Merge remote-tracking branch 'remotes/marcandre/tags/for-6.0-pull-request' into staging

For 6.0 misc patches under my radar.

V2:
 - "tests: Add tests for yank with the chardev-change case" updated
 - drop the readthedoc theme patch

# gpg: Signature made Thu 01 Apr 2021 12:54:52 BST
# gpg:                using RSA key 87A9BD933F87C606D276F62DDAE8E10975969CE5
# gpg:                issuer "marcandre.lureau@redhat.com"
# gpg: Good signature from "Marc-André Lureau <marcandre.lureau@redhat.com>" [full]
# gpg:                 aka "Marc-André Lureau <marcandre.lureau@gmail.com>" [full]
# Primary key fingerprint: 87A9 BD93 3F87 C606 D276  F62D DAE8 E109 7596 9CE5

* remotes/marcandre/tags/for-6.0-pull-request:
  tests: Add tests for yank with the chardev-change case
  chardev: Fix yank with the chardev-change case
  chardev/char.c: Always pass id to chardev_new
  chardev/char.c: Move object_property_try_add_child out of chardev_new
  yank: Always link full yank code
  yank: Remove dependency on qiochannel
  docs: simplify each section title
  dbus-vmstate: Increase the size of input stream buffer used during load
  util: fix use-after-free in module_load_one

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

25 files changed, 417 insertions, 106 deletions

diff --git a/MAINTAINERS b/MAINTAINERS
index 554be84b32..aa894767dc 100644
--- a/MAINTAINERS
+++ b/MAINTAINERS
@@ -2822,7 +2822,8 @@ Yank feature
 M: Lukas Straub <lukasstraub2@web.de>
 S: Odd fixes
 F: util/yank.c
-F: stubs/yank.c
+F: migration/yank_functions*
+F: tests/unit/test-yank.c
 F: include/qemu/yank.h
 F: qapi/yank.json
 
diff --git a/backends/dbus-vmstate.c b/backends/dbus-vmstate.c
index 2a0d2e4a31..9cfd758c42 100644
--- a/backends/dbus-vmstate.c
+++ b/backends/dbus-vmstate.c
@@ -204,6 +204,8 @@ static int dbus_vmstate_post_load(void *opaque, int version_id)
     m = g_memory_input_stream_new_from_data(self->data, self->data_size, NULL);
     s = g_data_input_stream_new(m);
     g_data_input_stream_set_byte_order(s, G_DATA_STREAM_BYTE_ORDER_BIG_ENDIAN);
+    g_buffered_input_stream_set_buffer_size(G_BUFFERED_INPUT_STREAM(s),
+                                            DBUS_VMSTATE_SIZE_LIMIT);
 
     nelem = g_data_input_stream_read_uint32(s, NULL, &err);
     if (err) {
@@ -244,11 +246,23 @@ static int dbus_vmstate_post_load(void *opaque, int version_id)
         }
 
         len = g_data_input_stream_read_uint32(s, NULL, &err);
+        if (len > DBUS_VMSTATE_SIZE_LIMIT) {
+            error_report("%s: Invalid vmstate size: %u", __func__, len);
+            return -1;
+        }
+
+        g_buffered_input_stream_fill(G_BUFFERED_INPUT_STREAM(s), len, NULL,
+                                     &err);
+        if (err) {
+            goto error;
+        }
+
         avail = g_buffered_input_stream_get_available(
             G_BUFFERED_INPUT_STREAM(s));
-
-        if (len > DBUS_VMSTATE_SIZE_LIMIT || len > avail) {
-            error_report("%s: Invalid vmstate size: %u", __func__, len);
+        if (len > avail) {
+            error_report("%s: Not enough data available to load for Id: '%s'. "
+                "Available data size: %zu, Actual vmstate size: %u",
+                __func__, id, avail, len);
             return -1;
         }
 
diff --git a/chardev/char-socket.c b/chardev/char-socket.c
index f618bdec28..daa89fe5d1 100644
--- a/chardev/char-socket.c
+++ b/chardev/char-socket.c
@@ -402,6 +402,13 @@ static void remove_hup_source(SocketChardev *s)
     }
 }
 
