Re: [Qemu-devel] [PATCH V5 1/5] snapshot: distinguish id and name in load_tmp

[Kevin Wolf]

Am 10.11.2013 um 23:03 hat Wenchao Xia geschrieben:
> Since later this function will be used so improve it. The only caller of it
> now is qemu-img, and it is not impacted by introduce function
> bdrv_snapshot_load_tmp_by_id_or_name() that call bdrv_snapshot_load_tmp()
> twice to keep old search logic. bdrv_snapshot_load_tmp_by_id_or_name() return
> int to let caller know the errno, and errno will be used later.
> Also fix a typo in comments of bdrv_snapshot_delete().
> 
> Signed-off-by: Wenchao Xia <address@hidden>
> ---
>  block/qcow2-snapshot.c    |   16 ++++++++++-
>  block/qcow2.h             |    5 +++-
>  block/snapshot.c          |   60 ++++++++++++++++++++++++++++++++++++++++++--
>  include/block/block_int.h |    4 ++-
>  include/block/snapshot.h  |    7 ++++-
>  qemu-img.c                |    8 ++++-
>  6 files changed, 90 insertions(+), 10 deletions(-)
> 
> diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
> index 3529c68..aeb5efd 100644
> --- a/block/qcow2-snapshot.c
> +++ b/block/qcow2-snapshot.c
> @@ -675,7 +675,10 @@ int qcow2_snapshot_list(BlockDriverState *bs, 
> QEMUSnapshotInfo **psn_tab)
>      return s->nb_snapshots;
>  }
>  
> -int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name)
> +int qcow2_snapshot_load_tmp(BlockDriverState *bs,
> +                            const char *snapshot_id,
> +                            const char *name,
> +                            Error **errp)
>  {
>      int i, snapshot_index;
>      BDRVQcowState *s = bs->opaque;
> @@ -683,12 +686,17 @@ int qcow2_snapshot_load_tmp(BlockDriverState *bs, const 
> char *snapshot_name)
>      uint64_t *new_l1_table;
>      int new_l1_bytes;
>      int ret;
> +    const char *device = bdrv_get_device_name(bs);

This is wrong, low-level functions shouldn't need the device name for
anything.

>      assert(bs->read_only);
>  
>      /* Search the snapshot */
> -    snapshot_index = find_snapshot_by_id_or_name(bs, snapshot_name);
> +    snapshot_index = find_snapshot_by_id_and_name(bs, snapshot_id, name);
>      if (snapshot_index < 0) {
> +        error_setg(errp,
> +                   "Can't find a snapshot with ID '%s' and name '%s' "
> +                   "on device '%s'",
> +                   STR_OR_NULL(snapshot_id), STR_OR_NULL(name), device);
>          return -ENOENT;
>      }
>      sn = &s->snapshots[snapshot_index];

I think we already discussed the same thing in the context of a
different series: The caller knows which device and which snapshot name
or ID he used. The only information he really needs is:

    error_setg(errp, "Can't find snapshot");

If in the context of the caller's caller this isn't enough, the caller
can add this information. I doubt that it's even necessary in this case.

> @@ -699,6 +707,10 @@ int qcow2_snapshot_load_tmp(BlockDriverState *bs, const 
> char *snapshot_name)
>  
>      ret = bdrv_pread(bs->file, sn->l1_table_offset, new_l1_table, 
> new_l1_bytes);
>      if (ret < 0) {
> +        error_setg(errp,
> +                   "Failed to read l1 table for snapshot with ID '%s' and 
> name "
> +                   "'%s' on device '%s'",
> +                   sn->id_str, sn->name, device);
>          g_free(new_l1_table);
>          return ret;
>      }
> diff --git a/block/qcow2.h b/block/qcow2.h
> index 922e190..303eb26 100644
> --- a/block/qcow2.h
> +++ b/block/qcow2.h
> @@ -488,7 +488,10 @@ int qcow2_snapshot_delete(BlockDriverState *bs,
>                            const char *name,
>                            Error **errp);
>  int qcow2_snapshot_list(BlockDriverState *bs, QEMUSnapshotInfo **psn_tab);
> -int qcow2_snapshot_load_tmp(BlockDriverState *bs, const char *snapshot_name);
> +int qcow2_snapshot_load_tmp(BlockDriverState *bs,
> +                            const char *snapshot_id,
> +                            const char *name,
> +                            Error **errp);
>  
>  void qcow2_free_snapshots(BlockDriverState *bs);
>  int qcow2_read_snapshots(BlockDriverState *bs);
> diff --git a/block/snapshot.c b/block/snapshot.c
> index a05c0c0..e51a7db 100644
> --- a/block/snapshot.c
> +++ b/block/snapshot.c
> @@ -194,7 +194,7 @@ int bdrv_snapshot_goto(BlockDriverState *bs,
>   * If only @snapshot_id is specified, delete the first one with id
>   * @snapshot_id.
>   * If only @name is specified, delete the first one with name @name.
> - * if none is specified, return -ENINVAL.
> + * if none is specified, return -EINVAL.
>   *
>   * Returns: 0 on success, -errno on failure. If @bs is not inserted, return
>   * -ENOMEDIUM. If @snapshot_id and @name are both NULL, return -EINVAL. If 
> @bs
> @@ -265,18 +265,72 @@ int bdrv_snapshot_list(BlockDriverState *bs,
>      return -ENOTSUP;
>  }
>  
> +/**
> + * Temporarily load an internal snapshot by @snapshot_id and @name.
> + * @bs: block device used in the operation
> + * @snapshot_id: unique snapshot ID, or NULL
> + * @name: snapshot name, or NULL
> + * @errp: location to store error
> + *
> + * If both @snapshot_id and @name are specified, load the first one with
> + * id @snapshot_id and name @name.
> + * If only @snapshot_id is specified, load the first one with id
> + * @snapshot_id.
> + * If only @name is specified, load the first one with name @name.
> + * if none is specified, return -EINVAL.
> + *
> + * Returns: 0 on success, -errno on fail. If @bs is not inserted, return
> + * -ENOMEDIUM. If @bs is not readonly, return -EINVAL. If @bs did not support
> + * internal snapshot, return -ENOTSUP. If qemu can't find one matching @id 
> and

s/one/a/

> + * @name, return -ENOENT. If @bs does not support parameter @snapshot_id or
> + * @name, return -EINVAL.

What do you mean by "bs does not support parameter"? Is this when you
specify a name, but the block driver doesn't use names, but only IDs?

> If @errp != NULL, it will always be filled on
> + * failure.
> + */

The rest looks good.

Kevin