[Qemu-devel] [PATCH] migration: introduce migrate_is_blocked()

[Greg Kurz <gkurz@linux.vnet.ibm.com>]

QEMU has currently two ways to prevent migration to occur:
- migration blocker when it depends on runtime state
- VMStateDescription.unmigratable when migration is not supported at all

This patch gathers all the logic into a single function to be called from
both the savevm and the migrate paths.

This fixes a bug with 9p, at least, where savevm would succeed and the
following would happen in the guest after loadvm:

$ ls /host
ls: cannot access /host: Protocol error

With this patch:

(qemu) savevm foo
Migration is disabled when VirtFS export path '/' is mounted in the guest
using mount_tag 'host'

Signed-off-by: Greg Kurz <gkurz@linux.vnet.ibm.com>
---

Since there has been some activity on 9p again since a few weeks, maybe it
is not too late for 2.6, if everybody agrees the fix is ok ?

 include/migration/migration.h |    1 +
 migration/migration.c         |   21 +++++++++++++++------
 migration/savevm.c            |    2 +-
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/include/migration/migration.h b/include/migration/migration.h
index ac2c12c2a518..9e36a97fc5e5 100644
--- a/include/migration/migration.h
+++ b/include/migration/migration.h
@@ -210,6 +210,7 @@ int migrate_fd_close(MigrationState *s);
 void add_migration_state_change_notifier(Notifier *notify);
 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_has_finished(MigrationState *);
 bool migration_has_failed(MigrationState *);
diff --git a/migration/migration.c b/migration/migration.c
index 991313a8629a..afd883b78179 100644
--- a/migration/migration.c
+++ b/migration/migration.c
@@ -992,6 +992,20 @@ void qmp_migrate_incoming(const char *uri, Error **errp)
     once = false;
 }
 
+bool migration_is_blocked(Error **errp)
+{
+    if (qemu_savevm_state_blocked(errp)) {
+        return true;
+    }
+
+    if (migration_blockers) {
+        *errp = error_copy(migration_blockers->data);
+        return true;
+    }
+
+    return false;
+}
+
 void qmp_migrate(const char *uri, bool has_blk, bool blk,
                  bool has_inc, bool inc, bool has_detach, bool detach,
                  Error **errp)
@@ -1014,12 +1028,7 @@ void qmp_migrate(const char *uri, bool has_blk, bool blk,
         return;
     }
 
-    if (qemu_savevm_state_blocked(errp)) {
-        return;
-    }
-
-    if (migration_blockers) {
-        *errp = error_copy(migration_blockers->data);
+    if (migration_is_blocked(errp)) {
         return;
     }
 
diff --git a/migration/savevm.c b/migration/savevm.c
index 16ba44379870..834664936dfc 100644
--- a/migration/savevm.c
+++ b/migration/savevm.c
@@ -1169,7 +1169,7 @@ static int qemu_savevm_state(QEMUFile *f, Error **errp)
     MigrationState *ms = migrate_init(&params);
     ms->to_dst_file = f;
 
-    if (qemu_savevm_state_blocked(errp)) {
+    if (migration_is_blocked(errp)) {
         return -EINVAL;
     }