cache_pos_advance
void cache_pos_advance(struct pcache_cache_pos *pos, u32 len);
cache_pos_advance(&key->cache_pos, cut_len);
cache_pos_advance(&cache->key_tail, get_kset_onmedia_size(kset_onmedia));
cache_pos_advance(&cache->key_head, sizeof(struct pcache_cache_kset_onmedia));
cache_pos_advance(&cache->key_head, kset_onmedia_size);
cache_pos_advance(pos, get_kset_onmedia_size(kset_onmedia));
cache_pos_advance(&pos, cache_key_lstart(key) - cache_key_lstart(key_tmp));
cache_pos_advance(&pos, cache_key_lstart(key) - cache_key_lstart(key_tmp));
cache_pos_advance(head_pos, to_alloc);
cache_pos_advance(head_pos, seg_remain);
cache_pos_advance(&cache->dirty_tail, cache->writeback_ctx.advance);