[Qemu-devel] [PATCH 0/3] virtio-9p: hotplug and migration support

[Qemu-devel] [PATCH 0/3] virtio-9p: hotplug and migration support

[Greg Kurz]

This series brings both hoplug and migration support to virtio-9p devices.

Patch 1 is preliminary work.
Patch 2 brings hotplug and fixes a QEMU crash.
Patch 3 brings migration (of course it still depends on the 9p to be unmounted)

---

Greg Kurz (3):
      virtio-9p-coth: add release function and fix init error path
      virtio-9p: add unrealize handler
      virtio-9p: add savem handlers


 hw/9pfs/virtio-9p-coth.c   |   13 +++++++++----
 hw/9pfs/virtio-9p-coth.h   |    1 +
 hw/9pfs/virtio-9p-device.c |   24 ++++++++++++++++++++++++
 3 files changed, 34 insertions(+), 4 deletions(-)

[Qemu-devel] [PATCH 1/3] virtio-9p-coth: add release function and fix init error path

[Greg Kurz]

This is preliminary work to support hotplug/unplug of virtio-9p-device.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p-coth.c |   13 +++++++++----
 hw/9pfs/virtio-9p-coth.h |    1 +
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/hw/9pfs/virtio-9p-coth.c b/hw/9pfs/virtio-9p-coth.c
index 8185c533c013..a4392586c9a2 100644
--- a/hw/9pfs/virtio-9p-coth.c
+++ b/hw/9pfs/virtio-9p-coth.c
@@ -66,10 +66,7 @@ int v9fs_init_worker_threads(void)
     }
     p->completed = g_async_queue_new();
     if (!p->completed) {
-        /*
-         * We are going to terminate.
-         * So don't worry about cleanup
-         */
+        g_thread_pool_free(p->pool, true, true);
         ret = -1;
         goto err_out;
     }
@@ -80,3 +77,11 @@ err_out:
     pthread_sigmask(SIG_SETMASK, &oldset, NULL);
     return ret;
 }
+
+int v9fs_release_worker_threads(void)
+{
+        V9fsThPool *p = &v9fs_pool;
+
+        g_thread_pool_free(p->pool, TRUE, TRUE);
+        g_async_queue_unref(p->completed);
+}
diff --git a/hw/9pfs/virtio-9p-coth.h b/hw/9pfs/virtio-9p-coth.h
index 4f51b250d1d4..6502e422cea8 100644
--- a/hw/9pfs/virtio-9p-coth.h
+++ b/hw/9pfs/virtio-9p-coth.h
@@ -56,6 +56,7 @@ typedef struct V9fsThPool {
 
 extern void co_run_in_worker_bh(void *);
 extern int v9fs_init_worker_threads(void);
+extern int v9fs_release_worker_threads(void);
 extern int v9fs_co_readlink(V9fsPDU *, V9fsPath *, V9fsString *);
 extern int v9fs_co_readdir_r(V9fsPDU *, V9fsFidState *,
                            struct dirent *, struct dirent **result);

[Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Greg Kurz]

If the user tries to hot unplug a virtio-9p device, it seems to succeed but
in fact:
- virtio-9p coroutines thread pool and async queue are leaked
- QEMU crashes in virtio_vmstate_change() if the user tries to live migrate

This patch brings hot unplug support to virtio-9p-device. It fixes both
above issues.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index 93a407c45926..ed133c40493a 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -138,6 +138,17 @@ out:
     v9fs_path_free(&path);
 }
 
+static void virtio_9p_device_unrealize(DeviceState *dev, Error **errp)
+{
+    VirtIODevice *vdev = VIRTIO_DEVICE(dev);
+    V9fsState *s = VIRTIO_9P(dev);
+
+    v9fs_release_worker_threads();
+    g_free(s->ctx.fs_root);
+    g_free(s->tag);
+    virtio_cleanup(vdev);
+}
+
 /* virtio-9p device */
 
 static Property virtio_9p_properties[] = {
@@ -154,6 +165,7 @@ static void virtio_9p_class_init(ObjectClass *klass, void *data)
     dc->props = virtio_9p_properties;
     set_bit(DEVICE_CATEGORY_STORAGE, dc->categories);
     vdc->realize = virtio_9p_device_realize;
+    vdc->unrealize = virtio_9p_device_unrealize;
     vdc->get_features = virtio_9p_get_features;
     vdc->get_config = virtio_9p_get_config;
 }

[Qemu-devel] [PATCH 3/3] virtio-9p: add savem handlers

[Greg Kurz]

We don't support migration of mounted 9p shares. This is handled by a
migration blocker.

One would expect, however, to be able to migrate if the share is unmounted.
Unfortunately virtio-9p-device does not register savevm handlers at all !
Migration succeeds and leaves the guest with a dangling device...

This patch simply registers migration handlers for virtio-9p-device. Whether
migration is possible or not still depends on the migration blocker.

