[RFC 0/3] Support live migration for qemu-vdagent chardev

[RFC 0/3] Support live migration for qemu-vdagent chardev

[yong.huang]

From: Hyman Huang <yong.huang@smartx.com>

Our goal is to migrate VMs that are configured with qemu-vdagent-typed
chardev while allowing the agent to continue working without having
to restart the service in guest.

Let's justify which fields should be taken into account for struct
VDAgentChardev.

struct VDAgentChardev {
    Chardev parent;

    /* config */
    bool mouse;
    bool clipboard;

    /* guest vdagent */
    uint32_t caps;
    VDIChunkHeader chunk;
    uint32_t chunksize;
    uint8_t *msgbuf;
    uint32_t msgsize;
    uint8_t *xbuf;
    uint32_t xoff, xsize;
    Buffer outbuf;

    /* mouse */
    DeviceState mouse_dev;
    uint32_t mouse_x;
    uint32_t mouse_y;
    uint32_t mouse_btn;
    uint32_t mouse_display;
    QemuInputHandlerState *mouse_hs;

    /* clipboard */
    QemuClipboardPeer cbpeer;
    uint32_t last_serial[QEMU_CLIPBOARD_SELECTION__COUNT];
    uint32_t cbpending[QEMU_CLIPBOARD_SELECTION__COUNT];
};

parent:
No dynamic information is generated. skip migrating.

mouse, clipboard:
The mouse and clipboard should be set up identically on both sides.
Skip migrating.

caps:
Store the negotiated caps between the client and the guest.
Should migrate.

chunk, ... outbuf:
The spice agent protocol's message transportation between the client
and the guest is implemented using all of these fields, however the
message loss can be tolerated by guests because the issue may occur
in the real world as well.
Could skip migrating.

mouse_dev, ... mouse_hs:
The mouse state can be reset after a live migration since the agent
working inside the guest does not heavily depend on them.
Could skip migrating

cbpeer:
Since the cbpeer would lose the data it references to if the qemu
clipboard data was not migrated, this field can also be initialized
after live migration.
Could skip migrating

last_serial, cbpending:
It is necessary for the agent to function after live migration.
Should migrate.

For the last_serial, saving & loading its value to make ensure the
client receives the most recent clipboard data from the guest after
live migration.

For the cbpending, saving & loading its value aims to inform the
guest that the clipboard has been released and is now empty in
case that the guest acts strangely while supposing that the
requested data can be properly retrieved.

To summarize, all we need to do is migrate the caps, last_serial
and cbpendings fields of the struct VDAgentChardev,

Please review, thanks

Yong

Hyman Huang (3):
  vdagent: Wrap vdagent_register_to_qemu_clipboard function
  vdagent: Set up mouse and clipboard after live migration
  vdagent: Drop blocker to support migration

 ui/trace-events |   1 +
 ui/vdagent.c    | 102 +++++++++++++++++++++++++++++++++++++++---------
 2 files changed, 85 insertions(+), 18 deletions(-)

-- 
2.27.0

[RFC 1/3] vdagent: Wrap vdagent_register_to_qemu_clipboard function

[yong.huang]

From: Hyman Huang <yong.huang@smartx.com>

For direct use in the upcoming commit, wrap the vdagent
registry logic as vdagent_register_to_qemu_clipboard.

Meanwhile, add a trace event for vdagent_recv_caps.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
---
 ui/trace-events |  1 +
 ui/vdagent.c    | 23 ++++++++++++++++-------
 2 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/ui/trace-events b/ui/trace-events
index 3da0d5e280..427a8383cb 100644
--- a/ui/trace-events
+++ b/ui/trace-events
@@ -140,6 +140,7 @@ vdagent_send(const char *name) "msg %s"
 vdagent_send_empty_clipboard(void) ""
 vdagent_recv_chunk(uint32_t size) "size %d"
 vdagent_recv_msg(const char *name, uint32_t size) "msg %s, size %d"
+vdagent_recv_caps(uint32_t caps) "received caps %u"
 vdagent_peer_cap(const char *name) "cap %s"
 vdagent_cb_grab_selection(const char *name) "selection %s"
 vdagent_cb_grab_discard(const char *name, int cur, int recv) "selection %s, cur:%d recv:%d"
diff --git a/ui/vdagent.c b/ui/vdagent.c
index 724eff972f..7a1cf674d0 100644
--- a/ui/vdagent.c
+++ b/ui/vdagent.c
@@ -694,6 +694,18 @@ static void vdagent_chr_open(Chardev *chr,
     *be_opened = true;
 }
 