+static void char_socket_yank_iochannel(void *opaque)
+{
+    QIOChannel *ioc = QIO_CHANNEL(opaque);
+
+    qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+}
+
 static void tcp_chr_free_connection(Chardev *chr)
 {
     SocketChardev *s = SOCKET_CHARDEV(chr);
@@ -424,7 +431,7 @@ static void tcp_chr_free_connection(Chardev *chr)
         (s->state == TCP_CHARDEV_STATE_CONNECTING
         || s->state == TCP_CHARDEV_STATE_CONNECTED)) {
         yank_unregister_function(CHARDEV_YANK_INSTANCE(chr->label),
-                                 yank_generic_iochannel,
+                                 char_socket_yank_iochannel,
                                  QIO_CHANNEL(s->sioc));
     }
     object_unref(OBJECT(s->sioc));
@@ -946,7 +953,7 @@ static int tcp_chr_add_client(Chardev *chr, int fd)
     tcp_chr_set_client_ioc_name(chr, sioc);
     if (s->registered_yank) {
         yank_register_function(CHARDEV_YANK_INSTANCE(chr->label),
-                               yank_generic_iochannel,
+                               char_socket_yank_iochannel,
                                QIO_CHANNEL(sioc));
     }
     ret = tcp_chr_new_client(chr, sioc);
@@ -965,7 +972,7 @@ static void tcp_chr_accept(QIONetListener *listener,
     tcp_chr_set_client_ioc_name(chr, cioc);
     if (s->registered_yank) {
         yank_register_function(CHARDEV_YANK_INSTANCE(chr->label),
-                               yank_generic_iochannel,
+                               char_socket_yank_iochannel,
                                QIO_CHANNEL(cioc));
     }
     tcp_chr_new_client(chr, cioc);
@@ -985,7 +992,7 @@ static int tcp_chr_connect_client_sync(Chardev *chr, Error **errp)
     }
     if (s->registered_yank) {
         yank_register_function(CHARDEV_YANK_INSTANCE(chr->label),
-                               yank_generic_iochannel,
+                               char_socket_yank_iochannel,
                                QIO_CHANNEL(sioc));
     }
     tcp_chr_new_client(chr, sioc);
@@ -1005,7 +1012,7 @@ static void tcp_chr_accept_server_sync(Chardev *chr)
     tcp_chr_set_client_ioc_name(chr, sioc);
     if (s->registered_yank) {
         yank_register_function(CHARDEV_YANK_INSTANCE(chr->label),
-                               yank_generic_iochannel,
+                               char_socket_yank_iochannel,
                                QIO_CHANNEL(sioc));
     }
     tcp_chr_new_client(chr, sioc);
@@ -1119,7 +1126,13 @@ static void char_socket_finalize(Object *obj)
     }
     g_free(s->tls_authz);
     if (s->registered_yank) {
-        yank_unregister_instance(CHARDEV_YANK_INSTANCE(chr->label));
+        /*
+         * In the chardev-change special-case, we shouldn't unregister the yank
+         * instance, as it still may be needed.
+         */
+        if (!chr->handover_yank_instance) {
+            yank_unregister_instance(CHARDEV_YANK_INSTANCE(chr->label));
+        }
     }
 
     qemu_chr_be_event(chr, CHR_EVENT_CLOSED);
@@ -1138,7 +1151,7 @@ static void qemu_chr_socket_connected(QIOTask *task, void *opaque)
         tcp_chr_change_state(s, TCP_CHARDEV_STATE_DISCONNECTED);
         if (s->registered_yank) {
             yank_unregister_function(CHARDEV_YANK_INSTANCE(chr->label),
-                                     yank_generic_iochannel,
+                                     char_socket_yank_iochannel,
                                      QIO_CHANNEL(sioc));
         }
         check_report_connect_error(chr, err);
@@ -1176,7 +1189,7 @@ static void tcp_chr_connect_client_async(Chardev *chr)
     tcp_chr_set_client_ioc_name(chr, sioc);
     if (s->registered_yank) {
         yank_register_function(CHARDEV_YANK_INSTANCE(chr->label),
-                               yank_generic_iochannel,
+                               char_socket_yank_iochannel,
                                QIO_CHANNEL(sioc));
     }
     /*
@@ -1417,8 +1430,14 @@ static void qmp_chardev_open_socket(Chardev *chr,
         qemu_chr_set_feature(chr, QEMU_CHAR_FEATURE_FD_PASS);
     }
 
-    if (!yank_register_instance(CHARDEV_YANK_INSTANCE(chr->label), errp)) {
-        return;
+    /*
+     * In the chardev-change special-case, we shouldn't register a new yank
+     * instance, as there already may be one.
+     */
+    if (!chr->handover_yank_instance) {
+        if (!yank_register_instance(CHARDEV_YANK_INSTANCE(chr->label), errp)) {
+            return;
+        }
     }
     s->registered_yank = true;
 
@@ -1560,6 +1579,8 @@ static void char_socket_class_init(ObjectClass *oc, void *data)
 {
     ChardevClass *cc = CHARDEV_CLASS(oc);
 
