Re: [PATCH] qcow2: Patch for shrinking qcow2 disk image

As the realization of raw shrinking, so when do qcow2 shrinking, do not
check l1 entries. When resize to size1(size1 < "disk size"), the custemer
knows this will destory the data. So no need to check the l1 entries which
is used or not.
BTW, there will possible be "disk size" > "virtual size". As this, when do
qcow2 shrinking, we should to discard the unused clusters(reduce the refcount
of the unused clusters, release these clusters).
This is the update patch. thx.

Signed-off-by: Jun Li <junmuzi@gmail.com>
---
 block/qcow2-cluster.c  | 16 +++++++++++-----
 block/qcow2-snapshot.c |  2 +-
 block/qcow2.c          | 10 ++--------
 block/qcow2.h          |  4 ++--
 4 files changed, 16 insertions(+), 16 deletions(-)

Hi list,
    Ping. Could someone help to review this patch, thank you very much. 
The following is the patch url:
http://lists.nongnu.org/archive/html/qemu-devel/2014-04/msg00805.html

On 04/05/2014 12:52 AM, Jun Li wrote:
> As the realization of raw shrinking, so when do qcow2 shrinking, do not
> check l1 entries. When resize to size1(size1 < "disk size"), the custemer
> knows this will destory the data. So no need to check the l1 entries which
> is used or not.
> BTW, there will possible be "disk size" > "virtual size". As this, when do
> qcow2 shrinking, we should to discard the unused clusters(reduce the refcount
> of the unused clusters, release these clusters).
> This is the update patch. thx.
>
> Signed-off-by: Jun Li <junmuzi@gmail.com>
> ---
>   block/qcow2-cluster.c  | 16 +++++++++++-----
>   block/qcow2-snapshot.c |  2 +-
>   block/qcow2.c          | 10 ++--------
>   block/qcow2.h          |  4 ++--
>   4 files changed, 16 insertions(+), 16 deletions(-)
>
> diff --git a/block/qcow2-cluster.c b/block/qcow2-cluster.c
> index 60a6910..5ccc2a4 100644
> --- a/block/qcow2-cluster.c
> +++ b/block/qcow2-cluster.c
> @@ -29,8 +29,8 @@
>   #include "block/qcow2.h"
>   #include "trace.h"
>   
> -int qcow2_grow_l1_table(BlockDriverState *bs, uint64_t min_size,
> -                        bool exact_size)
> +int qcow2_truncate_l1_table(BlockDriverState *bs, uint64_t min_size,
> +                            bool exact_size)
>   {
>       BDRVQcowState *s = bs->opaque;
>       int new_l1_size2, ret, i;
> @@ -39,7 +39,7 @@ 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)
> +    if (min_size == s->l1_size)
>           return 0;
>   
>       if (exact_size) {
> @@ -66,7 +66,13 @@ 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 or growing l1 table */
> +    if (min_size < s->l1_size) {
> +        memcpy(new_l1_table, s->l1_table, new_l1_size2);
> +    } else {
> +        memcpy(new_l1_table, s->l1_table, s->l1_size * sizeof(uint64_t));
> +    }
>   
>       /* write new table (align to cluster) */
>       BLKDBG_EVENT(bs->file, BLKDBG_L1_GROW_ALLOC_TABLE);
> @@ -550,7 +556,7 @@ 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 0aa9def..6ba460e 100644
> --- a/block/qcow2-snapshot.c
> +++ b/block/qcow2-snapshot.c
> @@ -483,7 +483,7 @@ 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 333e26d..4fe580e 100644
> --- a/block/qcow2.c
> +++ b/block/qcow2.c
> @@ -1858,7 +1858,7 @@ static int qcow2_truncate(BlockDriverState *bs, int64_t offset)
>       int64_t new_l1_size;
>       int ret;
>   
> -    if (offset & 511) {
> +    if (offset <= 0 || offset & 511) {
>           error_report("The new size must be a multiple of 512");
>           return -EINVAL;
>       }
> @@ -1869,14 +1869,8 @@ 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 b49424b..fa36930 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -499,8 +499,8 @@ 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,
> -                        bool exact_size);
> +int qcow2_truncate_l1_table(BlockDriverState *bs, uint64_t min_size,
> +                            bool exact_size);
>   int qcow2_write_l1_entry(BlockDriverState *bs, int l1_index);
>   void qcow2_l2_cache_reset(BlockDriverState *bs);
>   int qcow2_decompress_cluster(BlockDriverState *bs, uint64_t cluster_offset);