block-backend: ignore inserted state in blk_co_nb_sectors

All callers of blk_co_nb_sectors (and blk_nb_sectors) are able to
handle a non-inserted CD-ROM as a zero-length file, they do not need
to raise an error.

Not using blk_co_is_available() aligns the function with
blk_co_get_geometry(), which becomes a simple wrapper for
blk_co_nb_sectors().  It will also make it possible to skip the creation
of a coroutine in the (common) case where bs->bl.has_variable_length
is false.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20230407153303.391121-8-pbonzini@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/block-backend.c

@@ -1615,33 +1615,26 @@ int64_t coroutine_fn blk_co_getlength(BlockBackend *blk)
     return bdrv_co_getlength(blk_bs(blk));
 }
 
-/* return 0 as number of sectors if no device present or error */
-void coroutine_fn blk_co_get_geometry(BlockBackend *blk,
-                                      uint64_t *nb_sectors_ptr)
+int64_t coroutine_fn blk_co_nb_sectors(BlockBackend *blk)
 {
     BlockDriverState *bs = blk_bs(blk);
 
     IO_CODE();
     GRAPH_RDLOCK_GUARD();
 
     if (!bs) {
-        *nb_sectors_ptr = 0;
+        return -ENOMEDIUM;
     } else {
-        int64_t nb_sectors = bdrv_co_nb_sectors(bs);
-        *nb_sectors_ptr = nb_sectors < 0 ? 0 : nb_sectors;
+        return bdrv_co_nb_sectors(bs);
     }
 }
 
-int64_t coroutine_fn blk_co_nb_sectors(BlockBackend *blk)
+/* return 0 as number of sectors if no device present or error */
+void coroutine_fn blk_co_get_geometry(BlockBackend *blk,
+                                      uint64_t *nb_sectors_ptr)
 {
-    IO_CODE();
-    GRAPH_RDLOCK_GUARD();
-
-    if (!blk_co_is_available(blk)) {
-        return -ENOMEDIUM;
-    }
-
-    return bdrv_co_nb_sectors(blk_bs(blk));
+    int64_t ret = blk_co_nb_sectors(blk);
+    *nb_sectors_ptr = ret < 0 ? 0 : ret;
 }
 
 BlockAIOCB *blk_aio_preadv(BlockBackend *blk, int64_t offset,