioc);
+}
+
+static void coroutine_fn
+qio_channel_clear_fd_handlers(QIOChannel *ioc, GIOCondition condition)
+{
+    AioContext *read_ctx = NULL;
+    IOHandler *io_read = NULL;
+    AioContext *write_ctx = NULL;
+    IOHandler *io_write = NULL;
     AioContext *ctx;
 
-    if (ioc->read_coroutine) {
+    if (condition == G_IO_IN) {
-        rd_handler = qio_channel_restart_read;
+        ctx = ioc->read_ctx;
+        read_ctx = ctx;
+        io_read = NULL;
+        if (ioc->write_coroutine && ioc->write_ctx == ctx) {
+            write_ctx = ctx;
+            io_write = qio_channel_restart_write;
         }
-    if (ioc->write_coroutine) {
+    } else if (condition == G_IO_OUT) {
-        wr_handler = qio_channel_restart_write;
+        ctx = ioc->write_ctx;
+        write_ctx = ctx;
+        io_write = NULL;
+        if (ioc->read_coroutine && ioc->read_ctx == ctx) {
+            read_ctx = ctx;
+            io_read = qio_channel_restart_read;
+        }
+    } else {
+        abort();
     }
 
-    ctx = ioc->ctx ? ioc->ctx : iohandler_get_aio_context();
+    qio_channel_set_aio_fd_handler(ioc, read_ctx, io_read,
-    qio_channel_set_aio_fd_handler(ioc, ctx, rd_handler, wr_handler, ioc);
+            write_ctx, io_write, ioc);
-}
-
-void qio_channel_attach_aio_context(QIOChannel *ioc,
-                                    AioContext *ctx)
-{
-    assert(!ioc->read_coroutine);
-    assert(!ioc->write_coroutine);
-    ioc->ctx = ctx;
-}
-
-void qio_channel_detach_aio_context(QIOChannel *ioc)
-{
-    ioc->read_coroutine = NULL;
-    ioc->write_coroutine = NULL;
-    qio_channel_set_aio_fd_handlers(ioc);
-    ioc->ctx = NULL;
 }
 
 void coroutine_fn qio_channel_yield(QIOChannel *ioc,
                                     GIOCondition condition)
 {
-    AioContext *ioc_ctx = ioc->ctx ?: qemu_get_aio_context();
+    AioContext *ioc_ctx;
 
     assert(qemu_in_coroutine());
-    assert(in_aio_context_home_thread(ioc_ctx));
+    ioc_ctx = qemu_coroutine_get_aio_context(qemu_coroutine_self());
 
     if (condition == G_IO_IN) {
         assert(!ioc->read_coroutine);
-        ioc->read_coroutine = qemu_coroutine_self();
     } else if (condition == G_IO_OUT) {
         assert(!ioc->write_coroutine);
-        ioc->write_coroutine = qemu_coroutine_self();
     } else {
         abort();
     }
-    qio_channel_set_aio_fd_handlers(ioc);
+    qio_channel_set_fd_handlers(ioc, condition);
     qemu_coroutine_yield();
     assert(in_aio_context_home_thread(ioc_ctx));
 
@@ -599,11 +652,10 @@ void coroutine_fn qio_channel_yield(QIOChannel *ioc,
      * through the aio_fd_handlers. */
     if (condition == G_IO_IN) {
         assert(ioc->read_coroutine == NULL);
-        qio_channel_set_aio_fd_handlers(ioc);
     } else if (condition == G_IO_OUT) {
         assert(ioc->write_coroutine == NULL);
-        qio_channel_set_aio_fd_handlers(ioc);
     }
+    qio_channel_clear_fd_handlers(ioc, condition);
 }
 
 void qio_channel_wake_read(QIOChannel *ioc)
@@ -653,6 +705,10 @@ static void qio_channel_finalize(Object *obj)
 {
     QIOChannel *ioc = QIO_CHANNEL(obj);
 
