Re: [Qemu-devel] [PATCH v2 3/4] migration: disallow migrate_add

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Re: [Qemu-devel] [PATCH v2 3/4] migration: disallow migrate_add_blocker

From:	Ashijeet Acharya
Subject:	Re: [Qemu-devel] [PATCH v2 3/4] migration: disallow migrate_add_blocker during migration
Date:	Sun, 8 Jan 2017 13:04:47 +0530
On Friday, January 6, 2017, Greg Kurz <address@hidden> wrote:

> Hi Ashijeet,
>

Hello Greg,


> I didn't think hard enough while reviewing the changes for hw/9pfs/9p.c...
> I have
> some more remarks, sorry... :-/
>
> No problem, I will send an updated v4 for these.

On Wed,  4 Jan 2017 18:02:28 +0530
> Ashijeet Acharya <address@hidden <javascript:;>> wrote:
>
> > If a migration is already in progress and somebody attempts
> > to add a migration blocker, this should rightly fail.
> >
> > Add an errp parameter and a retcode return value to migrate_add_blocker.
> >
> > Signed-off-by: John Snow <address@hidden <javascript:;>>
> > Signed-off-by: Ashijeet Acharya <address@hidden
> <javascript:;>>
> > ---
> >  block/qcow.c                  |  6 +++++-
> >  block/vdi.c                   |  6 +++++-
> >  block/vhdx.c                  | 16 ++++++++++------
> >  block/vmdk.c                  |  7 ++++++-
> >  block/vpc.c                   | 10 +++++++---
> >  block/vvfat.c                 | 20 ++++++++++++--------
> >  hw/9pfs/9p.c                  | 20 +++++++++++++++-----
> >  hw/display/virtio-gpu.c       | 29 ++++++++++++++++-------------
> >  hw/intc/arm_gic_kvm.c         | 16 ++++++++++------
> >  hw/intc/arm_gicv3_its_kvm.c   | 18 +++++++++++-------
> >  hw/intc/arm_gicv3_kvm.c       | 19 ++++++++++++-------
> >  hw/misc/ivshmem.c             | 11 +++++++----
> >  hw/scsi/vhost-scsi.c          | 25 +++++++++++++++++++------
> >  hw/virtio/vhost.c             |  8 +++++++-
> >  include/migration/migration.h |  6 +++++-
> >  migration/migration.c         | 35 +++++++++++++++++++++++++++++++++--
> >  stubs/migr-blocker.c          |  3 ++-
> >  target-i386/kvm.c             | 16 +++++++++++++---
> >  18 files changed, 195 insertions(+), 76 deletions(-)
> >
> > diff --git a/block/qcow.c b/block/qcow.c
> > index 7540f43..11526a1 100644
> > --- a/block/qcow.c
> > +++ b/block/qcow.c
> > @@ -252,7 +252,11 @@ static int qcow_open(BlockDriverState *bs, QDict
> *options, int flags,
> >      error_setg(&s->migration_blocker, "The qcow format used by node
> '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> >
> >      qemu_co_mutex_init(&s->lock);
> >      return 0;
> > diff --git a/block/vdi.c b/block/vdi.c
> > index 96b78d5..2b56f52 100644
> > --- a/block/vdi.c
> > +++ b/block/vdi.c
> > @@ -471,7 +471,11 @@ static int vdi_open(BlockDriverState *bs, QDict
> *options, int flags,
> >      error_setg(&s->migration_blocker, "The vdi format used by node
> '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail_free_bmap;
> > +    }
> >
> >      qemu_co_mutex_init(&s->write_lock);
> >
> > diff --git a/block/vhdx.c b/block/vhdx.c
> > index 0ba2f0a..d81941b 100644
> > --- a/block/vhdx.c
> > +++ b/block/vhdx.c
> > @@ -991,6 +991,16 @@ static int vhdx_open(BlockDriverState *bs, QDict
> *options, int flags,
> >          }
> >      }
> >
> > +    /* Disable migration when VHDX images are used */
> > +    error_setg(&s->migration_blocker, "The vhdx format used by node
> '%s' "
> > +               "does not support live migration",
> > +               bdrv_get_device_or_node_name(bs));
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> >      if (flags & BDRV_O_RDWR) {
