[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
[Qemu-devel] [PATCH v2] qcow2: Set zero flag for discarded clusters
From: |
Kevin Wolf |
Subject: |
[Qemu-devel] [PATCH v2] qcow2: Set zero flag for discarded clusters |
Date: |
Mon, 17 Feb 2014 15:45:47 +0100 |
Instead of making the backing file contents visible again after a discard
request, set the zero flag if possible (i.e. on version >= 3).
Signed-off-by: Kevin Wolf <address@hidden>
---
block/qcow2-cluster.c | 22 ++++++++++++++++++++--
tests/qemu-iotests/046 | 18 ++++++++++++++----
2 files changed, 34 insertions(+), 6 deletions(-)
diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
index cd2dcfa..f404ef1 100644
--- a/block/qcow2-cluster.c
+++ b/block/qcow2-cluster.c
@@ -1332,13 +1332,31 @@ static int discard_single_l2(BlockDriverState *bs,
uint64_t offset,
uint64_t old_offset;
old_offset = be64_to_cpu(l2_table[l2_index + i]);
- if ((old_offset & L2E_OFFSET_MASK) == 0) {
+
+ /*
+ * Make sure that a discarded area reads back as zeroes for v3 images
+ * (we cannot do it for v2 without actually writing a zero-filled
+ * buffer). We can skip the operation if the cluster is already marked
+ * as zero, or if it's unallocated and we don't have a backing file.
+ *
+ * TODO We might want to use bdrv_get_block_status(bs) here, but we're
+ * holding s->lock, so that doesn't work today.
+ */
+ if (!!(old_offset & QCOW_OFLAG_ZERO)) {
+ continue;
+ }
+
+ if ((old_offset & L2E_OFFSET_MASK) == 0 && !bs->backing_hd) {
continue;
}
/* First remove L2 entries */
qcow2_cache_entry_mark_dirty(s->l2_table_cache, l2_table);
- l2_table[l2_index + i] = cpu_to_be64(0);
+ if (s->qcow_version >= 3) {
+ l2_table[l2_index + i] = cpu_to_be64(QCOW_OFLAG_ZERO);
+ } else {
+ l2_table[l2_index + i] = cpu_to_be64(0);
+ }
/* Then decrease the refcount */
qcow2_free_any_clusters(bs, old_offset, 1, type);
diff --git a/tests/qemu-iotests/046 b/tests/qemu-iotests/046
index 2d44bbb..e0be46c 100755
--- a/tests/qemu-iotests/046
+++ b/tests/qemu-iotests/046
@@ -193,6 +193,16 @@ echo "== Verify image content =="
function verify_io()
{
+ if ($QEMU_IMG info -f "$IMGFMT" "$TEST_IMG" | grep "compat: 0.10" >
/dev/null); then
+ # For v2 images, discarded clusters are read from the backing file
+ # Keep the variable empty so that the backing file value can be used as
+ # the default below
+ discarded=
+ else
+ # Discarded clusters are zeroed for v3 or later
+ discarded=0
+ fi
+
echo read -P 0 0 0x10000
echo read -P 1 0x10000 0x2000
@@ -221,16 +231,16 @@ function verify_io()
echo read -P 70 0x78000 0x6000
echo read -P 7 0x7e000 0x2000
- echo read -P 8 0x80000 0x6000
+ echo read -P ${discarded:-8} 0x80000 0x6000
echo read -P 80 0x86000 0x2000
- echo read -P 8 0x88000 0x2000
+ echo read -P ${discarded:-8} 0x88000 0x2000
echo read -P 81 0x8a000 0xe000
echo read -P 90 0x98000 0x6000
echo read -P 9 0x9e000 0x2000
- echo read -P 10 0xa0000 0x6000
+ echo read -P ${discarded:-10} 0xa0000 0x6000
echo read -P 100 0xa6000 0x2000
- echo read -P 10 0xa8000 0x2000
+ echo read -P ${discarded:-10} 0xa8000 0x2000
echo read -P 101 0xaa000 0xe000
echo read -P 110 0xb8000 0x8000
--
1.8.1.4
- [Qemu-devel] [PATCH v2] qcow2: Set zero flag for discarded clusters,
Kevin Wolf <=