block: Make it easier to learn which BDS support bitmaps

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

This patch adds a new callback .bdrv_supports_persistent_dirty_bitmap,
rather than trying to shoehorn the answer in via existing callbacks.
In particular, while it might have been possible to overload
.bdrv_co_can_store_new_dirty_bitmap to special-case a NULL input to
answer whether any persistent bitmaps are supported, that is at odds
with whether a particular bitmap can be stored (for example, even on
an image that supports persistent bitmaps but has currently filled up
the maximum number of bitmaps, attempts to store another one should
fail); and the new functionality doesn't require coroutine safety.
Similarly, we could have added one more piece of information to
.bdrv_get_info, but then again, most callers to that function tend to
already discard extraneous information, and making it a catch-all
rather than a series of dedicated scalar queries hasn't really
simplified life.

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 <eblake@redhat.com>
Message-Id: <20200513011648.166876-4-eblake@redhat.com>
Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

diff --git a/block/dirty-bitmap.c b/block/dirty-bitmap.c
index 063793e3160675ca4ba1bf5b9344646654f4e9c8..f9bfc77985e86707d8287f9ea9c1547a1d1f7567 100644 (file)
--- 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_supports_persistent_dirty_bitmap(BlockDriverState *bs)
+{
+    if (bs->drv && bs->drv->bdrv_supports_persistent_dirty_bitmap) {
+        return bs->drv->bdrv_supports_persistent_dirty_bitmap(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 cb06954b4a5ab1881c5d5d6f4ec4e3636bb77913..1cf6d2ab77a3f4f3da87d9772aa445a98039ce94 100644 (file)
--- 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_supports_persistent_dirty_bitmap(BlockDriverState *bs)
+{
+    BDRVQcow2State *s = bs->opaque;
+
+    return s->qcow_version >= 3;
+}

diff --git a/block/qcow2.c b/block/qcow2.c
index fe0ce39799cc0d8a8399996be4f2f872c92f8d7a..dfab8d2f6cd85c3f4d363404b246fab4d608ed43 100644 (file)
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -5791,6 +5791,8 @@ BlockDriver bdrv_qcow2 = {
     .bdrv_detach_aio_context  = qcow2_detach_aio_context,
     .bdrv_attach_aio_context  = qcow2_attach_aio_context,
 
+    .bdrv_supports_persistent_dirty_bitmap =
+            qcow2_supports_persistent_dirty_bitmap,
     .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,

diff --git a/block/qcow2.h b/block/qcow2.h
index 6a8b82e6ccb118d157b07dd0c94a0653408c95a1..402e8acb1cb7dd691ad4a8781ec7c301a5dcad71 100644 (file)
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -782,6 +782,7 @@ 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_supports_persistent_dirty_bitmap(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 5e4f4c348cf1de8e21418b8bb1d0faa945ee924f..33a12916f427eb4bfa7b458e80420bb7e8a99408 100644 (file)
--- a/include/block/block_int.h
+++ b/include/block/block_int.h
@@ -568,6 +568,7 @@ struct BlockDriver {
                              uint64_t parent_perm, uint64_t parent_shared,
                              uint64_t *nperm, uint64_t *nshared);
 
+    bool (*bdrv_supports_persistent_dirty_bitmap)(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 8a1002941892263903f5cabec294c51eab0c65c2..5a8d52e4deafbb9706b3bfc05fc8724651e196ed 100644 (file)
--- 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_supports_persistent_dirty_bitmap(BlockDriverState *bs);
 BdrvDirtyBitmap *bdrv_create_dirty_bitmap(BlockDriverState *bs,
                                           uint32_t granularity,
                                           const char *name,