+    /* Must not have coroutines in qio_channel_yield() */
+    assert(!ioc->read_coroutine);
+    assert(!ioc->write_coroutine);
+
     g_free(ioc->name);
 
 #ifdef _WIN32

migration/channel-block.c

@@ -158,8 +158,9 @@ qio_channel_block_close(QIOChannel *ioc,
 
 static void
 qio_channel_block_set_aio_fd_handler(QIOChannel *ioc,
-                                     AioContext *ctx,
+                                     AioContext *read_ctx,
                                      IOHandler *io_read,
+                                     AioContext *write_ctx,
                                      IOHandler *io_write,
                                      void *opaque)
 {

migration/rdma.c

@@ -3103,22 +3103,23 @@ static GSource *qio_channel_rdma_create_watch(QIOChannel *ioc,
 }
 
 static void qio_channel_rdma_set_aio_fd_handler(QIOChannel *ioc,
-                                                  AioContext *ctx,
+                                                AioContext *read_ctx,
                                                 IOHandler *io_read,
+                                                AioContext *write_ctx,
                                                 IOHandler *io_write,
                                                 void *opaque)
 {
     QIOChannelRDMA *rioc = QIO_CHANNEL_RDMA(ioc);
     if (io_read) {
-        aio_set_fd_handler(ctx, rioc->rdmain->recv_comp_channel->fd, io_read,
+        aio_set_fd_handler(read_ctx, rioc->rdmain->recv_comp_channel->fd,
-                           io_write, NULL, NULL, opaque);
+                           io_read, io_write, NULL, NULL, opaque);
-        aio_set_fd_handler(ctx, rioc->rdmain->send_comp_channel->fd, io_read,
+        aio_set_fd_handler(read_ctx, rioc->rdmain->send_comp_channel->fd,
-                           io_write, NULL, NULL, opaque);
+                           io_read, io_write, NULL, NULL, opaque);
     } else {
-        aio_set_fd_handler(ctx, rioc->rdmaout->recv_comp_channel->fd, io_read,
+        aio_set_fd_handler(write_ctx, rioc->rdmaout->recv_comp_channel->fd,
-                           io_write, NULL, NULL, opaque);
+                           io_read, io_write, NULL, NULL, opaque);
-        aio_set_fd_handler(ctx, rioc->rdmaout->send_comp_channel->fd, io_read,
+        aio_set_fd_handler(write_ctx, rioc->rdmaout->send_comp_channel->fd,
-                           io_write, NULL, NULL, opaque);
+                           io_read, io_write, NULL, NULL, opaque);
     }
 }
 

nbd/client-connection.c

@@ -146,8 +146,7 @@ static int nbd_connect(QIOChannelSocket *sioc, SocketAddress *addr,
         return 0;
     }
 
-    ret = nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc), tlscreds,
+    ret = nbd_receive_negotiate(QIO_CHANNEL(sioc), tlscreds, tlshostname,
-                                tlshostname,
                                 outioc, info, errp);
     if (ret < 0) {
         /*

nbd/client.c

@@ -877,8 +877,7 @@ static int nbd_list_meta_contexts(QIOChannel *ioc,
  * Returns: negative errno: failure talking to server
  *          non-negative: enum NBDMode describing server abilities
  */
-static int nbd_start_negotiate(AioContext *aio_context, QIOChannel *ioc,
+static int nbd_start_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
-                               QCryptoTLSCreds *tlscreds,
                                const char *hostname, QIOChannel **outioc,
                                bool structured_reply, bool *zeroes,
                                Error **errp)
@@ -946,10 +945,6 @@ static int nbd_start_negotiate(AioContext *aio_context, QIOChannel *ioc,
                     return -EINVAL;
                 }
                 ioc = *outioc;
-                if (aio_context) {
-                    qio_channel_set_blocking(ioc, false, NULL);
-                    qio_channel_attach_aio_context(ioc, aio_context);
-                }
             } else {
                 error_setg(errp, "Server does not support STARTTLS");
                 return -EINVAL;
@@ -1014,8 +1009,7 @@ static int nbd_negotiate_finish_oldstyle(QIOChannel *ioc, NBDExportInfo *info,
  * Returns: negative errno: failure talking to server
  *          0: server is connected
  */
-int nbd_receive_negotiate(AioContext *aio_context, QIOChannel *ioc,
+int nbd_receive_negotiate(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
-                          QCryptoTLSCreds *tlscreds,
                           const char *hostname, QIOChannel **outioc,
                           NBDExportInfo *info, Error **errp)
 {
@@ -1027,7 +1021,7 @@ int nbd_receive_negotiate(AioContext *aio_context, QIOChannel *ioc,
     assert(info->name && strlen(info->name) <= NBD_MAX_STRING_SIZE);
     trace_nbd_receive_negotiate_name(info->name);
 