> >          ret = vhdx_update_headers(bs, s, false, NULL);
> >          if (ret < 0) {
> > @@ -1000,12 +1010,6 @@ static int vhdx_open(BlockDriverState *bs, QDict
> *options, int flags,
> >
> >      /* TODO: differencing files */
> >
> > -    /* Disable migration when VHDX images are used */
> > -    error_setg(&s->migration_blocker, "The vhdx format used by node
> '%s' "
> > -               "does not support live migration",
> > -               bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > -
> >      return 0;
> >  fail:
> >      vhdx_close(bs);
> > diff --git a/block/vmdk.c b/block/vmdk.c
> > index a11c27a..4a45a83 100644
> > --- a/block/vmdk.c
> > +++ b/block/vmdk.c
> > @@ -976,7 +976,12 @@ static int vmdk_open(BlockDriverState *bs, QDict
> *options, int flags,
> >      error_setg(&s->migration_blocker, "The vmdk format used by node
> '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> >      g_free(buf);
> >      return 0;
> >
> > diff --git a/block/vpc.c b/block/vpc.c
> > index 8d5886f..299a8c8 100644
> > --- a/block/vpc.c
> > +++ b/block/vpc.c
> > @@ -422,13 +422,17 @@ static int vpc_open(BlockDriverState *bs, QDict
> *options, int flags,
> >  #endif
> >      }
> >
> > -    qemu_co_mutex_init(&s->lock);
> > -
> >      /* Disable migration when VHD images are used */
> >      error_setg(&s->migration_blocker, "The vpc format used by node
> '%s' "
> >                 "does not support live migration",
> >                 bdrv_get_device_or_node_name(bs));
> > -    migrate_add_blocker(s->migration_blocker);
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        goto fail;
> > +    }
> > +
> > +    qemu_co_mutex_init(&s->lock);
> >
> >      return 0;
> >
> > diff --git a/block/vvfat.c b/block/vvfat.c
> > index ded2109..3de3320 100644
> > --- a/block/vvfat.c
> > +++ b/block/vvfat.c
> > @@ -1185,22 +1185,26 @@ static int vvfat_open(BlockDriverState *bs,
> QDict *options, int flags,
> >
> >      s->sector_count = s->faked_sectors + s->sectors_per_cluster*s->
> cluster_count;
> >
> > -    if (s->first_sectors_number == 0x40) {
> > -        init_mbr(s, cyls, heads, secs);
> > -    }
> > -
> > -    //    assert(is_consistent(s));
> > -    qemu_co_mutex_init(&s->lock);
> > -
> >      /* Disable migration when vvfat is used rw */
> >      if (s->qcow) {
> >          error_setg(&s->migration_blocker,
> >                     "The vvfat (rw) format used by node '%s' "
> >                     "does not support live migration",
> >                     bdrv_get_device_or_node_name(bs));
> > -        migrate_add_blocker(s->migration_blocker);
> > +        ret = migrate_add_blocker(s->migration_blocker, errp);
> > +        if (ret < 0) {
> > +            error_free(s->migration_blocker);
> > +            goto fail;
> > +        }
> > +    }
> > +
> > +    if (s->first_sectors_number == 0x40) {
> > +        init_mbr(s, cyls, heads, secs);
> >      }
> >
> > +    //    assert(is_consistent(s));
> > +    qemu_co_mutex_init(&s->lock);
> > +
> >      ret = 0;
> >  fail:
> >      qemu_opts_del(opts);
> > diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
> > index faebd91..43cb065 100644
> > --- a/hw/9pfs/9p.c
> > +++ b/hw/9pfs/9p.c
> > @@ -1013,20 +1013,30 @@ static void coroutine_fn v9fs_attach(void
> *opaque)
> >          goto out;
> >      }
> >      err += offset;
> > -    memcpy(&s->root_qid, &qid, sizeof(qid));
> > -    trace_v9fs_attach_return(pdu->tag, pdu->id,
> > -                             qid.type, qid.version, qid.path);
> > +
> >      /*
> >       * disable migration if we haven't done already.
