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-rw-r--r--qemu/block-qcow2.c28
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,