+    cc->supports_yank = true;
+
     cc->parse = qemu_chr_parse_socket;
     cc->open = qmp_chardev_open_socket;
     cc->chr_wait_connected = tcp_chr_wait_connected;
diff --git a/chardev/char.c b/chardev/char.c
index 140d6d9d36..398f09df19 100644
--- a/chardev/char.c
+++ b/chardev/char.c
@@ -39,6 +39,7 @@
 #include "qemu/option.h"
 #include "qemu/id.h"
 #include "qemu/coroutine.h"
+#include "qemu/yank.h"
 
 #include "chardev-internal.h"
 
@@ -266,6 +267,7 @@ static void char_init(Object *obj)
 {
     Chardev *chr = CHARDEV(obj);
 
+    chr->handover_yank_instance = false;
     chr->logfd = -1;
     qemu_mutex_init(&chr->chr_write_lock);
 
@@ -959,6 +961,7 @@ void qemu_chr_set_feature(Chardev *chr,
 static Chardev *chardev_new(const char *id, const char *typename,
                             ChardevBackend *backend,
                             GMainContext *gcontext,
+                            bool handover_yank_instance,
                             Error **errp)
 {
     Object *obj;
@@ -967,15 +970,19 @@ static Chardev *chardev_new(const char *id, const char *typename,
     bool be_opened = true;
 
     assert(g_str_has_prefix(typename, "chardev-"));
+    assert(id);
 
     obj = object_new(typename);
     chr = CHARDEV(obj);
+    chr->handover_yank_instance = handover_yank_instance;
     chr->label = g_strdup(id);
     chr->gcontext = gcontext;
 
     qemu_char_open(chr, backend, &be_opened, &local_err);
     if (local_err) {
-        goto end;
+        error_propagate(errp, local_err);
+        object_unref(obj);
+        return NULL;
     }
 
     if (!chr->filename) {
@@ -985,22 +992,6 @@ static Chardev *chardev_new(const char *id, const char *typename,
         qemu_chr_be_event(chr, CHR_EVENT_OPENED);
     }
 
-    if (id) {
-        object_property_try_add_child(get_chardevs_root(), id, obj,
-                                      &local_err);
-        if (local_err) {
-            goto end;
-        }
-        object_unref(obj);
-    }
-
-end:
-    if (local_err) {
-        error_propagate(errp, local_err);
-        object_unref(obj);
-        return NULL;
-    }
-
     return chr;
 }
 
@@ -1009,6 +1000,7 @@ Chardev *qemu_chardev_new(const char *id, const char *typename,
                           GMainContext *gcontext,
                           Error **errp)
 {
+    Chardev *chr;
     g_autofree char *genid = NULL;
 
     if (!id) {
@@ -1016,7 +1008,19 @@ Chardev *qemu_chardev_new(const char *id, const char *typename,
         id = genid;
     }
 
-    return chardev_new(id, typename, backend, gcontext, errp);
+    chr = chardev_new(id, typename, backend, gcontext, false, errp);
+    if (!chr) {
+        return NULL;
+    }
+
+    if (!object_property_try_add_child(get_chardevs_root(), id, OBJECT(chr),
+                                       errp)) {
+        object_unref(OBJECT(chr));
+        return NULL;
+    }
+    object_unref(OBJECT(chr));
+
+    return chr;
 }
 
 ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
@@ -1032,11 +1036,18 @@ ChardevReturn *qmp_chardev_add(const char *id, ChardevBackend *backend,
     }
 
     chr = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc)),
-                      backend, NULL, errp);
+                      backend, NULL, false, errp);
     if (!chr) {
         return NULL;
     }
 
+    if (!object_property_try_add_child(get_chardevs_root(), id, OBJECT(chr),
+                                       errp)) {
+        object_unref(OBJECT(chr));
+        return NULL;
+    }
+    object_unref(OBJECT(chr));
+
     ret = g_new0(ChardevReturn, 1);
     if (CHARDEV_IS_PTY(chr)) {
         ret->pty = g_strdup(chr->filename + 4);
@@ -1050,9 +1061,10 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
                                   Error **errp)
 {
     CharBackend *be;
-    const ChardevClass *cc;
+    const ChardevClass *cc, *cc_new;
     Chardev *chr, *chr_new;
     bool closed_sent = false;
+    bool handover_yank_instance;
     ChardevReturn *ret;
 
     chr = qemu_chr_find(id);
@@ -1084,17 +1096,23 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
         return NULL;
     }
 
-    cc = char_get_class(ChardevBackendKind_str(backend->type), errp);
-    if (!cc) {
+    cc = CHARDEV_GET_CLASS(chr);
+    cc_new = char_get_class(ChardevBackendKind_str(backend->type), errp);
+    if (!cc_new) {
         return NULL;
     }
 