> >       * attach could get called multiple times for the same export.
> >       */
> >      if (!s->migration_blocker) {
> > -        s->root_fid = fid;
> > +        int ret;
> >          error_setg(&s->migration_blocker,
> >                     "Migration is disabled when VirtFS export path '%s'
> is mounted in the guest using mount_tag '%s'",
> >                     s->ctx.fs_root ? s->ctx.fs_root : "NULL", s->tag);
> > -        migrate_add_blocker(s->migration_blocker);
> > +        ret = migrate_add_blocker(s->migration_blocker, NULL);
> > +        if (ret < 0) {
> > +            err = ret;
> > +            clunk_fid(s, fid);
> > +            error_free(s->migration_blocker);
> > +            s->migration_blocker = NULL;
>
> It's better to rollback things in reverse order (i.e. clunk_fid() should
> be called here).


Done.


>
> > +            goto out;
> > +        }
> > +        s->root_fid = fid;
> >      }
>
> I now realize that all the migration blocker stuff should be done before
> we call pdu_marshal() since we may now return an error to the guest. And



Yes, migration blocker needs to be allowed to do its bit first and it might
fail and return an error.

thus, you can drop ret and use err directly.


Alright. I will drop it.

Also you suggested to use EBUSY instead of EACCES but then it will be
difficult to differentiate which case failed migration blocker as both will
end up returning the same error number.

Ashijeet


> Cheers.
>
> --
> Greg
>
> > +
> > +    memcpy(&s->root_qid, &qid, sizeof(qid));
> > +    trace_v9fs_attach_return(pdu->tag, pdu->id,
> > +                             qid.type, qid.version, qid.path);
> >  out:
> >      put_fid(pdu, fidp);
> >  out_nofid:
> > diff --git a/hw/display/virtio-gpu.c b/hw/display/virtio-gpu.c
> > index 5f32e1a..6e60b8c 100644
> > --- a/hw/display/virtio-gpu.c
> > +++ b/hw/display/virtio-gpu.c
> > @@ -1108,14 +1108,6 @@ static void virtio_gpu_device_realize(DeviceState
> *qdev, Error **errp)
> >          return;
> >      }
> >
> > -    g->config_size = sizeof(struct virtio_gpu_config);
> > -    g->virtio_config.num_scanouts = g->conf.max_outputs;
> > -    virtio_init(VIRTIO_DEVICE(g), "virtio-gpu", VIRTIO_ID_GPU,
> > -                g->config_size);
> > -
> > -    g->req_state[0].width = 1024;
> > -    g->req_state[0].height = 768;
> > -
> >      g->use_virgl_renderer = false;
> >  #if !defined(CONFIG_VIRGL) || defined(HOST_WORDS_BIGENDIAN)
> >      have_virgl = false;
> > @@ -1127,6 +1119,22 @@ static void virtio_gpu_device_realize(DeviceState
> *qdev, Error **errp)
> >      }
> >
> >      if (virtio_gpu_virgl_enabled(g->conf)) {
> > +        error_setg(&g->migration_blocker, "virgl is not yet
> migratable");
> > +        if (migrate_add_blocker(g->migration_blocker, errp) < 0) {
> > +            error_free(g->migration_blocker);
> > +            return;
> > +        }
> > +    }
> > +
> > +    g->config_size = sizeof(struct virtio_gpu_config);
> > +    g->virtio_config.num_scanouts = g->conf.max_outputs;
> > +    virtio_init(VIRTIO_DEVICE(g), "virtio-gpu", VIRTIO_ID_GPU,
> > +                g->config_size);
> > +
> > +    g->req_state[0].width = 1024;
> > +    g->req_state[0].height = 768;
> > +
> > +    if (virtio_gpu_virgl_enabled(g->conf)) {
> >          /* use larger control queue in 3d mode */
> >          g->ctrl_vq   = virtio_add_queue(vdev, 256,
