[PATCH v3 3/9] block: Make it easier to learn which BDS support bitmaps

[Eric Blake]

Upcoming patches will enhance bitmap support in qemu-img, but in doing
so, it turns out to be nice to suppress output when bitmaps make no
sense (such as on a qcow2 v2 image).  Add a hook to make this easier
to query.

In the future, when we improve the ability to look up bitmaps through
a filter, we will probably also want to teach the block layer to
automatically let filters pass this request on through.

Signed-off-by: Eric Blake <address@hidden>
---
 block/qcow2.h                | 1 +
 include/block/block_int.h    | 1 +
 include/block/dirty-bitmap.h | 1 +
 block/dirty-bitmap.c         | 9 +++++++++
 block/qcow2-bitmap.c         | 7 +++++++
 block/qcow2.c                | 1 +
 6 files changed, 20 insertions(+)

diff --git a/block/qcow2.h b/block/qcow2.h
index f4de0a27d5c3..fb2b2b5a7b4d 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -764,6 +764,7 @@ bool qcow2_co_can_store_new_dirty_bitmap(BlockDriverState 
*bs,
 int qcow2_co_remove_persistent_dirty_bitmap(BlockDriverState *bs,
                                             const char *name,
                                             Error **errp);
+bool qcow2_dirty_bitmap_supported(BlockDriverState *bs);

 ssize_t coroutine_fn
 qcow2_co_compress(BlockDriverState *bs, void *dest, size_t dest_size,
diff --git a/include/block/block_int.h b/include/block/block_int.h
index df6d0273d679..cb1082da4c43 100644
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -560,6 +560,7 @@ struct BlockDriver {
                              uint64_t parent_perm, uint64_t parent_shared,
                              uint64_t *nperm, uint64_t *nshared);

+    bool (*bdrv_dirty_bitmap_supported)(BlockDriverState *bs);
     bool (*bdrv_co_can_store_new_dirty_bitmap)(BlockDriverState *bs,
                                                const char *name,
                                                uint32_t granularity,
diff --git a/include/block/dirty-bitmap.h b/include/block/dirty-bitmap.h
index 8a1002941892..6d2e1707639f 100644
--- a/include/block/dirty-bitmap.h
+++ b/include/block/dirty-bitmap.h
@@ -16,6 +16,7 @@ typedef enum BitmapCheckFlags {

 #define BDRV_BITMAP_MAX_NAME_SIZE 1023

+bool bdrv_dirty_bitmap_supported(BlockDriverState *bs);
 BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
                                           uint32_t granularity,
                                           const char *name,
diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 063793e31606..89869c483c44 100644
--- a/block/dirty-bitmap.c
+++ b/block/dirty-bitmap.c
@@ -478,6 +478,15 @@ int bdrv_remove_persistent_dirty_bitmap(BlockDriverState 
*bs, const char *name,
     }
 }

+bool
+bdrv_dirty_bitmap_supported(BlockDriverState *bs)
+{
+    if (bs->drv && bs->drv->bdrv_dirty_bitmap_supported) {
+        return bs->drv->bdrv_dirty_bitmap_supported(bs);
+    }
+    return false;
+}
+
 static bool coroutine_fn
 bdrv_co_can_store_new_dirty_bitmap(BlockDriverState *bs, const char *name,
                                    uint32_t granularity, Error **errp)
diff --git a/block/qcow2-bitmap.c b/block/qcow2-bitmap.c
index cb06954b4a5a..b9889c2144cd 100644
--- a/block/qcow2-bitmap.c
+++ b/block/qcow2-bitmap.c
@@ -1748,3 +1748,10 @@ fail:
                   name, bdrv_get_device_or_node_name(bs));
     return false;
 }
+
+bool qcow2_dirty_bitmap_supported(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+
+    return s->qcow_version >= 3;
+}
diff --git a/block/qcow2.c b/block/qcow2.c
index 1ad95ff04851..838d810ca5ec 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -5663,6 +5663,7 @@ BlockDriver bdrv_qcow2 = {
     .bdrv_detach_aio_context  = qcow2_detach_aio_context,
     .bdrv_attach_aio_context  = qcow2_attach_aio_context,

+    .bdrv_dirty_bitmap_supported = qcow2_dirty_bitmap_supported,
     .bdrv_co_can_store_new_dirty_bitmap = qcow2_co_can_store_new_dirty_bitmap,
     .bdrv_co_remove_persistent_dirty_bitmap =
             qcow2_co_remove_persistent_dirty_bitmap,
-- 
2.26.2