-    chr_new = chardev_new(NULL, object_class_get_name(OBJECT_CLASS(cc)),
-                          backend, chr->gcontext, errp);
+    /*
+     * The new chardev should not register a yank instance if the current
+     * chardev has registered one already.
+     */
+    handover_yank_instance = cc->supports_yank && cc_new->supports_yank;
+
+    chr_new = chardev_new(id, object_class_get_name(OBJECT_CLASS(cc_new)),
+                          backend, chr->gcontext, handover_yank_instance, errp);
     if (!chr_new) {
         return NULL;
     }
-    chr_new->label = g_strdup(id);
 
     if (chr->be_open && !chr_new->be_open) {
         qemu_chr_be_event(chr, CHR_EVENT_CLOSED);
@@ -1115,6 +1133,15 @@ ChardevReturn *qmp_chardev_change(const char *id, ChardevBackend *backend,
         return NULL;
     }
 
+    /* change successfull, clean up */
+    chr_new->handover_yank_instance = false;
+
+    /*
+     * When the old chardev is freed, it should not unregister the yank
+     * instance if the new chardev needs it.
+     */
+    chr->handover_yank_instance = handover_yank_instance;
+
     object_unparent(OBJECT(chr));
     object_property_add_child(get_chardevs_root(), chr_new->label,
                               OBJECT(chr_new));
diff --git a/docs/devel/index.rst b/docs/devel/index.rst
index 416261505f..6cf7e2d233 100644
--- a/docs/devel/index.rst
+++ b/docs/devel/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'devel' manual.
 
 
-QEMU Developer's Guide
-======================
+Developer Information
+=====================
 
 This manual documents various parts of the internals of QEMU.
 You only need to read it if you are interested in reading or
diff --git a/docs/interop/index.rst b/docs/interop/index.rst
index 95d56495f6..219a5e5fc5 100644
--- a/docs/interop/index.rst
+++ b/docs/interop/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'interop' manual.
 
 
-QEMU System Emulation Management and Interoperability Guide
-===========================================================
+System Emulation Management and Interoperability
+================================================
 
 This manual contains documents and specifications that are useful
 for making QEMU interoperate with other software.
diff --git a/docs/specs/index.rst b/docs/specs/index.rst
index 1b0eb979d5..7b08314d33 100644
--- a/docs/specs/index.rst
+++ b/docs/specs/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'specs' manual
 
 
-QEMU System Emulation Guest Hardware Specifications
-===================================================
+System Emulation Guest Hardware Specifications
+==============================================
 
 
 Contents:
diff --git a/docs/system/index.rst b/docs/system/index.rst
index 6ad9c93806..02d0707181 100644
--- a/docs/system/index.rst
+++ b/docs/system/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'system' manual.
 
 
-QEMU System Emulation User's Guide
-==================================
+System Emulation
+================
 
 This manual is the overall guide for users using QEMU
 for full system emulation (as opposed to user-mode emulation).
diff --git a/docs/tools/index.rst b/docs/tools/index.rst
index 3a5829c17a..d923834a73 100644
--- a/docs/tools/index.rst
+++ b/docs/tools/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'tools' manual
 
 
-QEMU Tools Guide
-================
+Tools
+=====
 
 
 Contents:
diff --git a/docs/user/index.rst b/docs/user/index.rst
index e030dadf65..a5b47459ec 100644
--- a/docs/user/index.rst
+++ b/docs/user/index.rst
@@ -1,8 +1,8 @@
 .. This is the top level page for the 'user' manual.
 
 
-QEMU User Mode Emulation User's Guide
-=====================================
+User Mode Emulation
+===================
 
 This manual is the overall guide for users using QEMU
 for user-mode emulation.  In this mode, QEMU can launch
diff --git a/include/chardev/char.h b/include/chardev/char.h
index 4181a2784a..7c0444f90d 100644
--- a/include/chardev/char.h
+++ b/include/chardev/char.h
@@ -65,6 +65,8 @@ struct Chardev {
     char *filename;
     int logfd;
     int be_open;
+    /* used to coordinate the chardev-change special-case: */
+    bool handover_yank_instance;
     GSource *gsource;
     GMainContext *gcontext;
     DECLARE_BITMAP(features, QEMU_CHAR_FEATURE_LAST);
@@ -251,6 +253,7 @@ struct ChardevClass {
     ObjectClass parent_class;
 
     bool internal; /* TODO: eventually use TYPE_USER_CREATABLE */
+    bool supports_yank;
     void (*parse)(QemuOpts *opts, ChardevBackend *backend, Error **errp);
 
     void (*open)(Chardev *chr, ChardevBackend *backend,
diff --git a/include/qemu/yank.h b/include/qemu/yank.h
index 5b93c70cbf..5375a1f195 100644
--- a/include/qemu/yank.h
+++ b/include/qemu/yank.h
@@ -73,16 +73,6 @@ void yank_unregister_function(const YankInstance *instance,
                               YankFn *func,
                               void *opaque);
 