> virtio_gpu_handle_ctrl_cb);
> >          g->cursor_vq = virtio_add_queue(vdev, 16,
> virtio_gpu_handle_cursor_cb);
> > @@ -1152,11 +1160,6 @@ static void virtio_gpu_device_realize(DeviceState
> *qdev, Error **errp)
> >              dpy_gfx_replace_surface(g->scanout[i].con, NULL);
> >          }
> >      }
> > -
> > -    if (virtio_gpu_virgl_enabled(g->conf)) {
> > -        error_setg(&g->migration_blocker, "virgl is not yet
> migratable");
> > -        migrate_add_blocker(g->migration_blocker);
> > -    }
> >  }
> >
> >  static void virtio_gpu_device_unrealize(DeviceState *qdev, Error
> **errp)
> > diff --git a/hw/intc/arm_gic_kvm.c b/hw/intc/arm_gic_kvm.c
> > index 11729ee..3614daa 100644
> > --- a/hw/intc/arm_gic_kvm.c
> > +++ b/hw/intc/arm_gic_kvm.c
> > @@ -510,6 +510,16 @@ static void kvm_arm_gic_realize(DeviceState *dev,
> Error **errp)
> >          return;
> >      }
> >
> > +    if (!kvm_arm_gic_can_save_restore(s)) {
> > +        error_setg(&s->migration_blocker, "This operating system
> kernel does "
> > +                                          "not support vGICv2
> migration");
> > +        ret = migrate_add_blocker(s->migration_blocker, errp);
> > +        if (ret < 0) {
> > +            error_free(s->migration_blocker);
> > +            return;
> > +        }
> > +    }
> > +
> >      gic_init_irqs_and_mmio(s, kvm_arm_gicv2_set_irq, NULL);
> >
> >      for (i = 0; i < s->num_irq - GIC_INTERNAL; i++) {
> > @@ -558,12 +568,6 @@ static void kvm_arm_gic_realize(DeviceState *dev,
> Error **errp)
> >                              KVM_VGIC_V2_ADDR_TYPE_CPU,
> >                              s->dev_fd);
> >
> > -    if (!kvm_arm_gic_can_save_restore(s)) {
> > -        error_setg(&s->migration_blocker, "This operating system
> kernel does "
> > -                                          "not support vGICv2
> migration");
> > -        migrate_add_blocker(s->migration_blocker);
> > -    }
> > -
> >      if (kvm_has_gsi_routing()) {
> >          /* set up irq routing */
> >          kvm_init_irq_routing(kvm_state);
> > diff --git a/hw/intc/arm_gicv3_its_kvm.c b/hw/intc/arm_gicv3_its_kvm.c
> > index fc246e0..950a02f 100644
> > --- a/hw/intc/arm_gicv3_its_kvm.c
> > +++ b/hw/intc/arm_gicv3_its_kvm.c
> > @@ -63,6 +63,17 @@ static void kvm_arm_its_realize(DeviceState *dev,
> Error **errp)
> >          return;
> >      }
> >
> > +    /*
> > +     * Block migration of a KVM GICv3 ITS device: the API for saving and
> > +     * restoring the state in the kernel is not yet available
> > +     */
> > +    error_setg(&s->migration_blocker, "vITS migration is not
> implemented");
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        return;
> > +    }
> > +
> >      /* explicit init of the ITS */
> >      kvm_device_access(s->dev_fd, KVM_DEV_ARM_VGIC_GRP_CTRL,
> >                        KVM_DEV_ARM_VGIC_CTRL_INIT, NULL, true);
> > @@ -73,13 +84,6 @@ static void kvm_arm_its_realize(DeviceState *dev,
> Error **errp)
> >
> >      gicv3_its_init_mmio(s, NULL);
> >
> > -    /*
> > -     * Block migration of a KVM GICv3 ITS device: the API for saving and
> > -     * restoring the state in the kernel is not yet available
> > -     */
> > -    error_setg(&s->migration_blocker, "vITS migration is not
> implemented");
> > -    migrate_add_blocker(s->migration_blocker);
> > -
> >      kvm_msi_use_devid = true;
