Refactor blockstore_init_meta into slightly more obvious code

src/blockstore_init.h

@@ -3,20 +3,29 @@
 
 #pragma once
 
+struct blockstore_init_meta_buf
+{
+    uint8_t *buf = NULL;
+    uint64_t size = 0;
+    uint64_t offset = 0;
+    int state = 0;
+};
+
 class blockstore_init_meta
 {
     blockstore_impl_t *bs;
     int wait_state = 0;
     bool zero_on_init = false;
     void *metadata_buffer = NULL;
-    uint64_t metadata_read = 0, md_offset = 0;
-    int prev = 0, prev_done = 0, done_len = 0, submitted = 0;
-    uint64_t done_cnt = 0, done_pos = 0;
-    uint64_t entries_loaded = 0;
+    blockstore_init_meta_buf bufs[2] = {};
+    int submitted = 0;
     struct io_uring_sqe *sqe;
     struct ring_data_t *data;
-    bool handle_entries(void *entries, unsigned count, int block_order);
-    void handle_event(ring_data_t *data);
+    uint64_t md_offset = 0;
+    uint64_t next_offset = 0;
+    uint64_t entries_loaded = 0;
+    bool handle_entries(uint8_t *buf, uint64_t count, uint64_t done_cnt);
+    void handle_event(ring_data_t *data, int buf_num);
 public:
     blockstore_init_meta(blockstore_impl_t *bs);
     int loop();