-    result = nbd_start_negotiate(aio_context, ioc, tlscreds, hostname, outioc,
+    result = nbd_start_negotiate(ioc, tlscreds, hostname, outioc,
                                  info->structured_reply, &zeroes, errp);
     if (result < 0) {
         return result;
@@ -1150,7 +1144,7 @@ int nbd_receive_export_list(QIOChannel *ioc, QCryptoTLSCreds *tlscreds,
     QIOChannel *sioc = NULL;
 
     *info = NULL;
-    result = nbd_start_negotiate(NULL, ioc, tlscreds, hostname, &sioc, true,
+    result = nbd_start_negotiate(ioc, tlscreds, hostname, &sioc, true,
                                  NULL, errp);
     if (tlscreds && sioc) {
         ioc = sioc;

nbd/server.c

@@ -1333,6 +1333,7 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
      */
 
     qio_channel_set_blocking(client->ioc, false, NULL);
+    qio_channel_set_follow_coroutine_ctx(client->ioc, true);
 
     trace_nbd_negotiate_begin();
     memcpy(buf, "NBDMAGIC", 8);
@@ -1352,11 +1353,6 @@ static coroutine_fn int nbd_negotiate(NBDClient *client, Error **errp)
         return ret;
     }
 
-    /* Attach the channel to the same AioContext as the export */
-    if (client->exp && client->exp->common.ctx) {
-        qio_channel_attach_aio_context(client->ioc, client->exp->common.ctx);
-    }
-
     assert(!client->optlen);
     trace_nbd_negotiate_success();
 
@@ -1465,7 +1461,6 @@ void nbd_client_put(NBDClient *client)
          */
         assert(client->closing);
 
-        qio_channel_detach_aio_context(client->ioc);
         object_unref(OBJECT(client->sioc));
         object_unref(OBJECT(client->ioc));
         if (client->tlscreds) {
@@ -1544,8 +1539,6 @@ static void blk_aio_attached(AioContext *ctx, void *opaque)
     exp->common.ctx = ctx;
 
     QTAILQ_FOREACH(client, &exp->clients, next) {
-        qio_channel_attach_aio_context(client->ioc, ctx);
-
         assert(client->nb_requests == 0);
         assert(client->recv_coroutine == NULL);
         assert(client->send_coroutine == NULL);
@@ -1555,14 +1548,9 @@ static void blk_aio_attached(AioContext *ctx, void *opaque)
 static void blk_aio_detach(void *opaque)
 {
     NBDExport *exp = opaque;
-    NBDClient *client;
 
     trace_nbd_blk_aio_detach(exp->name, exp->common.ctx);
 
-    QTAILQ_FOREACH(client, &exp->clients, next) {
-        qio_channel_detach_aio_context(client->ioc);
-    }
-
     exp->common.ctx = NULL;
 }
 

qemu-nbd.c

@@ -73,8 +73,6 @@
 
 #define MBR_SIZE 512
 
-static char *srcpath;
-static SocketAddress *saddr;
 static int persistent = 0;
 static enum { RUNNING, TERMINATE, TERMINATED } state;
 static int shared = 1;
@@ -253,6 +251,29 @@ static int qemu_nbd_client_list(SocketAddress *saddr, QCryptoTLSCreds *tls,
 }
 
