[Xen-changelog] [qemu-xen stable-4.10] migration, xen: Fix block image lock issue on live migration

[patchbot@xxxxxxx]

commit a4166a0a50dda967f30c9d85fa8aa2ea2539798e
Author:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
AuthorDate: Thu Nov 16 15:14:19 2017 +0000
Commit:     Anthony PERARD <anthony.perard@xxxxxxxxxx>
CommitDate: Mon Dec 18 12:24:12 2017 +0000

    migration, xen: Fix block image lock issue on live migration
    
    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>
    (cherry picked from commit 5d6c599fe1d69a1bf8c5c4d3c58be2b31cd625ad)
---
 migration/savevm.c | 23 ++++++++++++++++++++++-
 qapi-schema.json   |  6 +++++-
 2 files changed, 27 insertions(+), 2 deletions(-)

diff --git a/migration/savevm.c b/migration/savevm.c
index fdd15fa..ec8d03f 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -2197,13 +2197,20 @@ 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();
@@ -2218,6 +2225,20 @@ 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-schema.json b/qapi-schema.json
index 802ea53..bc6bc50 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -3271,6 +3271,9 @@
 # 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
@@ -3282,7 +3285,8 @@
 # <- { "return": {} }
 #
 ##
-{ 'command': 'xen-save-devices-state', 'data': {'filename': 'str'} }
+{ 'command': 'xen-save-devices-state',
+  'data': {'filename': 'str', '*live':'bool' } }
 
 ##
 # @xen-set-global-dirty-log:
--
generated by git-patchbot for /home/xen/git/qemu-xen.git#stable-4.10

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