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---
 hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/hw/9pfs/virtio-9p-device.c b/hw/9pfs/virtio-9p-device.c
index ed133c40493a..bd7f10a0a902 100644
--- a/hw/9pfs/virtio-9p-device.c
+++ b/hw/9pfs/virtio-9p-device.c
@@ -43,6 +43,16 @@ static void virtio_9p_get_config(VirtIODevice *vdev, uint8_t *config)
     g_free(cfg);
 }
 
+static void virtio_9p_save(QEMUFile *f, void *opaque)
+{
+    virtio_save(VIRTIO_DEVICE(opaque), f);
+}
+
+static int virtio_9p_load(QEMUFile *f, void *opaque, int version_id)
+{
+    return virtio_load(VIRTIO_DEVICE(opaque), f, version_id);
+}
+
 static void virtio_9p_device_realize(DeviceState *dev, Error **errp)
 {
     VirtIODevice *vdev = VIRTIO_DEVICE(dev);
@@ -130,6 +140,7 @@ static void virtio_9p_device_realize(DeviceState *dev, Error **errp)
     }
     v9fs_path_free(&path);
 
+    register_savevm(dev, "virtio-9p", -1, 1, virtio_9p_save, virtio_9p_load, s);
     return;
 out:
     g_free(s->ctx.fs_root);
@@ -146,6 +157,7 @@ static void virtio_9p_device_unrealize(DeviceState *dev, Error **errp)
     v9fs_release_worker_threads();
     g_free(s->ctx.fs_root);
     g_free(s->tag);
+    unregister_savevm(dev, "virtio-9p", s);
     virtio_cleanup(vdev);
 }
 

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Stefan Hajnoczi]

On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> in fact:
> - virtio-9p coroutines thread pool and async queue are leaked
> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> 
> This patch brings hot unplug support to virtio-9p-device. It fixes both
> above issues.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---
>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
>  1 file changed, 12 insertions(+)

What happens to in-flight I/O requests?  We cannot assume that the guest
driver quiesces the device.

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Greg Kurz]

On Tue, 6 Oct 2015 09:09:14 +0100
Stefan Hajnoczi <stefanha@gmail.com> wrote:

> On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> > If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> > in fact:
> > - virtio-9p coroutines thread pool and async queue are leaked
> > - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> > 
> > This patch brings hot unplug support to virtio-9p-device. It fixes both
> > above issues.
> > 
> > Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > ---
> >  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
> >  1 file changed, 12 insertions(+)
> 
> What happens to in-flight I/O requests?  We cannot assume that the guest
> driver quiesces the device.
> 

We can assume that the guest has unmounted the 9p share otherwise migration
is blocked... is it possible we still have in-flight I/O requests in this
scenario ?

Re: [Qemu-devel] [PATCH 1/3] virtio-9p-coth: add release function and fix init error path

[Greg Kurz]

On Mon, 05 Oct 2015 11:07:16 +0200
Greg Kurz <gkurz@linux.vnet.ibm.com> wrote:

> This is preliminary work to support hotplug/unplug of virtio-9p-device.
> 
> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> ---

Hmm... still not good. Since this is shared by all virtio-9p devices, we need
at least a refcount.

>  hw/9pfs/virtio-9p-coth.c |   13 +++++++++----
>  hw/9pfs/virtio-9p-coth.h |    1 +
>  2 files changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/hw/9pfs/virtio-9p-coth.c b/hw/9pfs/virtio-9p-coth.c
> index 8185c533c013..a4392586c9a2 100644
> --- a/hw/9pfs/virtio-9p-coth.c
> +++ b/hw/9pfs/virtio-9p-coth.c
> @@ -66,10 +66,7 @@ int v9fs_init_worker_threads(void)
>      }
>      p->completed = g_async_queue_new();
>      if (!p->completed) {
> -        /*
> -         * We are going to terminate.
> -         * So don't worry about cleanup
> -         */
> +        g_thread_pool_free(p->pool, true, true);
>          ret = -1;
>          goto err_out;
>      }
> @@ -80,3 +77,11 @@ err_out:
>      pthread_sigmask(SIG_SETMASK, &oldset, NULL);
>      return ret;
>  }
> +
> +int v9fs_release_worker_threads(void)
> +{
> +        V9fsThPool *p = &v9fs_pool;
> +
> +        g_thread_pool_free(p->pool, TRUE, TRUE);
> +        g_async_queue_unref(p->completed);
> +}
> diff --git a/hw/9pfs/virtio-9p-coth.h b/hw/9pfs/virtio-9p-coth.h
> index 4f51b250d1d4..6502e422cea8 100644
> --- a/hw/9pfs/virtio-9p-coth.h
> +++ b/hw/9pfs/virtio-9p-coth.h
> @@ -56,6 +56,7 @@ typedef struct V9fsThPool {
> 
>  extern void co_run_in_worker_bh(void *);
>  extern int v9fs_init_worker_threads(void);
> +extern int v9fs_release_worker_threads(void);
>  extern int v9fs_co_readlink(V9fsPDU *, V9fsPath *, V9fsString *);
>  extern int v9fs_co_readdir_r(V9fsPDU *, V9fsFidState *,
>                             struct dirent *, struct dirent **result);
> 
> 