-/**
- * yank_generic_iochannel: Generic yank function for iochannel
- *
- * This is a generic yank function which will call qio_channel_shutdown on the
- * provided QIOChannel.
- *
- * @opaque: QIOChannel to shutdown
- */
-void yank_generic_iochannel(void *opaque);
-
 #define BLOCKDEV_YANK_INSTANCE(the_node_name) (&(YankInstance) { \
         .type = YANK_INSTANCE_TYPE_BLOCK_NODE, \
         .u.block_node.node_name = (the_node_name) })
diff --git a/migration/channel.c b/migration/channel.c
index 35fe234e9c..c9ee902021 100644
--- a/migration/channel.c
+++ b/migration/channel.c
@@ -20,6 +20,7 @@
 #include "io/channel-tls.h"
 #include "io/channel-socket.h"
 #include "qemu/yank.h"
+#include "yank_functions.h"
 
 /**
  * @migration_channel_process_incoming - Create new incoming migration channel
@@ -38,7 +39,8 @@ void migration_channel_process_incoming(QIOChannel *ioc)
         ioc, object_get_typename(OBJECT(ioc)));
 
     if (object_dynamic_cast(OBJECT(ioc), TYPE_QIO_CHANNEL_SOCKET)) {
-        yank_register_function(MIGRATION_YANK_INSTANCE, yank_generic_iochannel,
+        yank_register_function(MIGRATION_YANK_INSTANCE,
+                               migration_yank_iochannel,
                                QIO_CHANNEL(ioc));
     }
 
@@ -76,7 +78,7 @@ void migration_channel_connect(MigrationState *s,
     if (!error) {
         if (object_dynamic_cast(OBJECT(ioc), TYPE_QIO_CHANNEL_SOCKET)) {
             yank_register_function(MIGRATION_YANK_INSTANCE,
-                                   yank_generic_iochannel,
+                                   migration_yank_iochannel,
                                    QIO_CHANNEL(ioc));
         }
 
diff --git a/migration/meson.build b/migration/meson.build
index 6fa2f8745d..3ecedce94d 100644
--- a/migration/meson.build
+++ b/migration/meson.build
@@ -6,6 +6,7 @@ migration_files = files(
   'vmstate.c',
   'qemu-file-channel.c',
   'qemu-file.c',
+  'yank_functions.c',
 )
 softmmu_ss.add(migration_files)
 
diff --git a/migration/multifd.c b/migration/multifd.c
index 03527c564c..a6677c45c8 100644
--- a/migration/multifd.c
+++ b/migration/multifd.c
@@ -27,6 +27,7 @@
 
 #include "qemu/yank.h"
 #include "io/channel-socket.h"
+#include "yank_functions.h"
 
 /* Multiple fd's */
 
@@ -989,7 +990,7 @@ int multifd_load_cleanup(Error **errp)
         if (object_dynamic_cast(OBJECT(p->c), TYPE_QIO_CHANNEL_SOCKET)
             && OBJECT(p->c)->ref == 1) {
             yank_unregister_function(MIGRATION_YANK_INSTANCE,
-                                     yank_generic_iochannel,
+                                     migration_yank_iochannel,
                                      QIO_CHANNEL(p->c));
         }
 
diff --git a/migration/qemu-file-channel.c b/migration/qemu-file-channel.c
index afc3a7f642..876d05a540 100644
--- a/migration/qemu-file-channel.c
+++ b/migration/qemu-file-channel.c
@@ -28,6 +28,7 @@
 #include "io/channel-socket.h"
 #include "qemu/iov.h"
 #include "qemu/yank.h"
+#include "yank_functions.h"
 
