int qcow2_alloc_cluster_link_l2(BlockDriverState *bs, QCowL2Meta *m) { BDRVQcowState *s = bs->opaque; int i, j = 0, l2_index, ret; uint64_t *old_cluster, *l2_table; uint64_t cluster_offset = m->alloc_offset; trace_qcow2_cluster_link_l2(qemu_coroutine_self(), m->nb_clusters); assert(m->nb_clusters > 0); old_cluster = g_malloc(m->nb_clusters * sizeof(uint64_t)); /* copy content of unmodified sectors */ ret = perform_cow(bs, m, &m->cow_start); if (ret < 0) { goto err; } ret = perform_cow(bs, m, &m->cow_end); if (ret < 0) { goto err; } /* Update L2 table. */ if (s->use_lazy_refcounts) { qcow2_mark_dirty(bs); } if (qcow2_need_accurate_refcounts(s)) { qcow2_cache_set_dependency(bs, s->l2_table_cache, s->refcount_block_cache); } ret = get_cluster_table(bs, m->offset, &l2_table, &l2_index); if (ret < 0) { goto err; } qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table); for (i = 0; i < m->nb_clusters; i++) { /* if two concurrent writes happen to the same unallocated cluster * each write allocates separate cluster and writes data concurrently. * The first one to complete updates l2 table with pointer to its * cluster the second one has to do RMW (which is done above by * copy_sectors()), update l2 table with its cluster pointer and free * old cluster. This is what this loop does */ if(l2_table[l2_index + i] != 0) old_cluster[j++] = l2_table[l2_index + i]; l2_table[l2_index + i] = cpu_to_be64((cluster_offset + (i << s->cluster_bits)) | QCOW_OFLAG_COPIED); } ret = qcow2_cache_put(bs, s->l2_table_cache, (void**) &l2_table); if (ret < 0) { goto err; } /* * If this was a COW, we need to decrease the refcount of the old cluster. * Also flush bs->file to get the right order for L2 and refcount update. * * Don't discard clusters that reach a refcount of 0 (e.g. compressed * clusters), the next write will reuse them anyway. */ if (j != 0) { for (i = 0; i < j; i++) { qcow2_free_any_clusters(bs, be64_to_cpu(old_cluster[i]), 1, QCOW2_DISCARD_NEVER); } } ret = 0; err: g_free(old_cluster); return ret; }