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[Qemu-devel] [PATCH v2] qcow2: Implement bdrv_truncate() for growing ima
From: |
Stefan Hajnoczi |
Subject: |
[Qemu-devel] [PATCH v2] qcow2: Implement bdrv_truncate() for growing images |
Date: |
Wed, 28 Apr 2010 10:24:15 +0100 |
This patch adds the ability to grow qcow2 images in-place using
bdrv_truncate(). This enables qemu-img resize command support for
qcow2.
Snapshots are not supported and bdrv_truncate() will return -ENOTSUP.
The notion of resizing an image with snapshots could lead to confusion:
users may expect snapshots to remain unchanged, but this is not possible
with the current qcow2 on-disk format where the header.size field is
global instead of per-snapshot. Others may expect snapshots to change
size along with the current image data. I think it is safest to not
support snapshots and perhaps add behavior later if there is a
consensus.
Backing images continue to work. If the image is now larger than its
backing image, zeroes are read when accessing beyond the end of the
backing image.
Signed-off-by: Stefan Hajnoczi <address@hidden>
---
v2:
* Remove superfluous qcow2_grow_l1_table()-related changes
block/qcow2.c | 45 +++++++++++++++++++++++++++++++++++++++++----
block/qcow2.h | 6 ++++++
2 files changed, 47 insertions(+), 4 deletions(-)
diff --git a/block/qcow2.c b/block/qcow2.c
index 4fa3ff9..a65af41 100644
--- a/block/qcow2.c
+++ b/block/qcow2.c
@@ -140,7 +140,7 @@ static int qcow_read_extensions(BlockDriverState *bs,
uint64_t start_offset,
static int qcow_open(BlockDriverState *bs, int flags)
{
BDRVQcowState *s = bs->opaque;
- int len, i, shift;
+ int len, i;
QCowHeader header;
uint64_t ext_end;
@@ -188,8 +188,7 @@ static int qcow_open(BlockDriverState *bs, int flags)
/* read the level 1 table */
s->l1_size = header.l1_size;
- shift = s->cluster_bits + s->l2_bits;
- s->l1_vm_state_index = (header.size + (1LL << shift) - 1) >> shift;
+ s->l1_vm_state_index = size_to_l1(s, header.size);
/* the L1 table must contain at least enough entries to put
header.size bytes */
if (s->l1_size < s->l1_vm_state_index)
@@ -851,6 +850,42 @@ static int qcow_make_empty(BlockDriverState *bs)
return 0;
}
+static int qcow2_truncate(BlockDriverState *bs, int64_t offset)
+{
+ BDRVQcowState *s = bs->opaque;
+ int ret, new_l1_size;
+
+ if (offset & 511) {
+ return -EINVAL;
+ }
+
+ /* cannot proceed if image has snapshots */
+ if (s->nb_snapshots) {
+ return -ENOTSUP;
+ }
+
+ /* shrinking is currently not supported */
+ if (offset < bs->total_sectors * 512) {
+ return -ENOTSUP;
+ }
+
+ new_l1_size = size_to_l1(s, offset);
+ ret = qcow2_grow_l1_table(bs, new_l1_size);
+ if (ret < 0) {
+ return ret;
+ }
+
+ /* write updated header.size */
+ offset = cpu_to_be64(offset);
+ if (bdrv_pwrite(bs->file, offsetof(QCowHeader, size), &offset,
+ sizeof(uint64_t)) != sizeof(uint64_t)) {
+ return -EIO;
+ }
+
+ s->l1_vm_state_index = new_l1_size;
+ return 0;
+}
+
/* XXX: put compressed sectors first, then all the cluster aligned
tables to avoid losing bytes in alignment */
static int qcow_write_compressed(BlockDriverState *bs, int64_t sector_num,
@@ -1050,7 +1085,9 @@ static BlockDriver bdrv_qcow2 = {
.bdrv_aio_readv = qcow_aio_readv,
.bdrv_aio_writev = qcow_aio_writev,
.bdrv_aio_flush = qcow_aio_flush,
- .bdrv_write_compressed = qcow_write_compressed,
+
+ .bdrv_truncate = qcow2_truncate,
+ .bdrv_write_compressed = qcow_write_compressed,
.bdrv_snapshot_create = qcow2_snapshot_create,
.bdrv_snapshot_goto = qcow2_snapshot_goto,
diff --git a/block/qcow2.h b/block/qcow2.h
index 5bd08db..01053b7 100644
--- a/block/qcow2.h
+++ b/block/qcow2.h
@@ -150,6 +150,12 @@ static inline int size_to_clusters(BDRVQcowState *s,
int64_t size)
return (size + (s->cluster_size - 1)) >> s->cluster_bits;
}
+static inline int size_to_l1(BDRVQcowState *s, int64_t size)
+{
+ int shift = s->cluster_bits + s->l2_bits;
+ return (size + (1ULL << shift) - 1) >> shift;
+}
+
static inline int64_t align_offset(int64_t offset, int n)
{
offset = (offset + n - 1) & ~(n - 1);
--
1.7.0
- [Qemu-devel] [PATCH v2] qcow2: Implement bdrv_truncate() for growing images,
Stefan Hajnoczi <=