+static void vdagent_register_to_qemu_clipboard(VDAgentChardev *vd)
+{
+    if (vd->cbpeer.notifier.notify == NULL) {
+        qemu_clipboard_reset_serial();
+
+        vd->cbpeer.name = "vdagent";
+        vd->cbpeer.notifier.notify = vdagent_clipboard_notify;
+        vd->cbpeer.request = vdagent_clipboard_request;
+        qemu_clipboard_peer_register(&vd->cbpeer);
+    }
+}
+
 static void vdagent_chr_recv_caps(VDAgentChardev *vd, VDAgentMessage *msg)
 {
     VDAgentAnnounceCapabilities *caps = (void *)msg->data;
@@ -711,6 +723,8 @@ static void vdagent_chr_recv_caps(VDAgentChardev *vd, VDAgentMessage *msg)
     }
 
     vd->caps = caps->caps[0];
+    trace_vdagent_recv_caps(vd->caps);
+
     if (caps->request) {
         vdagent_send_caps(vd, false);
     }
@@ -720,13 +734,8 @@ static void vdagent_chr_recv_caps(VDAgentChardev *vd, VDAgentMessage *msg)
 
     memset(vd->last_serial, 0, sizeof(vd->last_serial));
 
-    if (have_clipboard(vd) && vd->cbpeer.notifier.notify == NULL) {
-        qemu_clipboard_reset_serial();
-
-        vd->cbpeer.name = "vdagent";
-        vd->cbpeer.notifier.notify = vdagent_clipboard_notify;
-        vd->cbpeer.request = vdagent_clipboard_request;
-        qemu_clipboard_peer_register(&vd->cbpeer);
+    if (have_clipboard(vd)) {
+        vdagent_register_to_qemu_clipboard(vd);
     }
 }
 
-- 
2.27.0

[RFC 2/3] vdagent: Set up mouse and clipboard after live migration

[yong.huang]

From: Hyman Huang <yong.huang@smartx.com>

The struct VDAgentChardev's caps, last_serial, and cbpending
fields need to be migrated in order to allow live migration
for vdagent. And the clipboard and mouse should be configured
to correspond with the previously negotiated caps on the
destination.

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
---
 ui/vdagent.c | 68 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

diff --git a/ui/vdagent.c b/ui/vdagent.c
index 7a1cf674d0..4635e8fa56 100644
--- a/ui/vdagent.c
+++ b/ui/vdagent.c
@@ -7,6 +7,7 @@
 #include "qemu/units.h"
 #include "hw/qdev-core.h"
 #include "migration/blocker.h"
+#include "migration/vmstate.h"
 #include "ui/clipboard.h"
 #include "ui/console.h"
 #include "ui/input.h"
@@ -912,6 +913,72 @@ static void vdagent_chr_parse(QemuOpts *opts, ChardevBackend *backend,
     cfg->clipboard = qemu_opt_get_bool(opts, "clipboard", VDAGENT_CLIPBOARD_DEFAULT);
 }
 
