Re: [PATCH 01/14] block: return status from bdrv_append and friends

[Greg Kurz <groug@kaod.org>]

On Wed,  9 Sep 2020 21:59:17 +0300
Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> wrote:

> The recommended use of qemu error api assumes returning status together
> with setting errp and avoid void functions with errp parameter. Let's
> improve bdrv_append and some friends to reduce error-propagation
> overhead in further patches.
> 
> Choose int return status, because bdrv_replace_node() has call to
> bdrv_check_update_perm(), which reports int status, which seems correct
> to propagate.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
> ---

Reviewed-by: Greg Kurz <groug@kaod.org>

>  include/block/block.h | 12 ++++++------
>  block.c               | 39 ++++++++++++++++++++++++---------------
>  2 files changed, 30 insertions(+), 21 deletions(-)
> 
> diff --git a/include/block/block.h b/include/block/block.h
> index 6e36154061..03b3cee8f8 100644
> --- a/include/block/block.h
> +++ b/include/block/block.h
> @@ -336,10 +336,10 @@ int bdrv_create(BlockDriver *drv, const char* filename,
>  int bdrv_create_file(const char *filename, QemuOpts *opts, Error **errp);
>  
>  BlockDriverState *bdrv_new(void);
> -void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
> -                 Error **errp);
> -void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
> -                       Error **errp);
> +int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
> +                Error **errp);
> +int bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
> +                      Error **errp);
>  
>  int bdrv_parse_aio(const char *mode, int *flags);
>  int bdrv_parse_cache_mode(const char *mode, int *flags, bool *writethrough);
> @@ -351,8 +351,8 @@ BdrvChild *bdrv_open_child(const char *filename,
>                             BdrvChildRole child_role,
>                             bool allow_none, Error **errp);
>  BlockDriverState *bdrv_open_blockdev_ref(BlockdevRef *ref, Error **errp);
> -void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
> -                         Error **errp);
> +int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
> +                        Error **errp);
>  int bdrv_open_backing_file(BlockDriverState *bs, QDict *parent_options,
>                             const char *bdref_key, Error **errp);
>  BlockDriverState *bdrv_open(const char *filename, const char *reference,
> diff --git a/block.c b/block.c
> index 2ba76b2c36..6d35449027 100644
> --- a/block.c
> +++ b/block.c
> @@ -2866,14 +2866,15 @@ static BdrvChildRole bdrv_backing_role(BlockDriverState *bs)
>   * Sets the backing file link of a BDS. A new reference is created; callers
>   * which don't need their own reference any more must call bdrv_unref().
>   */
> -void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
> +int bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
>                           Error **errp)
>  {
> +    int ret = 0;
>      bool update_inherits_from = bdrv_chain_contains(bs, backing_hd) &&
>          bdrv_inherits_from_recursive(backing_hd, bs);
>  
>      if (bdrv_is_backing_chain_frozen(bs, backing_bs(bs), errp)) {
> -        return;
> +        return -EPERM;
>      }
>  
>      if (backing_hd) {
> @@ -2891,15 +2892,22 @@ void bdrv_set_backing_hd(BlockDriverState *bs, BlockDriverState *backing_hd,
>  
>      bs->backing = bdrv_attach_child(bs, backing_hd, "backing", &child_of_bds,
>                                      bdrv_backing_role(bs), errp);
> +    if (!bs->backing) {
> +        ret = -EINVAL;
> +        goto out;
> +    }
> +
>      /* If backing_hd was already part of bs's backing chain, and
>       * inherits_from pointed recursively to bs then let's update it to
>       * point directly to bs (else it will become NULL). */
> -    if (bs->backing && update_inherits_from) {
> +    if (update_inherits_from) {
>          backing_hd->inherits_from = bs;
>      }
>  
>  out:
>      bdrv_refresh_limits(bs, NULL);
> +
> +    return ret;
>  }
>  
>  /*
> @@ -4517,8 +4525,8 @@ static bool should_update_child(BdrvChild *c, BlockDriverState *to)
>      return ret;
>  }
>  
> -void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
> -                       Error **errp)
> +int bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
> +                      Error **errp)
>  {
>      BdrvChild *c, *next;
>      GSList *list = NULL, *p;
> @@ -4540,6 +4548,7 @@ void bdrv_replace_node(BlockDriverState *from, BlockDriverState *to,
>              continue;
>          }
>          if (c->frozen) {
> +            ret = -EPERM;
>              error_setg(errp, "Cannot change '%s' link to '%s'",
>                         c->name, from->node_name);
>              goto out;
> @@ -4575,6 +4584,8 @@ out:
>      g_slist_free(list);
>      bdrv_drained_end(from);
>      bdrv_unref(from);
> +
> +    return ret;
>  }
>  
>  /*
> @@ -4593,20 +4604,16 @@ out:
>   * parents of bs_top after bdrv_append() returns. If the caller needs to keep a
>   * reference of its own, it must call bdrv_ref().
>   */
> -void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
> -                 Error **errp)
> +int bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
> +                Error **errp)
>  {
> -    Error *local_err = NULL;
> -
> -    bdrv_set_backing_hd(bs_new, bs_top, &local_err);
> -    if (local_err) {
> -        error_propagate(errp, local_err);
> +    int ret = bdrv_set_backing_hd(bs_new, bs_top, errp);
> +    if (ret < 0) {
>          goto out;
>      }
>  
> -    bdrv_replace_node(bs_top, bs_new, &local_err);
> -    if (local_err) {
> -        error_propagate(errp, local_err);
> +    ret = bdrv_replace_node(bs_top, bs_new, errp);
> +    if (ret < 0) {
>          bdrv_set_backing_hd(bs_new, NULL, &error_abort);
>          goto out;
>      }
> @@ -4615,6 +4622,8 @@ void bdrv_append(BlockDriverState *bs_new, BlockDriverState *bs_top,
>       * additional reference any more. */
>  out:
>      bdrv_unref(bs_new);
> +
> +    return ret;
>  }
>  
>  static void bdrv_delete(BlockDriverState *bs)