 
+struct NbdClientOpts {
+    char *device;
+    char *srcpath;
+    SocketAddress *saddr;
+    int old_stderr;
+    bool fork_process;
+    bool verbose;
+};
+
+static void nbd_client_release_pipe(int old_stderr)
+{
+    /* Close stderr so that the qemu-nbd process exits.  */
+    if (dup2(old_stderr, STDERR_FILENO) < 0) {
+        error_report("Could not release pipe to parent: %s",
+                     strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+    if (old_stderr != STDOUT_FILENO && close(old_stderr) < 0) {
+        error_report("Could not release qemu-nbd: %s", strerror(errno));
+        exit(EXIT_FAILURE);
+    }
+}
+
 #if HAVE_NBD_DEVICE
 static void *show_parts(void *arg)
 {
@@ -271,12 +292,6 @@ static void *show_parts(void *arg)
     return NULL;
 }
 
-struct NbdClientOpts {
-    char *device;
-    bool fork_process;
-    bool verbose;
-};
-
 static void *nbd_client_thread(void *arg)
 {
     struct NbdClientOpts *opts = arg;
@@ -289,14 +304,14 @@ static void *nbd_client_thread(void *arg)
 
     sioc = qio_channel_socket_new();
     if (qio_channel_socket_connect_sync(sioc,
-                                        saddr,
+                                        opts->saddr,
                                         &local_error) < 0) {
         error_report_err(local_error);
         goto out;
     }
 
-    if (nbd_receive_negotiate(NULL, QIO_CHANNEL(sioc),
+    if (nbd_receive_negotiate(QIO_CHANNEL(sioc), NULL, NULL, NULL,
-                              NULL, NULL, NULL, &info, &local_error) < 0) {
+                              &info, &local_error) < 0) {
         if (local_error) {
             error_report_err(local_error);
         }
@@ -320,14 +335,9 @@ static void *nbd_client_thread(void *arg)
 
     if (opts->verbose && !opts->fork_process) {
         fprintf(stderr, "NBD device %s is now connected to %s\n",
-                opts->device, srcpath);
+                opts->device, opts->srcpath);
     } else {
-        /* Close stderr so that the qemu-nbd process exits.  */
+        nbd_client_release_pipe(opts->old_stderr);
-        if (dup2(STDOUT_FILENO, STDERR_FILENO) < 0) {
-            error_report("Could not set stderr to /dev/null: %s",
-                         strerror(errno));
-            exit(EXIT_FAILURE);
-        }
     }
 
     if (nbd_client(fd) < 0) {
@@ -519,7 +529,6 @@ int main(int argc, char **argv)
     const char *bindto = NULL;
     const char *port = NULL;
     char *sockpath = NULL;
-    char *device = NULL;
     QemuOpts *sn_opts = NULL;
     const char *sn_id_or_name = NULL;
     const char *sopt = "hVb:o:p:rsnc:dvk:e:f:tl:x:T:D:AB:L";
@@ -582,16 +591,19 @@ int main(int argc, char **argv)
     const char *tlshostname = NULL;
     bool imageOpts = false;
     bool writethrough = false; /* Client will flush as needed. */
-    bool verbose = false;
-    bool fork_process = false;
     bool list = false;
     unsigned socket_activation;
     const char *pid_file_name = NULL;
     const char *selinux_label = NULL;
     BlockExportOptions *export_opts;
-#if HAVE_NBD_DEVICE
+    struct NbdClientOpts opts = {
-    struct NbdClientOpts opts;
+        .fork_process = false,
-#endif
+        .verbose = false,
+        .device = NULL,
+        .srcpath = NULL,
+        .saddr = NULL,
+        .old_stderr = STDOUT_FILENO,
+    };
 
