block/io: introduce block driver snapshot-access API

Add new block driver handlers and corresponding generic wrappers.
It will be used to allow copy-before-write filter to provide
reach fleecing interface in further commit.

In future this approach may be used to allow reading qcow2 internal
snapshots, for example to export them through NBD.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Hanna Reitz <hreitz@redhat.com>
Message-Id: <20220303194349.2304213-11-vsementsov@virtuozzo.com>
[hreitz: Rebased on block GS/IO split]
Signed-off-by: Hanna Reitz <hreitz@redhat.com>

1 files changed, 72 insertions, 0 deletions

diff --git a/block/io.c b/block/io.c
index 8bee484463..f0c8da6b9f 100644
--- a/block/io.c
+++ b/block/io.c
@@ -3654,3 +3654,75 @@ void bdrv_cancel_in_flight(BlockDriverState *bs)
         bs->drv->bdrv_cancel_in_flight(bs);
     }
 }
+
+int coroutine_fn
+bdrv_co_preadv_snapshot(BdrvChild *child, int64_t offset, int64_t bytes,
+                        QEMUIOVector *qiov, size_t qiov_offset)
+{
+    BlockDriverState *bs = child->bs;
+    BlockDriver *drv = bs->drv;
+    int ret;
+    IO_CODE();
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
+    if (!drv->bdrv_co_preadv_snapshot) {
+        return -ENOTSUP;
+    }
+
+    bdrv_inc_in_flight(bs);
+    ret = drv->bdrv_co_preadv_snapshot(bs, offset, bytes, qiov, qiov_offset);
+    bdrv_dec_in_flight(bs);
+
+    return ret;
+}
+
+int coroutine_fn
+bdrv_co_snapshot_block_status(BlockDriverState *bs,
+                              bool want_zero, int64_t offset, int64_t bytes,
+                              int64_t *pnum, int64_t *map,
+                              BlockDriverState **file)
+{
+    BlockDriver *drv = bs->drv;
+    int ret;
+    IO_CODE();
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
+    if (!drv->bdrv_co_snapshot_block_status) {
+        return -ENOTSUP;
+    }
+
+    bdrv_inc_in_flight(bs);
+    ret = drv->bdrv_co_snapshot_block_status(bs, want_zero, offset, bytes,
+                                             pnum, map, file);
+    bdrv_dec_in_flight(bs);
+
+    return ret;
+}
+
+int coroutine_fn
+bdrv_co_pdiscard_snapshot(BlockDriverState *bs, int64_t offset, int64_t bytes)
+{
+    BlockDriver *drv = bs->drv;
+    int ret;
+    IO_CODE();
+
+    if (!drv) {
+        return -ENOMEDIUM;
+    }
+
+    if (!drv->bdrv_co_pdiscard_snapshot) {
+        return -ENOTSUP;
+    }
+
+    bdrv_inc_in_flight(bs);
+    ret = drv->bdrv_co_pdiscard_snapshot(bs, offset, bytes);
+    bdrv_dec_in_flight(bs);
+
+    return ret;
+}