On Tue, Apr 01, 2014 at 02:06:10PM +0800, Jun Li wrote:
> Signed-off-by: Jun Li <junm...@gmail.com>
>
> This patch can make sure the data still existing after shrinking. And only
> discard the unused (guest) clusters. If shrinking to the size which stored
> data, It will return an error and will not do any change.
> As this patch can support shrinking, so changed the func name of
> qcow2_grow_l1_table to qcow2_truncate_l1_table.
Please follow the patch formatting conventions:
qcow2: add qcow2_truncate() shrinking support
...patch description...
Signed-off-by: ...
> -int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> +int qcow2_truncate_l1_table(BlockDriverState *bs, uint64_t min_size,
> bool exact_size)
> {
> BDRVQcowState *s = bs->opaque;
> @@ -39,9 +39,6 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t
> min_size,
> int64_t new_l1_table_offset, new_l1_size;
> uint8_t data[12];
>
> - if (min_size <= s->l1_size)
> - return 0;
> -
> if (exact_size) {
> new_l1_size = min_size;
> } else {
> @@ -66,7 +63,18 @@ int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t
> min_size,
>
> new_l1_size2 = sizeof(uint64_t) * new_l1_size;
> new_l1_table = g_malloc0(align_offset(new_l1_size2, 512));
> - memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
> +
> + /* shrinking the image */
> + if (min_size <= s->l1_size) {
> + if (s->l1_table[new_l1_size] != 0) {
> + error_report("Could not shrink to this size, "
> + "it will destory image data");
> + return -ENOTSUP;
> + }
> + memcpy(new_l1_table, s->l1_table, new_l1_size2);
> + }
> +
> + memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
In the shrink case the second memcpy() overflows new_l1_table.
But the bigger issue I see with this patch is that bdrv_truncate() is
supposed to shrink the file, whether there is data present or not.
Please drop the if (s->l1_table[new_l1_size] != 0) test.
>
> /* write new table (align to cluster) */
> BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);
> @@ -559,7 +567,7 @@ static int get_cluster_table(BlockDriverState *bs,
> uint64_t offset,
>
> l1_index = offset >> (s->l2_bits + s->cluster_bits);
> if (l1_index >= s->l1_size) {
> - ret = qcow2_grow_l1_table(bs, l1_index + 1, false);
> + ret = qcow2_truncate_l1_table(bs, l1_index + 1, false);
> if (ret < 0) {
> return ret;
> }
> diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
> index 2fc6320..ab16c52 100644
> --- a/block/qcow2-snapshot.c
> +++ b/block/qcow2-snapshot.c
> @@ -491,7 +491,7 @@ int qcow2_snapshot_goto(BlockDriverState *bs, const char
> *snapshot_id)
> * L1 table of the snapshot. If the snapshot L1 table is smaller, the
> * current one must be padded with zeros.
> */
> - ret = qcow2_grow_l1_table(bs, sn->l1_size, true);
> + ret = qcow2_truncate_l1_table(bs, sn->l1_size, true);
> if (ret < 0) {
> goto fail;
> }
> diff --git a/block/qcow2.c b/block/qcow2.c
> index b9dc960..4797879 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1764,14 +1764,8 @@ static int qcow2_truncate(BlockDriverState *bs,
> int64_t offset)
> return -ENOTSUP;
> }
>
> - /* shrinking is currently not supported */
> - if (offset < bs->total_sectors * 512) {
> - error_report("qcow2 doesn't support shrinking images yet");
> - return -ENOTSUP;
> - }
> -
> new_l1_size = size_to_l1(s, offset);
> - ret = qcow2_grow_l1_table(bs, new_l1_size, true);
> + ret = qcow2_truncate_l1_table(bs, new_l1_size, true);
> if (ret < 0) {
> return ret;
> }
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 0b0eac8..298d84e 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -455,7 +455,7 @@ int qcow2_pre_write_overlap_check(BlockDriverState *bs,
> int ign, int64_t offset,
> int64_t size);
>
> /* qcow2-cluster.c functions */
> -int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> +int qcow2_truncate_l1_table(BlockDriverState *bs, uint64_t min_size,
> bool exact_size);
Please indent "bool exact_size" up to the '(':
+int qcow2_truncate_l1_table(BlockDriverState *bs, uint64_t min_size,
+ bool exact_size);