 #ifdef CONFIG_POSIX
     os_setup_early_signal_handling();
@@ -719,7 +731,7 @@ int main(int argc, char **argv)
             disconnect = true;
             break;
         case 'c':
-            device = optarg;
+            opts.device = optarg;
             break;
         case 'e':
             if (qemu_strtoi(optarg, NULL, 0, &shared) < 0 ||
@@ -750,7 +762,7 @@ int main(int argc, char **argv)
             }
             break;
         case 'v':
-            verbose = true;
+            opts.verbose = true;
             break;
         case 'V':
             version(argv[0]);
@@ -782,7 +794,7 @@ int main(int argc, char **argv)
             tlsauthz = optarg;
             break;
         case QEMU_NBD_OPT_FORK:
-            fork_process = true;
+            opts.fork_process = true;
             break;
         case 'L':
             list = true;
@@ -802,12 +814,12 @@ int main(int argc, char **argv)
             exit(EXIT_FAILURE);
         }
         if (export_name || export_description || dev_offset ||
-            device || disconnect || fmt || sn_id_or_name || bitmaps ||
+            opts.device || disconnect || fmt || sn_id_or_name || bitmaps ||
             alloc_depth || seen_aio || seen_discard || seen_cache) {
             error_report("List mode is incompatible with per-device settings");
             exit(EXIT_FAILURE);
         }
-        if (fork_process) {
+        if (opts.fork_process) {
             error_report("List mode is incompatible with forking");
             exit(EXIT_FAILURE);
         }
@@ -832,7 +844,8 @@ int main(int argc, char **argv)
         }
     } else {
         /* Using socket activation - check user didn't use -p etc. */
-        const char *err_msg = socket_activation_validate_opts(device, sockpath,
+        const char *err_msg = socket_activation_validate_opts(opts.device,
+                                                              sockpath,
                                                               bindto, port,
                                                               selinux_label,
                                                               list);
@@ -850,7 +863,7 @@ int main(int argc, char **argv)
     }
 
     if (tlscredsid) {
-        if (device) {
+        if (opts.device) {
             error_report("TLS is not supported with a host device");
             exit(EXIT_FAILURE);
         }
@@ -880,7 +893,7 @@ int main(int argc, char **argv)
 
     if (selinux_label) {
 #ifdef CONFIG_SELINUX
-        if (sockpath == NULL && device == NULL) {
+        if (sockpath == NULL && opts.device == NULL) {
             error_report("--selinux-label is not permitted without --socket");
             exit(EXIT_FAILURE);
         }
@@ -891,13 +904,13 @@ int main(int argc, char **argv)
     }
 
     if (list) {
-        saddr = nbd_build_socket_address(sockpath, bindto, port);
+        opts.saddr = nbd_build_socket_address(sockpath, bindto, port);
-        return qemu_nbd_client_list(saddr, tlscreds,
+        return qemu_nbd_client_list(opts.saddr, tlscreds,
                                     tlshostname ? tlshostname : bindto);
     }
 
 #if !HAVE_NBD_DEVICE
-    if (disconnect || device) {
+    if (disconnect || opts.device) {
         error_report("Kernel /dev/nbdN support not available");
         exit(EXIT_FAILURE);
     }
@@ -919,7 +932,7 @@ int main(int argc, char **argv)
     }
 #endif
 
-    if ((device && !verbose) || fork_process) {
+    if ((opts.device && !opts.verbose) || opts.fork_process) {
 #ifndef WIN32
         g_autoptr(GError) err = NULL;
         int stderr_fd[2];
@@ -944,6 +957,16 @@ int main(int argc, char **argv)
 
             close(stderr_fd[0]);
 
+            /* Remember parent's stderr if we will be restoring it. */
+            if (opts.verbose /* fork_process is set */) {
+                opts.old_stderr = dup(STDERR_FILENO);
+                if (opts.old_stderr < 0) {
+                    error_report("Could not dup original stderr: %s",
+                                 strerror(errno));
+                    exit(EXIT_FAILURE);
+                }
+            }
+
             ret = qemu_daemon(1, 0);
             saved_errno = errno;    /* dup2 will overwrite error below */
 
