qapi: nbd-export: allow select bitmaps by node/name pair

Hi all! Current logic of relying on search through backing chain is not
safe neither convenient.

Sometimes it leads to necessity of extra bitmap copying. Also, we are
going to add "snapshot-access" driver, to access some snapshot state
through NBD. And this driver is not formally a filter, and of course
it's not a COW format driver. So, searching through backing chain will
not work. Instead of widening the workaround of bitmap searching, let's
extend the interface so that user can select bitmap precisely.

Note, that checking for bitmap active status is not copied to the new
API, I don't see a reason for it, user should understand the risks. And
anyway, bitmap from other node is unrelated to this export being
read-only or read-write.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@openvz.org>
Message-Id: <20220314213226.362217-3-v.sementsov-og@mail.ru>
[eblake: Adjust S-o-b to Vladimir's new email, with permission]
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>

1 files changed, 41 insertions, 22 deletions

diff --git a/nbd/server.c b/nbd/server.c
index c5644fd3f6..4cdbc062c1 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -1643,7 +1643,7 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
     uint64_t perm, shared_perm;
     bool readonly = !exp_args->writable;
     bool shared = !exp_args->writable;
-    strList *bitmaps;
+    BlockDirtyBitmapOrStrList *bitmaps;
     size_t i;
     int ret;
 
@@ -1709,37 +1709,56 @@ static int nbd_export_create(BlockExport *blk_exp, BlockExportOptions *exp_args,
     }
     exp->export_bitmaps = g_new0(BdrvDirtyBitmap *, exp->nr_export_bitmaps);
     for (i = 0, bitmaps = arg->bitmaps; bitmaps;
-         i++, bitmaps = bitmaps->next) {
-        const char *bitmap = bitmaps->value;
+         i++, bitmaps = bitmaps->next)
+    {
+        const char *bitmap;
         BlockDriverState *bs = blk_bs(blk);
         BdrvDirtyBitmap *bm = NULL;
 
-        while (bs) {
-            bm = bdrv_find_dirty_bitmap(bs, bitmap);
-            if (bm != NULL) {
-                break;
+        switch (bitmaps->value->type) {
+        case QTYPE_QSTRING:
+            bitmap = bitmaps->value->u.local;
+            while (bs) {
+                bm = bdrv_find_dirty_bitmap(bs, bitmap);
+                if (bm != NULL) {
+                    break;
+                }
+
+                bs = bdrv_filter_or_cow_bs(bs);
             }
 
-            bs = bdrv_filter_or_cow_bs(bs);
-        }
+            if (bm == NULL) {
+                ret = -ENOENT;
+                error_setg(errp, "Bitmap '%s' is not found",
+                           bitmaps->value->u.local);
+                goto fail;
+            }
 
-        if (bm == NULL) {
-            ret = -ENOENT;
-            error_setg(errp, "Bitmap '%s' is not found", bitmap);
-            goto fail;
+            if (readonly && bdrv_is_writable(bs) &&
+                bdrv_dirty_bitmap_enabled(bm)) {
+                ret = -EINVAL;
+                error_setg(errp, "Enabled bitmap '%s' incompatible with "
+                           "readonly export", bitmap);
+                goto fail;
+            }
+            break;
+        case QTYPE_QDICT:
+            bitmap = bitmaps->value->u.external.name;
+            bm = block_dirty_bitmap_lookup(bitmaps->value->u.external.node,
+                                           bitmap, NULL, errp);
+            if (!bm) {
+                ret = -ENOENT;
+                goto fail;
+            }
+            break;
+        default:
+            abort();
         }
 
-        if (bdrv_dirty_bitmap_check(bm, BDRV_BITMAP_ALLOW_RO, errp)) {
-            ret = -EINVAL;
-            goto fail;
-        }
+        assert(bm);
 
-        if (readonly && bdrv_is_writable(bs) &&
-            bdrv_dirty_bitmap_enabled(bm)) {
+        if (bdrv_dirty_bitmap_check(bm, BDRV_BITMAP_ALLOW_RO, errp)) {
             ret = -EINVAL;
-            error_setg(errp,
-                       "Enabled bitmap '%s' incompatible with readonly export",
-                       bitmap);
             goto fail;
         }