block/backup-top: drop .active

We don't need this workaround anymore: bdrv_append is already smart
enough and we can use new bdrv_drop_filter().

This commit efficiently reverts also recent 705dde27c6, which
checked .active on io path. Still it said that the problem should be
theoretical. And the logic of filter removement is changed anyway.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-Id: <20210428151804.439460-25-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/backup-top.c

@@ -37,7 +37,6 @@
 typedef struct BDRVBackupTopState {
     BlockCopyState *bcs;
     BdrvChild *target;
-    bool active;
     int64_t cluster_size;
 } BDRVBackupTopState;
 
@@ -45,12 +44,6 @@ static coroutine_fn int backup_top_co_preadv(
         BlockDriverState *bs, uint64_t offset, uint64_t bytes,
         QEMUIOVector *qiov, int flags)
 {
-    BDRVBackupTopState *s = bs->opaque;
-
-    if (!s->active) {
-        return -EIO;
-    }
-
     return bdrv_co_preadv(bs->backing, offset, bytes, qiov, flags);
 }
 
@@ -60,10 +53,6 @@ static coroutine_fn int backup_top_cbw(BlockDriverState *bs, uint64_t offset,
     BDRVBackupTopState *s = bs->opaque;
     uint64_t off, end;
 
-    if (!s->active) {
-        return -EIO;
-    }
-
     if (flags & BDRV_REQ_WRITE_UNCHANGED) {
         return 0;
     }
@@ -137,21 +126,6 @@ static void backup_top_child_perm(BlockDriverState *bs, BdrvChild *c,
                                   uint64_t perm, uint64_t shared,
                                   uint64_t *nperm, uint64_t *nshared)
 {
-    BDRVBackupTopState *s = bs->opaque;
-
-    if (!s->active) {
-        /*
-         * The filter node may be in process of bdrv_append(), which firstly do
-         * bdrv_set_backing_hd() and then bdrv_replace_node(). This means that
-         * we can't unshare BLK_PERM_WRITE during bdrv_append() operation. So,
-         * let's require nothing during bdrv_append() and refresh permissions
-         * after it (see bdrv_backup_top_append()).
-         */
-        *nperm = 0;
-        *nshared = BLK_PERM_ALL;
-        return;
-    }
-
     if (!(role & BDRV_CHILD_FILTERED)) {
         /*
          * Target child
@@ -241,17 +215,6 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
     }
     appended = true;
 
-    /*
-     * bdrv_append() finished successfully, now we can require permissions
-     * we want.
-     */
-    state->active = true;
-    ret = bdrv_child_refresh_perms(top, top->backing, errp);
-    if (ret < 0) {
-        error_prepend(errp, "Cannot set permissions for backup-top filter: ");
-        goto fail;
-    }
-
     state->cluster_size = cluster_size;
     state->bcs = block_copy_state_new(top->backing, state->target,
                                       cluster_size, perf->use_copy_range,
@@ -268,7 +231,6 @@ BlockDriverState *bdrv_backup_top_append(BlockDriverState *source,
 
 fail:
     if (appended) {
-        state->active = false;
         bdrv_backup_top_drop(top);
     } else {
         bdrv_unref(top);
@@ -283,16 +245,9 @@ void bdrv_backup_top_drop(BlockDriverState *bs)
 {
     BDRVBackupTopState *s = bs->opaque;
 
-    bdrv_drained_begin(bs);
+    bdrv_drop_filter(bs, &error_abort);
 
     block_copy_state_free(s->bcs);
 
-    s->active = false;
-    bdrv_child_refresh_perms(bs, bs->backing, &error_abort);
-    bdrv_replace_node(bs, bs->backing->bs, &error_abort);
-    bdrv_set_backing_hd(bs, NULL, &error_abort);
-
-    bdrv_drained_end(bs);
-
     bdrv_unref(bs);
 }

tests/qemu-iotests/283.out

@@ -5,7 +5,7 @@
 {"execute": "blockdev-add", "arguments": {"driver": "blkdebug", "image": "base", "node-name": "other", "take-child-perms": ["write"]}}
 {"return": {}}
 {"execute": "blockdev-backup", "arguments": {"device": "source", "sync": "full", "target": "target"}}
-{"error": {"class": "GenericError", "desc": "Cannot set permissions for backup-top filter: Conflicts with use by source as 'image', which does not allow 'write' on base"}}
+{"error": {"class": "GenericError", "desc": "Cannot append backup-top filter: Conflicts with use by source as 'image', which does not allow 'write' on base"}}
 
 === backup-top should be gone after job-finalize ===