> >      kvm_gsi_direct_mapping = false;
> >      kvm_msi_via_irqfd_allowed = kvm_irqfds_enabled();
> > diff --git a/hw/intc/arm_gicv3_kvm.c b/hw/intc/arm_gicv3_kvm.c
> > index 199a439..06f6f30 100644
> > --- a/hw/intc/arm_gicv3_kvm.c
> > +++ b/hw/intc/arm_gicv3_kvm.c
> > @@ -86,6 +86,7 @@ static void kvm_arm_gicv3_realize(DeviceState *dev,
> Error **errp)
> >      KVMARMGICv3Class *kgc = KVM_ARM_GICV3_GET_CLASS(s);
> >      Error *local_err = NULL;
> >      int i;
> > +    int ret;
> >
> >      DPRINTF("kvm_arm_gicv3_realize\n");
> >
> > @@ -110,6 +111,17 @@ static void kvm_arm_gicv3_realize(DeviceState
> *dev, Error **errp)
> >          return;
> >      }
> >
> > +    /* Block migration of a KVM GICv3 device: the API for saving and
> restoring
> > +     * the state in the kernel is not yet finalised in the kernel or
> > +     * implemented in QEMU.
> > +     */
> > +    error_setg(&s->migration_blocker, "vGICv3 migration is not
> implemented");
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        error_free(s->migration_blocker);
> > +        return;
> > +    }
> > +
> >      kvm_device_access(s->dev_fd, KVM_DEV_ARM_VGIC_GRP_NR_IRQS,
> >                        0, &s->num_irq, true);
> >
> > @@ -122,13 +134,6 @@ static void kvm_arm_gicv3_realize(DeviceState
> *dev, Error **errp)
> >      kvm_arm_register_device(&s->iomem_redist, -1,
> KVM_DEV_ARM_VGIC_GRP_ADDR,
> >                              KVM_VGIC_V3_ADDR_TYPE_REDIST, s->dev_fd);
> >
> > -    /* Block migration of a KVM GICv3 device: the API for saving and
> restoring
> > -     * the state in the kernel is not yet finalised in the kernel or
> > -     * implemented in QEMU.
> > -     */
> > -    error_setg(&s->migration_blocker, "vGICv3 migration is not
> implemented");
> > -    migrate_add_blocker(s->migration_blocker);
> > -
> >      if (kvm_has_gsi_routing()) {
> >          /* set up irq routing */
> >          kvm_init_irq_routing(kvm_state);
> > diff --git a/hw/misc/ivshmem.c b/hw/misc/ivshmem.c
> > index abeaf3d..585cc5b 100644
> > --- a/hw/misc/ivshmem.c
> > +++ b/hw/misc/ivshmem.c
> > @@ -903,9 +903,6 @@ static void ivshmem_common_realize(PCIDevice *dev,
> Error **errp)
> >          }
> >      }
> >
> > -    vmstate_register_ram(s->ivshmem_bar2, DEVICE(s));
> > -    pci_register_bar(PCI_DEVICE(s), 2, attr, s->ivshmem_bar2);
> > -
> >      if (s->master == ON_OFF_AUTO_AUTO) {
> >          s->master = s->vm_id == 0 ? ON_OFF_AUTO_ON : ON_OFF_AUTO_OFF;
> >      }
> > @@ -913,8 +910,14 @@ static void ivshmem_common_realize(PCIDevice *dev,
> Error **errp)
> >      if (!ivshmem_is_master(s)) {
> >          error_setg(&s->migration_blocker,
> >                     "Migration is disabled when using feature 'peer
> mode' in device 'ivshmem'");
> > -        migrate_add_blocker(s->migration_blocker);
> > +        if (migrate_add_blocker(s->migration_blocker, errp) < 0) {
> > +            error_free(s->migration_blocker);
> > +            return;
> > +        }
> >      }
> > +
> > +    vmstate_register_ram(s->ivshmem_bar2, DEVICE(s));
> > +    pci_register_bar(PCI_DEVICE(s), 2, attr, s->ivshmem_bar2);
> >  }
> >
> >  static void ivshmem_exit(PCIDevice *dev)
> > diff --git a/hw/scsi/vhost-scsi.c b/hw/scsi/vhost-scsi.c
> > index 5b26946..ff503d0 100644
> > --- a/hw/scsi/vhost-scsi.c
> > +++ b/hw/scsi/vhost-scsi.c
