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Re: [Xen-devel] [PATCH] migration, xen: Fix block image lock issue on live migration



+ Stefano

On 11/27/2017 03:00 PM, Anthony PERARD wrote:
Hi Julien,

Hi Anthony,


Can I get a release-ack for this patch?

This fix local live migration of HVM guest when the disk backend is
qdisk.  osstest doesn't report a regression because the kernel or the
glibc is just a bit too old.

When does that regression happen? I am considering to release Xen 4.10 soon and would need more details to decide the inclusion of the patch.

Cheers,


Thanks,


On Wed, Nov 22, 2017 at 09:45:03AM +0100, Juan Quintela wrote:
From: Anthony PERARD <anthony.perard@xxxxxxxxxx>

When doing a live migration of a Xen guest with libxl, the images for
block devices are locked by the original QEMU process, and this prevent
the QEMU at the destination to take the lock and the migration fail.

>From QEMU point of view, once the RAM of a domain is migrated, there is
two QMP commands, "stop" then "xen-save-devices-state", at which point a
new QEMU is spawned at the destination.

Release locks in "xen-save-devices-state" so the destination can takes
them, if it's a live migration.

This patch add the "live" parameter to "xen-save-devices-state" which
default to true so older version of libxenlight can work with newer
version of QEMU.

Signed-off-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>
Reviewed-by: Dr. David Alan Gilbert <dgilbert@xxxxxxxxxx>
Reviewed-by: Juan Quintela <quintela@xxxxxxxxxx>
Signed-off-by: Juan Quintela <quintela@xxxxxxxxxx>
---
  migration/savevm.c  | 23 ++++++++++++++++++++++-
  qapi/migration.json |  6 +++++-
  2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index 192f2d82cd..b7908f62be 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2242,13 +2242,20 @@ int save_snapshot(const char *name, Error **errp)
      return ret;
  }
-void qmp_xen_save_devices_state(const char *filename, Error **errp)
+void qmp_xen_save_devices_state(const char *filename, bool has_live, bool live,
+                                Error **errp)
  {
      QEMUFile *f;
      QIOChannelFile *ioc;
      int saved_vm_running;
      int ret;
+ if (!has_live) {
+        /* live default to true so old version of Xen tool stack can have a
+         * successfull live migration */
+        live = true;
+    }
+
      saved_vm_running = runstate_is_running();
      vm_stop(RUN_STATE_SAVE_VM);
      global_state_store_running();
@@ -2263,6 +2270,20 @@ void qmp_xen_save_devices_state(const char *filename, 
Error **errp)
      qemu_fclose(f);
      if (ret < 0) {
          error_setg(errp, QERR_IO_ERROR);
+    } else {
+        /* libxl calls the QMP command "stop" before calling
+         * "xen-save-devices-state" and in case of migration failure, libxl
+         * would call "cont".
+         * So call bdrv_inactivate_all (release locks) here to let the other
+         * side of the migration take controle of the images.
+         */
+        if (live && !saved_vm_running) {
+            ret = bdrv_inactivate_all();
+            if (ret) {
+                error_setg(errp, "%s: bdrv_inactivate_all() failed (%d)",
+                           __func__, ret);
+            }
+        }
      }
the_end:
diff --git a/qapi/migration.json b/qapi/migration.json
index bbc4671ded..03f57c9616 100644
--- a/qapi/migration.json
+++ b/qapi/migration.json
@@ -1075,6 +1075,9 @@
  # data. See xen-save-devices-state.txt for a description of the binary
  # format.
  #
+# @live: Optional argument to ask QEMU to treat this command as part of a live
+# migration. Default to true. (since 2.11)
+#
  # Returns: Nothing on success
  #
  # Since: 1.1
@@ -1086,7 +1089,8 @@
  # <- { "return": {} }
  #
  ##
-{ 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
+{ 'command': 'xen-save-devices-state',
+  'data': {'filename': 'str', '*live':'bool' } }
##
  # @xen-set-replication:
--
2.13.6



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