diff options
| -rw-r--r-- | qemu/block-qcow2.c | 28 |
1 files changed, 25 insertions, 3 deletions
diff --git a/qemu/block-qcow2.c b/qemu/block-qcow2.c index 9c8212bf..50561f15 100644 --- a/qemu/block-qcow2.c +++ b/qemu/block-qcow2.c @@ -1005,6 +1005,28 @@ typedef struct QCowL2Meta int nb_clusters; } QCowL2Meta; +/* + * Write L2 table updates to disk, writing whole sectors to avoid a + * read-modify-write in bdrv_pwrite + */ +#define L2_ENTRIES_PER_SECTOR (512 / 8) +static int write_l2_entries(BDRVQcowState *s, uint64_t *l2_table, + uint64_t l2_offset, int l2_index, int num) +{ + int l2_start_index = l2_index & ~(L1_ENTRIES_PER_SECTOR - 1); + int start_offset = (8 * l2_index) & ~511; + int end_offset = (8 * (l2_index + num) + 511) & ~511; + size_t len = end_offset - start_offset; + + if (bdrv_pwrite(s->hd, l2_offset + start_offset, &l2_table[l2_start_index], + len) != len) + { + return -1; + } + + return 0; +} + static int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset, QCowL2Meta *m) { @@ -1053,10 +1075,10 @@ static int alloc_cluster_link_l2(BlockDriverState *bs, uint64_t cluster_offset, (i << s->cluster_bits)) | QCOW_OFLAG_COPIED); } - if (bdrv_pwrite(s->hd, l2_offset + l2_index * sizeof(uint64_t), - l2_table + l2_index, m->nb_clusters * sizeof(uint64_t)) != - m->nb_clusters * sizeof(uint64_t)) + if (write_l2_entries(s, l2_table, l2_offset, l2_index, m->nb_clusters) < 0) { + ret = -1; goto err; + } for (i = 0; i < j; i++) free_any_clusters(bs, be64_to_cpu(old_cluster[i]) & ~QCOW_OFLAG_COPIED, |