> > @@ -238,8 +238,14 @@ static void vhost_scsi_realize(DeviceState *dev,
> Error **errp)
> >                                 vhost_dummy_handle_output);
> >      if (err != NULL) {
> >          error_propagate(errp, err);
> > -        close(vhostfd);
> > -        return;
> > +        goto close_fd;
> > +    }
> > +
> > +    error_setg(&s->migration_blocker,
> > +               "vhost-scsi does not support migration");
> > +    ret = migrate_add_blocker(s->migration_blocker, errp);
> > +    if (ret < 0) {
> > +        goto free_blocker;
> >      }
> >
> >      s->dev.nvqs = VHOST_SCSI_VQ_NUM_FIXED + vs->conf.num_queues;
> > @@ -252,7 +258,7 @@ static void vhost_scsi_realize(DeviceState *dev,
> Error **errp)
> >      if (ret < 0) {
> >          error_setg(errp, "vhost-scsi: vhost initialization failed: %s",
> >                     strerror(-ret));
> > -        return;
> > +        goto free_vqs;
> >      }
> >
> >      /* At present, channel and lun both are 0 for bootable vhost-scsi
> disk */
> > @@ -261,9 +267,16 @@ static void vhost_scsi_realize(DeviceState *dev,
> Error **errp)
> >      /* Note: we can also get the minimum tpgt from kernel */
> >      s->target = vs->conf.boot_tpgt;
> >
> > -    error_setg(&s->migration_blocker,
> > -            "vhost-scsi does not support migration");
> > -    migrate_add_blocker(s->migration_blocker);
> > +    return;
> > +
> > + free_vqs:
> > +    migrate_del_blocker(s->migration_blocker);
> > +    g_free(s->dev.vqs);
> > + free_blocker:
> > +    error_free(s->migration_blocker);
> > + close_fd:
> > +    close(vhostfd);
> > +    return;
> >  }
> >
> >  static void vhost_scsi_unrealize(DeviceState *dev, Error **errp)
> > diff --git a/hw/virtio/vhost.c b/hw/virtio/vhost.c
> > index f7f7023..416fada 100644
> > --- a/hw/virtio/vhost.c
> > +++ b/hw/virtio/vhost.c
> > @@ -1157,7 +1157,13 @@ int vhost_dev_init(struct vhost_dev *hdev, void
> *opaque,
> >      }
> >
> >      if (hdev->migration_blocker != NULL) {
> > -        migrate_add_blocker(hdev->migration_blocker);
> > +        Error *local_err;
> > +        r = migrate_add_blocker(hdev->migration_blocker, &local_err);
> > +        if (r < 0) {
> > +            error_report_err(local_err);
> > +            error_free(hdev->migration_blocker);
> > +            goto fail_busyloop;
> > +        }
> >      }
> >
> >      hdev->mem = g_malloc0(offsetof(struct vhost_memory, regions));
> > diff --git a/include/migration/migration.h
> b/include/migration/migration.h
> > index 40b3697..46a4bb5 100644
> > --- a/include/migration/migration.h
> > +++ b/include/migration/migration.h
> > @@ -243,6 +243,7 @@ void remove_migration_state_change_notifier(Notifier
> *notify);
> >  MigrationState *migrate_init(const MigrationParams *params);
> >  bool migration_is_blocked(Error **errp);
> >  bool migration_in_setup(MigrationState *);
> > +bool migration_is_idle(MigrationState *s);
> >  bool migration_has_finished(MigrationState *);
> >  bool migration_has_failed(MigrationState *);
> >  /* True if outgoing migration has entered postcopy phase */
> > @@ -287,8 +288,11 @@ int ram_postcopy_incoming_init(MigrationIncomingState
> *mis);
> >   * @migrate_add_blocker - prevent migration from proceeding
> >   *
> >   * @reason - an error to be returned whenever migration is attempted
> > + * @errp - [out] The reason (if any) we cannot block migration right
> now.