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Aneesh Kumar K.V]

Stefan Hajnoczi <stefanha@gmail.com> writes:

> On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
>> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
>> in fact:
>> - virtio-9p coroutines thread pool and async queue are leaked
>> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
>> 
>> This patch brings hot unplug support to virtio-9p-device. It fixes both
>> above issues.
>> 
>> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
>> ---
>>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
>>  1 file changed, 12 insertions(+)
>
> What happens to in-flight I/O requests?  We cannot assume that the guest
> driver quiesces the device.

We enable migration blocker when we have an active mount. So if we get
here, that should indicate no active 9p mounts.

-aneesh

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Greg Kurz]

On Wed, 07 Oct 2015 14:20:28 +0530
"Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:

> Stefan Hajnoczi <stefanha@gmail.com> writes:
> 
> > On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> >> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> >> in fact:
> >> - virtio-9p coroutines thread pool and async queue are leaked
> >> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> >> 
> >> This patch brings hot unplug support to virtio-9p-device. It fixes both
> >> above issues.
> >> 
> >> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> >> ---
> >>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
> >>  1 file changed, 12 insertions(+)
> >
> > What happens to in-flight I/O requests?  We cannot assume that the guest
> > driver quiesces the device.
> 
> We enable migration blocker when we have an active mount. So if we get
> here, that should indicate no active 9p mounts.
> 
> -aneesh

Oops.. Stefan is talking about hot-unplug versus in-flight requests... not
about migration. And there is no such thing as a hot-unplug blocker...

--
Greg

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Michael S. Tsirkin]

On Fri, Oct 09, 2015 at 09:23:49AM +0200, Greg Kurz wrote:
> On Wed, 07 Oct 2015 14:20:28 +0530
> "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> 
> > Stefan Hajnoczi <stefanha@gmail.com> writes:
> > 
> > > On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> > >> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> > >> in fact:
> > >> - virtio-9p coroutines thread pool and async queue are leaked
> > >> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> > >> 
> > >> This patch brings hot unplug support to virtio-9p-device. It fixes both
> > >> above issues.
> > >> 
> > >> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > >> ---
> > >>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
> > >>  1 file changed, 12 insertions(+)
> > >
> > > What happens to in-flight I/O requests?  We cannot assume that the guest
> > > driver quiesces the device.
> > 
> > We enable migration blocker when we have an active mount. So if we get
> > here, that should indicate no active 9p mounts.
> > 
> > -aneesh
> 
> Oops.. Stefan is talking about hot-unplug versus in-flight requests... not
> about migration. And there is no such thing as a hot-unplug blocker...

If unplug request fails, that should be enough.

> --
> Greg

Re: [Qemu-devel] [PATCH 2/3] virtio-9p: add unrealize handler

[Greg Kurz]

On Fri, 9 Oct 2015 10:36:56 +0300
"Michael S. Tsirkin" <mst@redhat.com> wrote:

> On Fri, Oct 09, 2015 at 09:23:49AM +0200, Greg Kurz wrote:
> > On Wed, 07 Oct 2015 14:20:28 +0530
> > "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com> wrote:
> > 
> > > Stefan Hajnoczi <stefanha@gmail.com> writes:
> > > 
> > > > On Mon, Oct 05, 2015 at 11:07:23AM +0200, Greg Kurz wrote:
> > > >> If the user tries to hot unplug a virtio-9p device, it seems to succeed but
> > > >> in fact:
> > > >> - virtio-9p coroutines thread pool and async queue are leaked
> > > >> - QEMU crashes in virtio_vmstate_change() if the user tries to live migrate
> > > >> 
> > > >> This patch brings hot unplug support to virtio-9p-device. It fixes both
> > > >> above issues.
> > > >> 
> > > >> Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
> > > >> ---
> > > >>  hw/9pfs/virtio-9p-device.c |   12 ++++++++++++
> > > >>  1 file changed, 12 insertions(+)
> > > >
> > > > What happens to in-flight I/O requests?  We cannot assume that the guest
> > > > driver quiesces the device.
> > > 
> > > We enable migration blocker when we have an active mount. So if we get
> > > here, that should indicate no active 9p mounts.
> > > 
> > > -aneesh
> > 
> > Oops.. Stefan is talking about hot-unplug versus in-flight requests... not
> > about migration. And there is no such thing as a hot-unplug blocker...
> 
> If unplug request fails, that should be enough.
> 

Like setting @hotpluggable to false for the virtio-9p-pci class ? I see no
other way for the unplug request to fail... but I will happily accept all
suggestions :)

--
Greg