[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH v2 7/9] qcow2: Fix order of refcount updates in qcow
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH v2 7/9] qcow2: Fix order of refcount updates in qcow2_snapshot_goto |
Date: |
Fri, 18 Nov 2011 19:29:03 +0100 |
The refcount updates must be moved so that in the worst case we can get
cluster leaks, but refcounts may never be too low.
Signed-off-by: Kevin Wolf <address@hidden>
---
block/qcow2-refcount.c | 7 ++++-
block/qcow2-snapshot.c | 61 ++++++++++++++++++++++++++++++++++-------------
2 files changed, 50 insertions(+), 18 deletions(-)
diff --git a/block/qcow2-refcount.c b/block/qcow2-refcount.c
index 9605367..2db2ede 100644
--- a/block/qcow2-refcount.c
+++ b/block/qcow2-refcount.c
@@ -700,6 +700,10 @@ int qcow2_update_snapshot_refcount(BlockDriverState *bs,
l2_table = NULL;
l1_table = NULL;
l1_size2 = l1_size * sizeof(uint64_t);
+
+ /* WARNING: qcow2_snapshot_goto relies on this function not using the
+ * l1_table_offset when it is the current s->l1_table_offset! Be careful
+ * when changing this! */
if (l1_table_offset != s->l1_table_offset) {
if (l1_size2 != 0) {
l1_table = g_malloc0(align_offset(l1_size2, 512));
@@ -819,7 +823,8 @@ fail:
qcow2_cache_set_writethrough(bs, s->refcount_block_cache,
old_refcount_writethrough);
- if (l1_modified) {
+ /* Update L1 only if it isn't deleted anyway (addend = -1) */
+ if (addend >= 0 && l1_modified) {
for(i = 0; i < l1_size; i++)
cpu_to_be64s(&l1_table[i]);
if (bdrv_pwrite_sync(bs->file, l1_table_offset, l1_table,
diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
index 38b4ae3..20cb66e 100644
--- a/block/qcow2-snapshot.c
+++ b/block/qcow2-snapshot.c
@@ -387,6 +387,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char
*snapshot_id)
int i, snapshot_index;
int cur_l1_bytes, sn_l1_bytes;
int ret;
+ uint64_t *sn_l1_table = NULL;
/* Search the snapshot */
snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_id);
@@ -395,14 +396,6 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char
*snapshot_id)
}
sn = &s->snapshots[snapshot_index];
- /* Decrease refcount of clusters of current L1 table.
- * FIXME This is too early! */
- ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
- s->l1_size, -1);
- if (ret < 0) {
- goto fail;
- }
-
/*
* Make sure that the current L1 table is big enough to contain the whole
* L1 table of the snapshot. If the snapshot L1 table is smaller, the
@@ -416,33 +409,66 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char
*snapshot_id)
cur_l1_bytes = s->l1_size * sizeof(uint64_t);
sn_l1_bytes = sn->l1_size * sizeof(uint64_t);
- if (cur_l1_bytes > sn_l1_bytes) {
- memset(s->l1_table + sn->l1_size, 0, cur_l1_bytes - sn_l1_bytes);
- }
-
/*
* Copy the snapshot L1 table to the current L1 table.
*
* Before overwriting the old current L1 table on disk, make sure to
* increase all refcounts for the clusters referenced by the new one.
+ * Decrease the refcount referenced by the old one only when the L1
+ * table is overwritten.
*/
- ret = bdrv_pread(bs->file, sn->l1_table_offset, s->l1_table, sn_l1_bytes);
+ sn_l1_table = g_malloc0(cur_l1_bytes);
+
+ ret = bdrv_pread(bs->file, sn->l1_table_offset, sn_l1_table, sn_l1_bytes);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ ret = qcow2_update_snapshot_refcount(bs, sn->l1_table_offset,
+ sn->l1_size, 1);
if (ret < 0) {
goto fail;
}
- ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, s->l1_table,
+ ret = bdrv_pwrite_sync(bs->file, s->l1_table_offset, sn_l1_table,
cur_l1_bytes);
if (ret < 0) {
goto fail;
}
+ /*
+ * Decrease refcount of clusters of current L1 table.
+ *
+ * At this point, the in-memory s->l1_table points to the old L1 table,
+ * whereas on disk we already have the new one.
+ *
+ * qcow2_update_snapshot_refcount special cases the current L1 table to use
+ * the in-memory data instead of really using the offset to load a new one,
+ * which is why this works.
+ */
+ ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset,
+ s->l1_size, -1);
+
+ /*
+ * Now update the in-memory L1 table to be in sync with the on-disk one. We
+ * need to do this even if updating refcounts failed.
+ */
for(i = 0;i < s->l1_size; i++) {
- be64_to_cpus(&s->l1_table[i]);
+ s->l1_table[i] = be64_to_cpu(sn_l1_table[i]);
}
- /* FIXME This is too late! */
- ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size,
1);
+ if (ret < 0) {
+ goto fail;
+ }
+
+ g_free(sn_l1_table);
+ sn_l1_table = NULL;
+
+ /*
+ * Update QCOW_OFLAG_COPIED in the active L1 table (it may have changed
+ * when we decreased the refcount of the old snapshot.
+ */
+ ret = qcow2_update_snapshot_refcount(bs, s->l1_table_offset, s->l1_size,
0);
if (ret < 0) {
goto fail;
}
@@ -456,6 +482,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char
*snapshot_id)
return 0;
fail:
+ g_free(sn_l1_table);
return ret;
}
--
1.7.6.4
- [Qemu-devel] [PATCH v2 0/9] qcow2: Fix error paths for internal snapshots, Kevin Wolf, 2011/11/18
- [Qemu-devel] [PATCH v2 4/9] qcow2: Cleanups and memleak fix in qcow2_snapshot_create, Kevin Wolf, 2011/11/18
- [Qemu-devel] [PATCH v2 2/9] qcow2: Return real error code in qcow2_write_snapshots, Kevin Wolf, 2011/11/18
- [Qemu-devel] [PATCH v2 8/9] qcow2: Fix order in qcow2_snapshot_delete, Kevin Wolf, 2011/11/18
- [Qemu-devel] [PATCH v2 7/9] qcow2: Fix order of refcount updates in qcow2_snapshot_goto,
Kevin Wolf <=
- [Qemu-devel] [PATCH v2 9/9] qcow2: Fix error path in qcow2_snapshot_load_tmp, Kevin Wolf, 2011/11/18
- [Qemu-devel] [PATCH v2 6/9] qcow2: Return real error in qcow2_snapshot_goto, Kevin Wolf, 2011/11/18
- Re: [Qemu-devel] [PATCH v2 0/9] qcow2: Fix error paths for internal snapshots, Stefan Hajnoczi, 2011/11/21