@@ -1002,9 +1025,9 @@ int main(int argc, char **argv)
 #endif /* WIN32 */
     }
 
-    if (device != NULL && sockpath == NULL) {
+    if (opts.device != NULL && sockpath == NULL) {
         sockpath = g_malloc(128);
-        snprintf(sockpath, 128, SOCKET_PATH, basename(device));
+        snprintf(sockpath, 128, SOCKET_PATH, basename(opts.device));
     }
 
     server = qio_net_listener_new();
@@ -1023,8 +1046,8 @@ int main(int argc, char **argv)
             exit(EXIT_FAILURE);
         }
 #endif
-        saddr = nbd_build_socket_address(sockpath, bindto, port);
+        opts.saddr = nbd_build_socket_address(sockpath, bindto, port);
-        if (qio_net_listener_open_sync(server, saddr, backlog,
+        if (qio_net_listener_open_sync(server, opts.saddr, backlog,
                                        &local_err) < 0) {
             object_unref(OBJECT(server));
             error_report_err(local_err);
@@ -1059,19 +1082,19 @@ int main(int argc, char **argv)
     bdrv_init();
     atexit(qemu_nbd_shutdown);
 
-    srcpath = argv[optind];
+    opts.srcpath = argv[optind];
     if (imageOpts) {
-        QemuOpts *opts;
+        QemuOpts *o;
         if (fmt) {
             error_report("--image-opts and -f are mutually exclusive");
             exit(EXIT_FAILURE);
         }
-        opts = qemu_opts_parse_noisily(&file_opts, srcpath, true);
+        o = qemu_opts_parse_noisily(&file_opts, opts.srcpath, true);
-        if (!opts) {
+        if (!o) {
             qemu_opts_reset(&file_opts);
             exit(EXIT_FAILURE);
         }
-        options = qemu_opts_to_qdict(opts, NULL);
+        options = qemu_opts_to_qdict(o, NULL);
         qemu_opts_reset(&file_opts);
         blk = blk_new_open(NULL, NULL, options, flags, &local_err);
     } else {
@@ -1079,7 +1102,7 @@ int main(int argc, char **argv)
             options = qdict_new();
             qdict_put_str(options, "driver", fmt);
         }
-        blk = blk_new_open(srcpath, NULL, options, flags, &local_err);
+        blk = blk_new_open(opts.srcpath, NULL, options, flags, &local_err);
     }
 
     if (!blk) {
@@ -1145,15 +1168,9 @@ int main(int argc, char **argv)
     blk_exp_add(export_opts, &error_fatal);
     qapi_free_BlockExportOptions(export_opts);
 
-    if (device) {
+    if (opts.device) {
 #if HAVE_NBD_DEVICE
         int ret;
-        opts = (struct NbdClientOpts) {
-            .device = device,
-            .fork_process = fork_process,
-            .verbose = verbose,
-        };
-
         ret = pthread_create(&client_thread, NULL, nbd_client_thread, &opts);
         if (ret != 0) {
             error_report("Failed to create client thread: %s", strerror(ret));
@@ -1179,12 +1196,8 @@ int main(int argc, char **argv)
         exit(EXIT_FAILURE);
     }
 
-    if (fork_process) {
+    if (opts.fork_process) {
-        if (dup2(STDOUT_FILENO, STDERR_FILENO) < 0) {
+        nbd_client_release_pipe(opts.old_stderr);
-            error_report("Could not set stderr to /dev/null: %s",
-                         strerror(errno));
-            exit(EXIT_FAILURE);
-        }
     }
 
     state = RUNNING;
@@ -1203,7 +1216,7 @@ int main(int argc, char **argv)
 
     qemu_opts_del(sn_opts);
 