 
 static ssize_t channel_writev_buffer(void *opaque,
@@ -108,7 +109,7 @@ static int channel_close(void *opaque, Error **errp)
     if (object_dynamic_cast(OBJECT(ioc), TYPE_QIO_CHANNEL_SOCKET)
         && OBJECT(ioc)->ref == 1) {
         yank_unregister_function(MIGRATION_YANK_INSTANCE,
-                                 yank_generic_iochannel,
+                                 migration_yank_iochannel,
                                  QIO_CHANNEL(ioc));
     }
     object_unref(OBJECT(ioc));
diff --git a/migration/yank_functions.c b/migration/yank_functions.c
new file mode 100644
index 0000000000..96c90e17dc
--- /dev/null
+++ b/migration/yank_functions.c
@@ -0,0 +1,20 @@
+/*
+ * migration yank functions
+ *
+ * Copyright (c) Lukas Straub <lukasstraub2@web.de>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include "qapi/error.h"
+#include "io/channel.h"
+#include "yank_functions.h"
+
+void migration_yank_iochannel(void *opaque)
+{
+    QIOChannel *ioc = QIO_CHANNEL(opaque);
+
+    qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
+}
diff --git a/migration/yank_functions.h b/migration/yank_functions.h
new file mode 100644
index 0000000000..055ea22523
--- /dev/null
+++ b/migration/yank_functions.h
@@ -0,0 +1,17 @@
+/*
+ * migration yank functions
+ *
+ * Copyright (c) Lukas Straub <lukasstraub2@web.de>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+/**
+ * migration_yank_iochannel: yank function for iochannel
+ *
+ * This yank function will call qio_channel_shutdown on the provided QIOChannel.
+ *
+ * @opaque: QIOChannel to shutdown
+ */
+void migration_yank_iochannel(void *opaque);
diff --git a/stubs/meson.build b/stubs/meson.build
index 8a3e804cf0..be6f6d609e 100644
--- a/stubs/meson.build
+++ b/stubs/meson.build
@@ -46,7 +46,6 @@ stub_ss.add(files('vm-stop.c'))
 stub_ss.add(files('win32-kbd-hook.c'))
 stub_ss.add(files('cpu-synchronize-state.c'))
 if have_block
-  stub_ss.add(files('yank.c'))
   stub_ss.add(files('replay-tools.c'))
 endif
 if have_system
diff --git a/stubs/yank.c b/stubs/yank.c
deleted file mode 100644
index 6090416065..0000000000
--- a/stubs/yank.c
+++ /dev/null
@@ -1,29 +0,0 @@
-#include "qemu/osdep.h"
-#include "qemu/yank.h"
-
-bool yank_register_instance(const YankInstance *instance, Error **errp)
-{
-    return true;
-}
-
-void yank_unregister_instance(const YankInstance *instance)
-{
-}
-
-void yank_register_function(const YankInstance *instance,
-                            YankFn *func,
-                            void *opaque)
-{
-}
-
-void yank_unregister_function(const YankInstance *instance,
-                              YankFn *func,
-                              void *opaque)
-{
-}
-
-void yank_generic_iochannel(void *opaque)
-{
-}
-
-
diff --git a/tests/unit/meson.build b/tests/unit/meson.build
index 4bfe4627ba..b3bc2109da 100644
--- a/tests/unit/meson.build
+++ b/tests/unit/meson.build
@@ -123,7 +123,8 @@ if have_system
     'test-util-sockets': ['socket-helpers.c'],
     'test-base64': [],
     'test-bufferiszero': [],
-    'test-vmstate': [migration, io]
+    'test-vmstate': [migration, io],
+    'test-yank': ['socket-helpers.c', qom, io, chardev]
   }
   if 'CONFIG_INOTIFY1' in config_host
     tests += {'test-util-filemonitor': []}
diff --git a/tests/unit/test-yank.c b/tests/unit/test-yank.c
new file mode 100644
index 0000000000..2383d2908c
--- /dev/null
+++ b/tests/unit/test-yank.c
@@ -0,0 +1,249 @@
+/*
+ * Tests for QEMU yank feature
+ *
+ * Copyright (c) Lukas Straub <lukasstraub2@web.de>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2 or later.
+ * See the COPYING file in the top-level directory.
+ */
+
+#include "qemu/osdep.h"
+#include <glib/gstdio.h>
+
+#include "qemu/config-file.h"
+#include "qemu/module.h"
+#include "qemu/option.h"
+#include "chardev/char-fe.h"
+#include "sysemu/sysemu.h"
+#include "qapi/error.h"
+#include "qapi/qapi-commands-char.h"
+#include "qapi/qapi-types-char.h"
+#include "qapi/qapi-commands-yank.h"
+#include "qapi/qapi-types-yank.h"
+#include "io/channel-socket.h"
+#include "socket-helpers.h"
+
+typedef struct {
+    SocketAddress *addr;
+    bool old_yank;
+    bool new_yank;
+    bool fail;
+} CharChangeTestConfig;
+
+static int chardev_change(void *opaque)
+{
+    return 0;
+}
+
+static bool is_yank_instance_registered(void)
+{
+    YankInstanceList *list;
+    bool ret;
+
+    list = qmp_query_yank(&error_abort);
+
+    ret = !!list;
+
+    qapi_free_YankInstanceList(list);
+
+    return ret;
+}
+
+static gpointer accept_thread(gpointer data)
+{
+    QIOChannelSocket *ioc = data;
+    QIOChannelSocket *cioc;
+
+    cioc = qio_channel_socket_accept(ioc, &error_abort);
+    object_unref(OBJECT(cioc));
+
+    return NULL;
+}
+
+static void char_change_test(gconstpointer opaque)
+{
+    CharChangeTestConfig *conf = (gpointer) opaque;
+    SocketAddress *addr;
+    Chardev *chr;
+    CharBackend be;
+    ChardevReturn *ret;
+    QIOChannelSocket *ioc;
+    QemuThread thread;
+
+    /*
+     * Setup a listener socket and determine its address
+     * so we know the TCP port for the client later
+     */
+    ioc = qio_channel_socket_new();
+    g_assert_nonnull(ioc);
+    qio_channel_socket_listen_sync(ioc, conf->addr, 1, &error_abort);
+    addr = qio_channel_socket_get_local_address(ioc, &error_abort);
+    g_assert_nonnull(addr);
+
+    ChardevBackend backend[2] = {
+        /* doesn't support yank */
+        { .type = CHARDEV_BACKEND_KIND_NULL },
+        /* supports yank */
+        {
+            .type = CHARDEV_BACKEND_KIND_SOCKET,
+            .u.socket.data = &(ChardevSocket) {
+                .addr = &(SocketAddressLegacy) {
+                    .type = SOCKET_ADDRESS_LEGACY_KIND_INET,
+                    .u.inet.data = &addr->u.inet
+                },
+                .has_server = true,
