Re: [Qemu-devel] [PATCH V4 2/6] qcow2: add error message in qcow2_write_snapshots()

[Max Reitz <mreitz@redhat.com>]

On 14.10.2013 23:52, Wenchao Xia wrote:
> The function still returns int since qcow2_snapshot_delete() will
> return the number.
>
> Signed-off-by: Wenchao Xia <xiawenc@linux.vnet.ibm.com>
> ---
>  block/qcow2-snapshot.c |   48 ++++++++++++++++++++++++++++++++++++++++++------
>  1 files changed, 42 insertions(+), 6 deletions(-)
>
> diff --git a/block/qcow2-snapshot.c b/block/qcow2-snapshot.c
> index b373f9a..4bd494b 100644
> --- a/block/qcow2-snapshot.c
> +++ b/block/qcow2-snapshot.c
> @@ -152,7 +152,7 @@ fail:
>  }
>  
>  /* add at the end of the file a new list of snapshots */
> -static int qcow2_write_snapshots(BlockDriverState *bs)
> +static int qcow2_write_snapshots(BlockDriverState *bs, Error **errp)
>  {
>      BDRVQcowState *s = bs->opaque;
>      QCowSnapshot *sn;
> @@ -183,10 +183,18 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
>      offset = snapshots_offset;
>      if (offset < 0) {
>          ret = offset;
> +        error_setg(errp,
> +                   "Failed in allocation of cluster for snapshot list: "
> +                   "%d (%s)",
> +                   ret, strerror(-ret));

Again, error_setg_errno() is your friend.

>          goto fail;
>      }
>      ret = bdrv_flush(bs);
>      if (ret < 0) {
> +        error_setg(errp,
> +                   "Failed in flush after snapshot list cluster allocation: "
> +                   "%d (%s)",
> +                   ret, strerror(-ret));
>          goto fail;
>      }
>  
> @@ -194,6 +202,10 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
>       * must indeed be completely free */
>      ret = qcow2_pre_write_overlap_check(bs, 0, offset, snapshots_size);
>      if (ret < 0) {
> +        error_setg(errp,
> +                   "Failed in overlap check for snapshot list cluster at %"
> +                   PRIi64 " with size %d: %d (%s)",
> +                   offset, snapshots_size, ret, strerror(-ret));
>          goto fail;
>      }
>  
> @@ -227,24 +239,40 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
>  
>          ret = bdrv_pwrite(bs->file, offset, &h, sizeof(h));
>          if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed in write of snapshot header at %"
> +                       PRIi64 " with size %" PRIu64 ": %d (%s)",
> +                       offset, sizeof(h), ret, strerror(-ret));

Again, on 32 bit systems, sizeof(size_t) is generally 4 and not 8 (you
may want to cast sizeof(h) to int and just use %d).

>              goto fail;
>          }
>          offset += sizeof(h);
>  
>          ret = bdrv_pwrite(bs->file, offset, &extra, sizeof(extra));
>          if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed in write of extra snapshot data at %"
> +                       PRIi64 " with size %" PRIu64 ": %d (%s)",
> +                       offset, sizeof(extra), ret, strerror(-ret));

Same here.

>              goto fail;
>          }
>          offset += sizeof(extra);
>  
>          ret = bdrv_pwrite(bs->file, offset, sn->id_str, id_str_size);
>          if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed in write of snapshot id string at %"
> +                       PRIi64 " with size %d: %d (%s)",
> +                       offset, id_str_size, ret, strerror(-ret));
>              goto fail;
>          }
>          offset += id_str_size;
>  
>          ret = bdrv_pwrite(bs->file, offset, sn->name, name_size);
>          if (ret < 0) {
> +            error_setg(errp,
> +                       "Failed in write of snapshot name string at %"
> +                       PRIi64 " with size %d: %d (%s)",
> +                       offset, name_size, ret, strerror(-ret));
>              goto fail;
>          }
>          offset += name_size;
> @@ -256,6 +284,9 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
>       */
>      ret = bdrv_flush(bs);
>      if (ret < 0) {
> +        error_setg(errp,
> +                   "Failed in flush after snapshot list update: %d (%s)",
> +                   ret, strerror(-ret));
>          goto fail;
>      }
>  
> @@ -268,6 +299,11 @@ static int qcow2_write_snapshots(BlockDriverState *bs)
>      ret = bdrv_pwrite_sync(bs->file, offsetof(QCowHeader, nb_snapshots),
>                             &header_data, sizeof(header_data));
>      if (ret < 0) {
> +        error_setg(errp,
> +                   "Failed in update of image header at %"
> +                   PRIi64 " with size %" PRIu64 ":%d (%s)",
> +                   offsetof(QCowHeader, nb_snapshots), sizeof(header_data),
> +                   ret, strerror(-ret));

And here (also applies to offsetof(), which returns size_t as well).
Also, you forgot a space after the colon (although you should be using
error_setg_errno() anyway).

Max

>          goto fail;
>      }
>  
> @@ -283,6 +319,9 @@ fail:
>          qcow2_free_clusters(bs, snapshots_offset, snapshots_size,
>                              QCOW2_DISCARD_ALWAYS);
>      }
> +    if (errp) {
> +        g_assert(error_is_set(errp));
> +    }
>      return ret;
>  }
>  
> @@ -446,10 +485,8 @@ void qcow2_snapshot_create(BlockDriverState *bs,
>      s->snapshots = new_snapshot_list;
>      s->snapshots[s->nb_snapshots++] = *sn;
>  
> -    ret = qcow2_write_snapshots(bs);
> +    ret = qcow2_write_snapshots(bs, errp);
>      if (ret < 0) {
> -        /* Following line will be replaced with more detailed error later */
> -        error_setg(errp, "Failed in write of snapshot");
>          g_free(s->snapshots);
>          s->snapshots = old_snapshot_list;
>          s->nb_snapshots--;
> @@ -623,9 +660,8 @@ int qcow2_snapshot_delete(BlockDriverState *bs,
>              s->snapshots + snapshot_index + 1,
>              (s->nb_snapshots - snapshot_index - 1) * sizeof(sn));
>      s->nb_snapshots--;
> -    ret = qcow2_write_snapshots(bs);
> +    ret = qcow2_write_snapshots(bs, errp);
>      if (ret < 0) {
> -        error_setg(errp, "Failed to remove snapshot from snapshot list");
>          return ret;
>      }
>