+static void vdagent_release_clipboard_all_types(VDAgentChardev *vd,
+                                                QemuClipboardSelection s)
+{
+    uint32_t type;
+
+    for (type = 0; type < QEMU_CLIPBOARD_TYPE__COUNT; type++) {
+        if (vd->cbpending[s] & (1 << type)) {
+            vd->cbpending[s] &= ~(1 << type);
+            g_autofree VDAgentMessage *msg =
+                g_malloc0(sizeof(VDAgentMessage) + sizeof(uint32_t));
+
+            uint8_t *selection = msg->data;
+            *selection = s;
+            msg->size += sizeof(uint32_t);
+            msg->type = VD_AGENT_CLIPBOARD_RELEASE;
+
+            vdagent_send_msg(vd, msg);
+        }
+    }
+}
+
+static int vdagent_post_load(void *opaque, int version_id)
+{
+    VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(opaque);
+    QemuClipboardSelection s = QEMU_CLIPBOARD_SELECTION_CLIPBOARD;
+
+    if (vd->caps) {
+        if (have_mouse(vd)) {
+            vd->mouse_hs =
+                qemu_input_handler_register(&vd->mouse_dev,
+                                            &vdagent_mouse_handler);
+            if (vd->mouse_hs) {
+                qemu_input_handler_activate(vd->mouse_hs);
+            }
+        }
+
+        if (have_clipboard(vd)) {
+            vdagent_register_to_qemu_clipboard(vd);
+            if (have_selection(vd)) {
+                for (; s < QEMU_CLIPBOARD_SELECTION__COUNT; s++) {
+                    vdagent_release_clipboard_all_types(vd, s);
+                }
+            } else {
+                vdagent_release_clipboard_all_types(vd, s);
+            }
+        }
+    }
+
+    return 0;
+}
+
+static const VMStateDescription vmstate_vdagent = {
+    .name = "vdagent",
+    .version_id = 1,
+    .minimum_version_id = 1,
+    .post_load = vdagent_post_load,
+    .fields = (VMStateField[]){
+        VMSTATE_UINT32(caps, VDAgentChardev),
+        VMSTATE_UINT32_ARRAY(last_serial, VDAgentChardev,
+                QEMU_CLIPBOARD_SELECTION__COUNT),
+        VMSTATE_UINT32_ARRAY(cbpending, VDAgentChardev,
+                QEMU_CLIPBOARD_SELECTION__COUNT),
+        VMSTATE_END_OF_LIST()
+    }
+};
+
 /* ------------------------------------------------------------------ */
 
 static void vdagent_chr_class_init(ObjectClass *oc, void *data)
@@ -930,6 +997,7 @@ static void vdagent_chr_init(Object *obj)
     VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(obj);
 
     buffer_init(&vd->outbuf, "vdagent-outbuf");
+    vmstate_register(NULL, 0, &vmstate_vdagent, vd);
     error_setg(&vd->migration_blocker,
                "The vdagent chardev doesn't yet support migration");
 }
-- 
2.27.0

[RFC 3/3] vdagent: Drop blocker to support migration

[yong.huang]

From: Hyman Huang <yong.huang@smartx.com>

Signed-off-by: Hyman Huang <yong.huang@smartx.com>
---
 ui/vdagent.c | 11 -----------
 1 file changed, 11 deletions(-)

diff --git a/ui/vdagent.c b/ui/vdagent.c
index 4635e8fa56..36b0568135 100644
--- a/ui/vdagent.c
+++ b/ui/vdagent.c
@@ -6,7 +6,6 @@
 #include "qemu/option.h"
 #include "qemu/units.h"
 #include "hw/qdev-core.h"
-#include "migration/blocker.h"
 #include "migration/vmstate.h"
 #include "ui/clipboard.h"
 #include "ui/console.h"
@@ -33,9 +32,6 @@
 struct VDAgentChardev {
     Chardev parent;
 
-    /* TODO: migration isn't yet supported */
-    Error *migration_blocker;
-
     /* config */
     bool mouse;
     bool clipboard;
@@ -673,10 +669,6 @@ static void vdagent_chr_open(Chardev *chr,
     return;
 #endif
 
-    if (migrate_add_blocker(&vd->migration_blocker, errp) != 0) {
-        return;
-    }
-
     vd->mouse = VDAGENT_MOUSE_DEFAULT;
     if (cfg->has_mouse) {
         vd->mouse = cfg->mouse;
@@ -998,15 +990,12 @@ static void vdagent_chr_init(Object *obj)
 
     buffer_init(&vd->outbuf, "vdagent-outbuf");
     vmstate_register(NULL, 0, &vmstate_vdagent, vd);
-    error_setg(&vd->migration_blocker,
-               "The vdagent chardev doesn't yet support migration");
 }
 
 static void vdagent_chr_fini(Object *obj)
 {
     VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(obj);
 