+                .server = false
+            }
+        } };
+
+    ChardevBackend fail_backend[2] = {
+        /* doesn't support yank */
+        {
+            .type = CHARDEV_BACKEND_KIND_UDP,
+            .u.udp.data = &(ChardevUdp) {
+                .remote = &(SocketAddressLegacy) {
+                    .type = SOCKET_ADDRESS_LEGACY_KIND_UNIX,
+                    .u.q_unix.data = &(UnixSocketAddress) {
+                        .path = (char *)""
+                    }
+                }
+            }
+        },
+        /* supports yank */
+        {
+            .type = CHARDEV_BACKEND_KIND_SOCKET,
+            .u.socket.data = &(ChardevSocket) {
+                .addr = &(SocketAddressLegacy) {
+                    .type = SOCKET_ADDRESS_LEGACY_KIND_INET,
+                    .u.inet.data = &(InetSocketAddress) {
+                        .host = (char *)"127.0.0.1",
+                        .port = (char *)"0"
+                    }
+                },
+                .has_server = true,
+                .server = false
+            }
+        } };
+
+    g_assert(!is_yank_instance_registered());
+
+    if (conf->old_yank) {
+        qemu_thread_create(&thread, "accept", accept_thread,
+                           ioc, QEMU_THREAD_JOINABLE);
+    }
+
+    ret = qmp_chardev_add("chardev", &backend[conf->old_yank], &error_abort);
+    qapi_free_ChardevReturn(ret);
+    chr = qemu_chr_find("chardev");
+    g_assert_nonnull(chr);
+
+    g_assert(is_yank_instance_registered() == conf->old_yank);
+
+    qemu_chr_wait_connected(chr, &error_abort);
+    if (conf->old_yank) {
+        qemu_thread_join(&thread);
+    }
+
+    qemu_chr_fe_init(&be, chr, &error_abort);
+    /* allow chardev-change */
+    qemu_chr_fe_set_handlers(&be, NULL, NULL,
+                             NULL, chardev_change, NULL, NULL, true);
+
+    if (conf->fail) {
+        g_setenv("QTEST_SILENT_ERRORS", "1", 1);
+        ret = qmp_chardev_change("chardev", &fail_backend[conf->new_yank],
+                                 NULL);
+        g_assert_null(ret);
+        g_assert(be.chr == chr);
+        g_assert(is_yank_instance_registered() == conf->old_yank);
+        g_unsetenv("QTEST_SILENT_ERRORS");
+    } else {
+        if (conf->new_yank) {
+                qemu_thread_create(&thread, "accept", accept_thread,
+                                   ioc, QEMU_THREAD_JOINABLE);
+        }
+        ret = qmp_chardev_change("chardev", &backend[conf->new_yank],
+                                 &error_abort);
+        if (conf->new_yank) {
+            qemu_thread_join(&thread);
+        }
+        g_assert_nonnull(ret);
+        g_assert(be.chr != chr);
+        g_assert(is_yank_instance_registered() == conf->new_yank);
+    }
+
+    object_unparent(OBJECT(be.chr));
+    object_unref(OBJECT(ioc));
+    qapi_free_ChardevReturn(ret);
+    qapi_free_SocketAddress(addr);
+}
+
+static SocketAddress tcpaddr = {
+    .type = SOCKET_ADDRESS_TYPE_INET,
+    .u.inet.host = (char *)"127.0.0.1",
+    .u.inet.port = (char *)"0",
+};
+
+int main(int argc, char **argv)
+{
+    bool has_ipv4, has_ipv6;
+
+    qemu_init_main_loop(&error_abort);
+    socket_init();
+
+    g_test_init(&argc, &argv, NULL);
+
+    if (socket_check_protocol_support(&has_ipv4, &has_ipv6) < 0) {
+        g_printerr("socket_check_protocol_support() failed\n");
+        goto end;
+    }
+
+    if (!has_ipv4) {
+        goto end;
+    }
+
+    module_call_init(MODULE_INIT_QOM);
+    qemu_add_opts(&qemu_chardev_opts);
+
+    g_test_add_data_func("/yank/char_change/success/to_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = false,
+                                                   .new_yank = true,
+                                                   .fail = false },
+                         char_change_test);
+    g_test_add_data_func("/yank/char_change/fail/to_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = false,
+                                                   .new_yank = true,
+                                                   .fail = true },
+                         char_change_test);
+
+    g_test_add_data_func("/yank/char_change/success/yank_to_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = true,
+                                                   .new_yank = true,
+                                                   .fail = false },
+                         char_change_test);
+    g_test_add_data_func("/yank/char_change/fail/yank_to_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = true,
+                                                   .new_yank = true,
+                                                   .fail = true },
+                         char_change_test);
+
+    g_test_add_data_func("/yank/char_change/success/from_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = true,
+                                                   .new_yank = false,
+                                                   .fail = false },
+                         char_change_test);
+    g_test_add_data_func("/yank/char_change/fail/from_yank",
+                         &(CharChangeTestConfig) { .addr = &tcpaddr,
+                                                   .old_yank = true,
+                                                   .new_yank = false,
+                                                   .fail = true },
+                         char_change_test);
+
+end:
+    return g_test_run();
+}
diff --git a/util/meson.build b/util/meson.build
index 984fba965f..510765cde4 100644
--- a/util/meson.build
+++ b/util/meson.build
@@ -43,6 +43,7 @@ util_ss.add(files('stats64.c'))
 util_ss.add(files('systemd.c'))
 util_ss.add(when: 'CONFIG_POSIX', if_true: files('drm.c'))
 util_ss.add(files('guest-random.c'))
+util_ss.add(files('yank.c'))
 