-    if (device) {
+    if (opts.device) {
         void *ret;
         pthread_join(client_thread, &ret);
         exit(ret != NULL);

scsi/qemu-pr-helper.c

@@ -735,8 +735,7 @@ static void coroutine_fn prh_co_entry(void *opaque)
 
     qio_channel_set_blocking(QIO_CHANNEL(client->ioc),
                              false, NULL);
-    qio_channel_attach_aio_context(QIO_CHANNEL(client->ioc),
+    qio_channel_set_follow_coroutine_ctx(QIO_CHANNEL(client->ioc), true);
-                                   qemu_get_aio_context());
 
     /* A very simple negotiation for future extensibility.  No features
      * are defined so write 0.
@@ -796,7 +795,6 @@ static void coroutine_fn prh_co_entry(void *opaque)
     }
 
 out:
-    qio_channel_detach_aio_context(QIO_CHANNEL(client->ioc));
     object_unref(OBJECT(client->ioc));
     g_free(client);
 }

tests/qemu-iotests/197

@@ -136,18 +136,18 @@ IMGPROTO=file IMGFMT=qcow2 TEST_IMG_FILE="$TEST_WRAP" \
 $QEMU_IO -c "write -P 0xaa 0 64k" "$TEST_IMG" | _filter_qemu_io
 
 # Allocate individual subclusters in the top image, and not the whole cluster
-$QEMU_IO -c "write -P 0xbb 28K 2K" -c "write -P 0xcc 34K 2K" "$TEST_WRAP" \
+$QEMU_IO -f qcow2 -c "write -P 0xbb 28K 2K" -c "write -P 0xcc 34K 2K" "$TEST_WRAP" \
     | _filter_qemu_io
 
 # Only 2 subclusters should be allocated in the top image at this point
-$QEMU_IMG map "$TEST_WRAP" | _filter_qemu_img_map
+$QEMU_IO -f qcow2 -c map "$TEST_WRAP"
 
 # Actual copy-on-read operation
-$QEMU_IO -C -c "read -P 0xaa 30K 4K" "$TEST_WRAP" | _filter_qemu_io
+$QEMU_IO -f qcow2 -C -c "read -P 0xaa 30K 4K" "$TEST_WRAP" | _filter_qemu_io
 
 # And here we should have 4 subclusters allocated right in the middle of the
 # top image. Make sure the whole cluster remains unallocated
-$QEMU_IMG map "$TEST_WRAP" | _filter_qemu_img_map
+$QEMU_IO -f qcow2 -c map "$TEST_WRAP"
 
 _check_test_img
 

tests/qemu-iotests/197.out

@@ -42,17 +42,15 @@ wrote 2048/2048 bytes at offset 28672
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
 wrote 2048/2048 bytes at offset 34816
 2 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Offset          Length          File
+28 KiB (0x7000) bytes not allocated at offset 0 bytes (0x0)
-0               0x7000          TEST_DIR/t.IMGFMT
+2 KiB (0x800) bytes     allocated at offset 28 KiB (0x7000)
-0x7000          0x800           TEST_DIR/t.wrap.IMGFMT
+4 KiB (0x1000) bytes not allocated at offset 30 KiB (0x7800)
-0x7800          0x1000          TEST_DIR/t.IMGFMT
+2 KiB (0x800) bytes     allocated at offset 34 KiB (0x8800)
-0x8800          0x800           TEST_DIR/t.wrap.IMGFMT
+28 KiB (0x7000) bytes not allocated at offset 36 KiB (0x9000)
-0x9000          0x7000          TEST_DIR/t.IMGFMT
 read 4096/4096 bytes at offset 30720
 4 KiB, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec)
-Offset          Length          File
+28 KiB (0x7000) bytes not allocated at offset 0 bytes (0x0)
-0               0x7000          TEST_DIR/t.IMGFMT
+8 KiB (0x2000) bytes     allocated at offset 28 KiB (0x7000)
-0x7000          0x2000          TEST_DIR/t.wrap.IMGFMT
+28 KiB (0x7000) bytes not allocated at offset 36 KiB (0x9000)
-0x9000          0x7000          TEST_DIR/t.IMGFMT
 No errors were found on the image.
 *** done