-    migrate_del_blocker(&vd->migration_blocker);
     vdagent_disconnect(vd);
     if (vd->mouse_hs) {
         qemu_input_handler_unregister(vd->mouse_hs);
-- 
2.27.0

Re: [RFC 0/3] Support live migration for qemu-vdagent chardev

[Marc-André Lureau]

Hi

On Fri, Mar 21, 2025 at 7:40 AM <yong.huang@smartx.com> wrote:
>
> From: Hyman Huang <yong.huang@smartx.com>
>
> Our goal is to migrate VMs that are configured with qemu-vdagent-typed
> chardev while allowing the agent to continue working without having
> to restart the service in guest.
>

I sent a more complete series last week: "[PATCH for-10.1 00/10]
Support vdagent migration"
https://patchew.org/QEMU/20250311155932.1472092-1-marcandre.lureau@redhat.com/



> Let's justify which fields should be taken into account for struct
> VDAgentChardev.
>
> struct VDAgentChardev {
>     Chardev parent;
>
>     /* config */
>     bool mouse;
>     bool clipboard;
>
>     /* guest vdagent */
>     uint32_t caps;
>     VDIChunkHeader chunk;
>     uint32_t chunksize;
>     uint8_t *msgbuf;
>     uint32_t msgsize;
>     uint8_t *xbuf;
>     uint32_t xoff, xsize;
>     Buffer outbuf;
>
>     /* mouse */
>     DeviceState mouse_dev;
>     uint32_t mouse_x;
>     uint32_t mouse_y;
>     uint32_t mouse_btn;
>     uint32_t mouse_display;
>     QemuInputHandlerState *mouse_hs;
>
>     /* clipboard */
>     QemuClipboardPeer cbpeer;
>     uint32_t last_serial[QEMU_CLIPBOARD_SELECTION__COUNT];
>     uint32_t cbpending[QEMU_CLIPBOARD_SELECTION__COUNT];
> };
>
> parent:
> No dynamic information is generated. skip migrating.
>
> mouse, clipboard:
> The mouse and clipboard should be set up identically on both sides.
> Skip migrating.
>
> caps:
> Store the negotiated caps between the client and the guest.
> Should migrate.
>
> chunk, ... outbuf:
> The spice agent protocol's message transportation between the client
> and the guest is implemented using all of these fields, however the
> message loss can be tolerated by guests because the issue may occur
> in the real world as well.
> Could skip migrating.

It's part of the host/guest state, data will be lost and it's likely
the communication will break if it's not migrated.

>
> mouse_dev, ... mouse_hs:
> The mouse state can be reset after a live migration since the agent
> working inside the guest does not heavily depend on them.
> Could skip migrating

same

> cbpeer:
> Since the cbpeer would lose the data it references to if the qemu
> clipboard data was not migrated, this field can also be initialized
> after live migration.
> Could skip migrating
>

We should migrate the clipboard content too, to avoid having to
request it again, or have a noticeable effect.

> last_serial, cbpending:
> It is necessary for the agent to function after live migration.
> Should migrate.
>
> For the last_serial, saving & loading its value to make ensure the
> client receives the most recent clipboard data from the guest after
> live migration.
>
> For the cbpending, saving & loading its value aims to inform the
> guest that the clipboard has been released and is now empty in
> case that the guest acts strangely while supposing that the
> requested data can be properly retrieved.
>
> To summarize, all we need to do is migrate the caps, last_serial
> and cbpendings fields of the struct VDAgentChardev,
>
> Please review, thanks
>
> Yong
>
> Hyman Huang (3):
>   vdagent: Wrap vdagent_register_to_qemu_clipboard function
>   vdagent: Set up mouse and clipboard after live migration
>   vdagent: Drop blocker to support migration
>
>  ui/trace-events |   1 +
>  ui/vdagent.c    | 102 +++++++++++++++++++++++++++++++++++++++---------
>  2 files changed, 85 insertions(+), 18 deletions(-)
>
> --
> 2.27.0
>

Re: [RFC 0/3] Support live migration for qemu-vdagent chardev

[Yong Huang]

[-- Attachment #1: Type: text/plain, Size: 4119 bytes --]

On Fri, Mar 21, 2025 at 2:42 PM Marc-André Lureau <
marcandre.lureau@redhat.com> wrote:

> Hi
>
> On Fri, Mar 21, 2025 at 7:40 AM <yong.huang@smartx.com> wrote:
> >
> > From: Hyman Huang <yong.huang@smartx.com>
> >
> > Our goal is to migrate VMs that are configured with qemu-vdagent-typed
> > chardev while allowing the agent to continue working without having
> > to restart the service in guest.
> >
>
> I sent a more complete series last week: "[PATCH for-10.1 00/10]
> Support vdagent migration"
>
> https://patchew.org/QEMU/20250311155932.1472092-1-marcandre.lureau@redhat.com/


Thanks for your reminder, indeed, it migrates the qemu clipboard content
as well, more complete.

Thanks for the work, we'll pick your patchset and try it.


>
>
>
> > Let's justify which fields should be taken into account for struct
> > VDAgentChardev.
> >
> > struct VDAgentChardev {
> >     Chardev parent;
> >
> >     /* config */
> >     bool mouse;
> >     bool clipboard;
> >
> >     /* guest vdagent */
> >     uint32_t caps;
> >     VDIChunkHeader chunk;
> >     uint32_t chunksize;
> >     uint8_t *msgbuf;
> >     uint32_t msgsize;
> >     uint8_t *xbuf;
> >     uint32_t xoff, xsize;
> >     Buffer outbuf;
> >
> >     /* mouse */
> >     DeviceState mouse_dev;
> >     uint32_t mouse_x;
> >     uint32_t mouse_y;
> >     uint32_t mouse_btn;
> >     uint32_t mouse_display;
> >     QemuInputHandlerState *mouse_hs;
> >
> >     /* clipboard */
> >     QemuClipboardPeer cbpeer;
> >     uint32_t last_serial[QEMU_CLIPBOARD_SELECTION__COUNT];
> >     uint32_t cbpending[QEMU_CLIPBOARD_SELECTION__COUNT];
> > };
> >
> > parent:
> > No dynamic information is generated. skip migrating.
> >
> > mouse, clipboard:
> > The mouse and clipboard should be set up identically on both sides.
> > Skip migrating.
> >
> > caps:
> > Store the negotiated caps between the client and the guest.
> > Should migrate.
> >
> > chunk, ... outbuf:
> > The spice agent protocol's message transportation between the client
> > and the guest is implemented using all of these fields, however the
> > message loss can be tolerated by guests because the issue may occur
> > in the real world as well.
> > Could skip migrating.
>
> It's part of the host/guest state, data will be lost and it's likely
> the communication will break if it's not migrated.
>
> >
> > mouse_dev, ... mouse_hs:
> > The mouse state can be reset after a live migration since the agent
> > working inside the guest does not heavily depend on them.
> > Could skip migrating
>
> same
>
> > cbpeer:
> > Since the cbpeer would lose the data it references to if the qemu
> > clipboard data was not migrated, this field can also be initialized
> > after live migration.
> > Could skip migrating
> >
>
> We should migrate the clipboard content too, to avoid having to
> request it again, or have a noticeable effect.
>
> > last_serial, cbpending:
> > It is necessary for the agent to function after live migration.
> > Should migrate.
> >
> > For the last_serial, saving & loading its value to make ensure the
> > client receives the most recent clipboard data from the guest after
> > live migration.
> >
> > For the cbpending, saving & loading its value aims to inform the
> > guest that the clipboard has been released and is now empty in
> > case that the guest acts strangely while supposing that the
> > requested data can be properly retrieved.
> >
> > To summarize, all we need to do is migrate the caps, last_serial
> > and cbpendings fields of the struct VDAgentChardev,
> >
> > Please review, thanks
> >
> > Yong
> >
> > Hyman Huang (3):
> >   vdagent: Wrap vdagent_register_to_qemu_clipboard function
> >   vdagent: Set up mouse and clipboard after live migration
> >   vdagent: Drop blocker to support migration
> >
> >  ui/trace-events |   1 +
> >  ui/vdagent.c    | 102 +++++++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 85 insertions(+), 18 deletions(-)
> >
> > --
> > 2.27.0
> >
>
>

-- 
Best regards

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