 if have_user
   util_ss.add(files('selfmap.c'))
@@ -51,7 +52,6 @@ endif
 if have_system
   util_ss.add(files('crc-ccitt.c'))
   util_ss.add(when: 'CONFIG_GIO', if_true: [files('dbus.c'), gio])
-  util_ss.add(files('yank.c'))
   util_ss.add(when: 'CONFIG_LINUX', if_true: files('userfaultfd.c'))
 endif
 
diff --git a/util/module.c b/util/module.c
index cbe89fede6..7661d0f623 100644
--- a/util/module.c
+++ b/util/module.c
@@ -230,10 +230,11 @@ bool module_load_one(const char *prefix, const char *lib_name, bool mayfail)
         }
     }
 
-    if (!g_hash_table_add(loaded_modules, module_name)) {
+    if (g_hash_table_contains(loaded_modules, module_name)) {
         g_free(module_name);
         return true;
     }
+    g_hash_table_add(loaded_modules, module_name);
 
     search_dir = getenv("QEMU_MODULE_DIR");
     if (search_dir != NULL) {
diff --git a/util/yank.c b/util/yank.c
index fc08f65209..abf47c346d 100644
--- a/util/yank.c
+++ b/util/yank.c
@@ -15,7 +15,6 @@
 #include "qapi/qapi-commands-yank.h"
 #include "qapi/qapi-visit-yank.h"
 #include "qapi/clone-visitor.h"
-#include "io/channel.h"
 #include "qemu/yank.h"
 
 struct YankFuncAndParam {
@@ -151,13 +150,6 @@ void yank_unregister_function(const YankInstance *instance,
     abort();
 }
 
-void yank_generic_iochannel(void *opaque)
-{
-    QIOChannel *ioc = QIO_CHANNEL(opaque);
-
-    qio_channel_shutdown(ioc, QIO_CHANNEL_SHUTDOWN_BOTH, NULL);
-}
-
 void qmp_yank(YankInstanceList *instances,
               Error **errp)
 {