util/iov.c

@@ -571,7 +571,7 @@ static int sortelem_cmp_src_index(const void *a, const void *b)
  */
 void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf)
 {
-    IOVectorSortElem sortelems[src->niov];
+    g_autofree IOVectorSortElem *sortelems = g_new(IOVectorSortElem, src->niov);
     void *last_end;
     int i;
 

util/vhost-user-server.c

@@ -127,7 +127,14 @@ vu_message_read(VuDev *vu_dev, int conn_fd, VhostUserMsg *vmsg)
         if (rc < 0) {
             if (rc == QIO_CHANNEL_ERR_BLOCK) {
                 assert(local_err == NULL);
+                if (server->ctx) {
+                    server->in_qio_channel_yield = true;
                     qio_channel_yield(ioc, G_IO_IN);
+                    server->in_qio_channel_yield = false;
+                } else {
+                    /* Wait until attached to an AioContext again */
+                    qemu_coroutine_yield();
+                }
                 continue;
             } else {
                 error_report_err(local_err);
@@ -278,7 +285,7 @@ set_watch(VuDev *vu_dev, int fd, int vu_evt,
         vu_fd_watch->fd = fd;
         vu_fd_watch->cb = cb;
         qemu_socket_set_nonblock(fd);
-        aio_set_fd_handler(server->ioc->ctx, fd, kick_handler,
+        aio_set_fd_handler(server->ctx, fd, kick_handler,
                            NULL, NULL, NULL, vu_fd_watch);
         vu_fd_watch->vu_dev = vu_dev;
         vu_fd_watch->pvt = pvt;
@@ -299,7 +306,7 @@ static void remove_watch(VuDev *vu_dev, int fd)
     if (!vu_fd_watch) {
         return;
     }
-    aio_set_fd_handler(server->ioc->ctx, fd, NULL, NULL, NULL, NULL, NULL);
+    aio_set_fd_handler(server->ctx, fd, NULL, NULL, NULL, NULL, NULL);
 
     QTAILQ_REMOVE(&server->vu_fd_watches, vu_fd_watch, next);
     g_free(vu_fd_watch);
@@ -344,6 +351,8 @@ static void vu_accept(QIONetListener *listener, QIOChannelSocket *sioc,
     /* TODO vu_message_write() spins if non-blocking! */
     qio_channel_set_blocking(server->ioc, false, NULL);
 
+    qio_channel_set_follow_coroutine_ctx(server->ioc, true);
+
     server->co_trip = qemu_coroutine_create(vu_client_trip, server);
 
     aio_context_acquire(server->ctx);
@@ -399,13 +408,12 @@ void vhost_user_server_attach_aio_context(VuServer *server, AioContext *ctx)
         return;
     }
 
-    qio_channel_attach_aio_context(server->ioc, ctx);
-
     QTAILQ_FOREACH(vu_fd_watch, &server->vu_fd_watches, next) {
         aio_set_fd_handler(ctx, vu_fd_watch->fd, kick_handler, NULL,
                            NULL, NULL, vu_fd_watch);
     }
 
+    assert(!server->in_qio_channel_yield);
     aio_co_schedule(ctx, server->co_trip);
 }
 
@@ -419,11 +427,16 @@ void vhost_user_server_detach_aio_context(VuServer *server)
             aio_set_fd_handler(server->ctx, vu_fd_watch->fd,
                                NULL, NULL, NULL, NULL, vu_fd_watch);
         }
-
-        qio_channel_detach_aio_context(server->ioc);
     }
 
     server->ctx = NULL;
+
+    if (server->ioc) {
+        if (server->in_qio_channel_yield) {
+            /* Stop receiving the next vhost-user message */
+            qio_channel_wake_read(server->ioc);
+        }
+    }
 }
 
 bool vhost_user_server_start(VuServer *server,