hw/9pfs: use migration blockers to prevent live migration when virtfs export path is mounted

Now when you try to migrate with VirtFS export path mounted, you get a proper QMP error:

(qemu) migrate tcp:localhost:4444
Migration is disabled when VirtFS export path '/tmp/' is mounted in the guest using mount_tag 'v_tmp'
(qemu)

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/hw/9pfs/virtio-9p.c b/hw/9pfs/virtio-9p.c
index 1b2fc5dfb6..32b98ddef2 100644
--- a/hw/9pfs/virtio-9p.c
+++ b/hw/9pfs/virtio-9p.c
@@ -23,6 +23,7 @@
 #include "virtio-9p-xattr.h"
 #include "virtio-9p-coth.h"
 #include "trace.h"
+#include "migration.h"
 
 int open_fd_hw;
 int total_open_fd;
@@ -373,6 +374,19 @@ static void put_fid(V9fsPDU *pdu, V9fsFidState *fidp)
      * Don't free the fid if it is in reclaim list
      */
     if (!fidp->ref && fidp->clunked) {
+        if (fidp->fid == pdu->s->root_fid) {
+            /*
+             * if the clunked fid is root fid then we
+             * have unmounted the fs on the client side.
+             * delete the migration blocker. Ideally, this
+             * should be hooked to transport close notification
+             */
+            if (pdu->s->migration_blocker) {
+                migrate_del_blocker(pdu->s->migration_blocker);
+                error_free(pdu->s->migration_blocker);
+                pdu->s->migration_blocker = NULL;
+            }
+        }
         free_fid(pdu, fidp);
     }
 }
@@ -1235,6 +1249,11 @@ static void v9fs_attach(void *opaque)
     err = offset;
     trace_v9fs_attach_return(pdu->tag, pdu->id,
                              qid.type, qid.version, qid.path);
+    s->root_fid = fid;
+    /* disable migration */
+    error_set(&s->migration_blocker, QERR_VIRTFS_FEATURE_BLOCKS_MIGRATION,
+              s->ctx.fs_root, s->tag);
+    migrate_add_blocker(s->migration_blocker);
 out:
     put_fid(pdu, fidp);
 out_nofid: