block: allow migration to work with image files (v3)

Image files have two types of data: immutable data that describes things like
image size, backing files, etc. and mutable data that includes offset and
reference count tables.

Today, image formats aggressively cache mutable data to improve performance.  In
some cases, this happens before a guest even starts.  When dealing with live
migration, since a file is open on two machines, the caching of meta data can
lead to data corruption.

This patch addresses this by introducing a mechanism to invalidate any cached
mutable data a block driver may have which is then used by the live migration
code.

NB, this still requires coherent shared storage.  Addressing migration without
coherent shared storage (i.e. NFS) requires additional work.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

diff --git a/block.c b/block.c
index 86910b046c27e116adeb0c575a1319dc53dde276..d0158877d662c47598f0c8e55290a186d15a8945 100644 (file)
--- a/block.c
+++ b/block.c
@@ -2839,6 +2839,22 @@ int coroutine_fn bdrv_co_flush(BlockDriverState *bs)
     }
 }
 
+void bdrv_invalidate_cache(BlockDriverState *bs)
+{
+    if (bs->drv && bs->drv->bdrv_invalidate_cache) {
+        bs->drv->bdrv_invalidate_cache(bs);
+    }
+}
+
+void bdrv_invalidate_cache_all(void)
+{
+    BlockDriverState *bs;
+
+    QTAILQ_FOREACH(bs, &bdrv_states, list) {
+        bdrv_invalidate_cache(bs);
+    }
+}
+
 int bdrv_flush(BlockDriverState *bs)
 {
     Coroutine *co;

diff --git a/block.h b/block.h
index 051a25d8d63d141cc7c2ce5e3092dc1c6c7c7e3a..a826059897ef47cdcc4355cf77bf1f9f20d7dfaf 100644 (file)
--- a/block.h
+++ b/block.h
@@ -197,6 +197,10 @@ BlockDriverAIOCB *bdrv_aio_ioctl(BlockDriverState *bs,
         unsigned long int req, void *buf,
         BlockDriverCompletionFunc *cb, void *opaque);
 
+/* Invalidate any cached metadata used by image formats */
+void bdrv_invalidate_cache(BlockDriverState *bs);
+void bdrv_invalidate_cache_all(void);
+
 /* Ensure contents are flushed to disk.  */
 int bdrv_flush(BlockDriverState *bs);
 int coroutine_fn bdrv_co_flush(BlockDriverState *bs);

diff --git a/block_int.h b/block_int.h
index 1ec4921cc6f48e65fd4d8af6ebac2e10e5203fa3..77c0187c3d3ad287eb7f90385094acdd751a1c6f 100644 (file)
--- a/block_int.h
+++ b/block_int.h
@@ -87,6 +87,11 @@ struct BlockDriver {
     int coroutine_fn (*bdrv_co_discard)(BlockDriverState *bs,
         int64_t sector_num, int nb_sectors);
 
+    /*
+     * Invalidate any cached meta-data.
+     */
+    void (*bdrv_invalidate_cache)(BlockDriverState *bs);
+
     /*
      * Flushes all data that was already written to the OS all the way down to
      * the disk (for example raw-posix calls fsync()).

diff --git a/migration.c b/migration.c
index 6764d3a44cd9ea6b130c28c2a9b16479aaa52a2c..8280d7189aa4265d6b7204863d8d9d5c24d8820d 100644 (file)
--- a/migration.c
+++ b/migration.c
@@ -89,6 +89,9 @@ void process_incoming_migration(QEMUFile *f)
     qemu_announce_self();
     DPRINTF("successfully loaded vm state\n");
 
+    /* Make sure all file formats flush their mutable metadata */
+    bdrv_invalidate_cache_all();
+
     if (autostart) {
         vm_start();
     } else {