[Qemu-devel] [RFC PATCH 06/16] block: Introduce bdrv_dirty_bitmap_set_persistent

[Fam Zheng <famz@redhat.com>]

By implementing bdrv_dirty_bitmap_set_persistent, a driver can support
the persistent dirty bitmap feature.

Once a dirty bitmap is made persistent, the driver is responsible for saving
the dirty bitmap when appropriate, for example before close; if a persistent
bitmap is removed or made non-persistent, .bdrv_dirty_bitmap_set_persistent
will be called, the driver should then remove the dirty bitmap from the disk.

This operation is not recursed in block layer, a filter such as blkdebug needs
to implement the callback and explicitly pass down to bs->file, etc.

Signed-off-by: Fam Zheng <famz@redhat.com>
---
 block/dirty-bitmap.c         | 38 ++++++++++++++++++++++++++++++++++++++
 include/block/block_int.h    |  8 ++++++++
 include/block/dirty-bitmap.h |  4 ++++
 3 files changed, 50 insertions(+)

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 1aa7f76..882a0db 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -43,6 +43,7 @@ struct BdrvDirtyBitmap {
     int64_t size;               /* Size of the bitmap (Number of sectors) */
     bool disabled;              /* Bitmap is read-only */
     int active_iterators;       /* How many iterators are active */
+    bool persistent;            /* Whether this bitmap is persistent. */
     QLIST_ENTRY(BdrvDirtyBitmap) list;
 };
 
@@ -71,6 +72,37 @@ void bdrv_dirty_bitmap_make_anon(BdrvDirtyBitmap *bitmap)
     bitmap->name = NULL;
 }
 
+int bdrv_dirty_bitmap_set_persistent(BlockDriverState *bs,
+                                     BdrvDirtyBitmap *bitmap,
+                                     bool persistent, bool flag_only,
+                                     Error **errp)
+{
+    int ret = 0;
+
+    if (!bitmap->name) {
+        error_setg(errp, "Cannot change the persistent status of an anonymous"
+                         "bitmap");
+        return -EINVAL;
+    }
+
+    if (persistent == bitmap->persistent) {
+        return 0;
+    }
+
+    if (!flag_only) {
+        if (!bs->drv || !bs->drv->bdrv_dirty_bitmap_set_persistent) {
+            error_setg(errp, "Not supported in this format.");
+            return -ENOTSUP;
+        }
+        ret = bs->drv->bdrv_dirty_bitmap_set_persistent(bs, bitmap, persistent,
+                                                        errp);
+    }
+    if (!ret) {
+        bitmap->persistent = persistent;
+    }
+    return ret;
+}
+
 BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
                                           uint32_t granularity,
                                           const char *name,
@@ -194,6 +226,12 @@ int bdrv_dirty_bitmap_create_successor(BlockDriverState *bs,
     uint64_t granularity;
     BdrvDirtyBitmap *child;
 
+    if (bitmap->persistent) {
+        error_setg(errp, "Cannot create a successor for a bitmap that is "
+                   "persistent");
+        return -1;
+    }
+
     if (bdrv_dirty_bitmap_frozen(bitmap)) {
         error_setg(errp, "Cannot create a successor for a bitmap that is "
                    "currently frozen");
diff --git a/include/block/block_int.h b/include/block/block_int.h
index 5fa58e8..fbc34af 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -305,6 +305,14 @@ struct BlockDriver {
      */
     void (*bdrv_drain)(BlockDriverState *bs);
 
+    /**
+     * Make the dirty bitmap persistent if persistent=true or transient
+     * otherwise.
+     */
+    int (*bdrv_dirty_bitmap_set_persistent)(BlockDriverState *bs,
+                                            BdrvDirtyBitmap *bitmap,
+                                            bool persistent, Error **errp);
+
     QLIST_ENTRY(BlockDriver) list;
 };
 
diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
index d14d923..5885720 100644
--- a/include/block/dirty-bitmap.h
+++ b/include/block/dirty-bitmap.h
@@ -24,6 +24,10 @@ BdrvDirtyBitmap *bdrv_reclaim_dirty_bitmap(BlockDriverState *bs,
 BdrvDirtyBitmap *bdrv_find_dirty_bitmap(BlockDriverState *bs,
                                         const char *name);
 void bdrv_dirty_bitmap_make_anon(BdrvDirtyBitmap *bitmap);
+int bdrv_dirty_bitmap_set_persistent(BlockDriverState *bs,
+                                     BdrvDirtyBitmap *bitmap,
+                                     bool persistent, bool flag_only,
+                                     Error **errp);
 void bdrv_release_dirty_bitmap(BlockDriverState *bs, BdrvDirtyBitmap *bitmap);
 void bdrv_disable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
 void bdrv_enable_dirty_bitmap(BdrvDirtyBitmap *bitmap);
-- 
2.4.3