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kvm tools, qcow: Delayed L2 table writeout

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This patch delays writeout for new L2 tables like we do for L1 tables. If a L2
table has non-allocated clusters, we mark that in the in-memory L2 table but
don't actually write it to disk until the L2 table is thrown out of LRU cache
or when qcow_disk_flush() is called. That makes writes to new clusters volatile
before VIRTIO_BLK_T_FLUSH is issued without corrupting the QCOW image on I/O
error.

Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@gmail.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Prasad Joshi <prasadjoshi124@gmail.com>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
This commit is contained in:
Pekka Enberg
2011-07-09 10:58:37 +03:00
committed by Will Deacon
parent 4bd7e48bc8
commit a4e46515fd
1 changed files with 39 additions and 27 deletions
Download Patch File Download Diff File Expand all files Collapse all files
disk/qcow.c
+39 -27
View File
@@ -88,6 +88,16 @@ static void free_cache(struct qcow *q)
}
}
static int qcow_l2_cache_write(struct qcow *q, struct qcow_l2_table *c)
{
struct qcow_header *header = q->header;
u64 size;
size = 1 << header->l2_bits;
return pwrite_in_full(q->fd, c->table, size * sizeof(u64), c->offset);
}
static int cache_table(struct qcow *q, struct qcow_l2_table *c)
{
struct rb_root *r = &q->root;
@@ -100,6 +110,9 @@ static int cache_table(struct qcow *q, struct qcow_l2_table *c)
*/
lru = list_first_entry(&q->lru_list, struct qcow_l2_table, list);
if (qcow_l2_cache_write(q, lru) < 0)
goto error;
/* Remove the node from the cache */
rb_erase(&lru->node, r);
list_del_init(&lru->list);
@@ -361,7 +374,6 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
struct qcow_header *header = q->header;
struct qcow_table *table = &q->table;
struct qcow_l2_table *l2t;
bool update_meta;
u64 clust_start;
u64 clust_off;
u64 clust_sz;
@@ -371,7 +383,6 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
u64 l2t_sz;
u64 f_sz;
u64 len;
u64 t;
l2t = NULL;
l2t_sz = 1 << header->l2_bits;
@@ -434,31 +445,16 @@ static ssize_t qcow_write_cluster(struct qcow *q, u64 offset, void *buf, u32 src
clust_start = be64_to_cpu(l2t->table[l2t_idx]) & ~header->oflag_mask;
if (!clust_start) {
clust_start = ALIGN(f_sz, clust_sz);
update_meta = true;
} else
update_meta = false;
/* Write actual data */
if (pwrite_in_full(q->fd, buf, len, clust_start + clust_off) < 0)
goto error;
if (update_meta) {
t = cpu_to_be64(clust_start);
if (qcow_pwrite_sync(q->fd, &t, sizeof(t), l2t_off + l2t_idx * sizeof(u64)) < 0) {
/* Restore the file to consistent state */
if (ftruncate(q->fd, f_sz) < 0)
goto error;
goto error;
}
/* Update the cached level2 entry */
l2t->table[l2t_idx] = cpu_to_be64(clust_start);
clust_start = ALIGN(f_sz, clust_sz);
l2t->table[l2t_idx] = cpu_to_be64(clust_start);
}
mutex_unlock(&q->mutex);
/* Write actual data */
if (pwrite_in_full(q->fd, buf, len, clust_start + clust_off) < 0)
return -1;
return len;
free_cache:
@@ -508,18 +504,34 @@ static int qcow_disk_flush(struct disk_image *disk)
{
struct qcow *q = disk->priv;
struct qcow_header *header;
struct list_head *pos, *n;
struct qcow_table *table;
if (fdatasync(disk->fd) < 0)
return -1;
header = q->header;
table = &q->table;
mutex_lock(&q->mutex);
list_for_each_safe(pos, n, &q->lru_list) {
struct qcow_l2_table *c = list_entry(pos, struct qcow_l2_table, list);
if (qcow_l2_cache_write(q, c) < 0)
goto error_unlock;
}
if (fdatasync(disk->fd) < 0)
goto error_unlock;
if (pwrite_in_full(disk->fd, table->l1_table, table->table_size * sizeof(u64), header->l1_table_offset) < 0)
return -1;
goto error_unlock;
mutex_unlock(&q->mutex);
return fsync(disk->fd);
error_unlock:
mutex_unlock(&q->mutex);
return -1;
}
static int qcow_disk_close(struct disk_image *disk)