> > + *
> > + * @returns - 0 on success, -EBUSY on failure, with errp set.
> >   */
> > -void migrate_add_blocker(Error *reason);
> > +int migrate_add_blocker(Error *reason, Error **errp);
> >
> >  /**
> >   * @migrate_del_blocker - remove a blocking error from migration
> > diff --git a/migration/migration.c b/migration/migration.c
> > index f498ab8..713e012 100644
> > --- a/migration/migration.c
> > +++ b/migration/migration.c
> > @@ -1044,6 +1044,31 @@ bool 
> > migration_in_postcopy_after_devices(MigrationState
> *s)
> >      return migration_in_postcopy(s) && s->postcopy_after_devices;
> >  }
> >
> > +bool migration_is_idle(MigrationState *s)
> > +{
> > +    if (!s) {
> > +        s = migrate_get_current();
> > +    }
> > +
> > +    switch (s->state) {
> > +    case MIGRATION_STATUS_NONE:
> > +    case MIGRATION_STATUS_CANCELLED:
> > +    case MIGRATION_STATUS_COMPLETED:
> > +    case MIGRATION_STATUS_FAILED:
> > +        return true;
> > +    case MIGRATION_STATUS_SETUP:
> > +    case MIGRATION_STATUS_CANCELLING:
> > +    case MIGRATION_STATUS_ACTIVE:
> > +    case MIGRATION_STATUS_POSTCOPY_ACTIVE:
> > +    case MIGRATION_STATUS_COLO:
> > +        return false;
> > +    case MIGRATION_STATUS__MAX:
> > +        g_assert_not_reached();
> > +    }
> > +
> > +    return false;
> > +}
> > +
> >  MigrationState *migrate_init(const MigrationParams *params)
> >  {
> >      MigrationState *s = migrate_get_current();
> > @@ -1086,9 +1111,15 @@ MigrationState *migrate_init(const
> MigrationParams *params)
> >
> >  static GSList *migration_blockers;
> >
> > -void migrate_add_blocker(Error *reason)
> > +int migrate_add_blocker(Error *reason, Error **errp)
> >  {
> > -    migration_blockers = g_slist_prepend(migration_blockers, reason);
> > +    if (migration_is_idle(NULL)) {
> > +        migration_blockers = g_slist_prepend(migration_blockers,
> reason);
> > +        return 0;
> > +    }
> > +
> > +    error_setg(errp, "Cannot block a migration already in-progress");
> > +    return -EBUSY;
> >  }
> >
> >  void migrate_del_blocker(Error *reason)
> > diff --git a/stubs/migr-blocker.c b/stubs/migr-blocker.c
> > index 8ab3604..a5ba18f 100644
> > --- a/stubs/migr-blocker.c
> > +++ b/stubs/migr-blocker.c
> > @@ -2,8 +2,9 @@
> >  #include "qemu-common.h"
> >  #include "migration/migration.h"
> >
> > -void migrate_add_blocker(Error *reason)
> > +int migrate_add_blocker(Error *reason, Error **errp)
> >  {
> > +    return 0;
> >  }
> >
> >  void migrate_del_blocker(Error *reason)
> > diff --git a/target-i386/kvm.c b/target-i386/kvm.c
> > index f62264a..6031a1c 100644
> > --- a/target-i386/kvm.c
> > +++ b/target-i386/kvm.c
> > @@ -961,7 +961,11 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >          error_setg(&invtsc_mig_blocker,
> >                     "State blocked by non-migratable CPU device"
> >                     " (invtsc flag)");
> > -        migrate_add_blocker(invtsc_mig_blocker);
> > +        r = migrate_add_blocker(invtsc_mig_blocker, NULL);
> > +        if (r < 0) {
> > +            error_report("kvm: migrate_add_blocker failed");
> > +            goto efail;
> > +        }
> >          /* for savevm */
> >          vmstate_x86_cpu.unmigratable = 1;
> >      }
> > @@ -969,12 +973,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >      cpuid_data.cpuid.padding = 0;
> >      r = kvm_vcpu_ioctl(cs, KVM_SET_CPUID2, &cpuid_data);
> >      if (r) {
> > -        return r;
> > +        goto fail;
> >      }
> >
> >      r = kvm_arch_set_tsc_khz(cs);
> >      if (r < 0) {
> > -        return r;
> > +        goto fail;
> >      }
> >
> >      /* vcpu's TSC frequency is either specified by user, or following
> > @@ -1001,6 +1005,12 @@ int kvm_arch_init_vcpu(CPUState *cs)
> >      }
> >
> >      return 0;
> > +
> > + fail:
> > +    migrate_del_blocker(invtsc_mig_blocker);
> > + efail:
> > +    error_free(invtsc_mig_blocker);
> > +    return r;
> >  }
> >
> >  void kvm_arch_reset_vcpu(X86CPU *cpu)
>
>
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[Qemu-devel] [PATCH v3 0/4] Introduce a new --only-migratable option, Ashijeet Acharya, 2017/01/04
- [Qemu-devel] [PATCH v3 1/4] migration: Add a new option to enable only-migratable, Ashijeet Acharya, 2017/01/04
- [Qemu-devel] [PATCH v3 2/4] migration: Allow "device add" options to only add migratable devices, Ashijeet Acharya, 2017/01/04
- [Qemu-devel] [PATCH v3 3/4] migration: disallow migrate_add_blocker during migration, Ashijeet Acharya, 2017/01/04
  - Re: [Qemu-devel] [PATCH v3 3/4] migration: disallow migrate_add_blocker during migration, Greg Kurz, 2017/01/06
    - Re: [Qemu-devel] [PATCH v2 3/4] migration: disallow migrate_add_blocker during migration, Ashijeet Acharya <=
    - Re: [Qemu-devel] [PATCH v2 3/4] migration: disallow migrate_add_blocker during migration, Greg Kurz, 2017/01/09
- [Qemu-devel] [PATCH v3 4/4] migration: Fail migration blocker for --only-migratble, Ashijeet Acharya, 2017/01/04
  - Re: [Qemu-devel] [PATCH v3 4/4] migration: Fail migration blocker for --only-migratble, Greg Kurz, 2017/01/06
    - [Qemu-devel] [PATCH v2 4/4] migration: Fail migration blocker for --only-migratble, Ashijeet Acharya, 2017/01/08
    - Re: [Qemu-devel] [PATCH v2 4/4] migration: Fail migration blocker for --only-migratble, Greg Kurz, 2017/01/09
    - Re: [Qemu-devel] [PATCH v2 4/4] migration: Fail migration blocker for --only-migratble, Ashijeet Acharya, 2017/01/09
- Re: [Qemu-devel] [PATCH v3 0/4] Introduce a new --only-migratable option, no-reply, 2017/01/04
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