On 21.02.2017 15:58, Kevin Wolf wrote:
> In many cases, the required permissions of one node on its children
> depends on what its parents require from it. For example, the raw format

*depend

> or most filter drivers only need to request consistent reads if that's
> something that one of their parents wants.
> 
> In order to achieve this, this patch introduces two new BlockDriver
> callbacks. The first one lets drivers first check (recursively) whether
> the requested permissions can be set; the second one actually sets the
> new permission bitmask.
> 
> Also add helper functions that drivers can use in their implementation
> of the callbacks to update their permissions on a specific child.
> 
> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
> ---
>  block.c                   | 176 ++++++++++++++++++++++++++++++++++++++++++++++
>  include/block/block_int.h |  61 ++++++++++++++++
>  2 files changed, 237 insertions(+)
> 
> diff --git a/block.c b/block.c
> index d9f2267..2a86781 100644
> --- a/block.c
> +++ b/block.c
> @@ -1326,11 +1326,145 @@ static int bdrv_fill_options(QDict **options, const char *filename,

[...]

> +/*
> + * Notifies drivers that after a previous bdrv_check_perm() call, the
> + * permission update is not performed and any preparations made for it (e.g.
> + * taken file locks) need to be undone.
> + *
> + * This function recursively notifies all child nodes.
> + */
> +static void bdrv_abort_perm_update(BlockDriverState *bs)
> +{
> +    BlockDriver *drv = bs->drv;
> +    BdrvChild *c;
> +
> +    if (!drv) {
> +        return;
> +    }
> +
> +    if (drv->bdrv_abort_perm_update) {
> +        drv->bdrv_abort_perm_update(bs);
> +    }
> +
> +    QLIST_FOREACH(c, &bs->children, next) {
> +        bdrv_abort_perm_update(c->bs);

Could use bdrv_child_abort_perm_update(c) just for symmetry with
bdrv_check_perm() (which uses bdrv_child_check_perm() to recurse).

> +    }
> +}
> +

[...]

> @@ -1353,8 +1487,47 @@ static int bdrv_check_update_perm(BlockDriverState *bs, uint64_t new_used_perm,
>              error_setg(errp, "Conflicts with %s", user ?: "another operation");
>              return -EPERM;
>          }
> +
> +        cumulative_perms |= c->perm;
> +        cumulative_shared_perms &= c->shared_perm;
> +    }
> +
> +    return bdrv_check_perm(bs, cumulative_perms, cumulative_shared_perms, errp);
> +}
> +
> +/* Needs to be followed by a call to either bdrv_set_perm() or
> + * bdrv_abort_perm_update(). */

*"bdrv_child_set_perm() or bdrv_child_abort_perm_update()"?

(Doesn't really matter, but it makes for nicer symmetry.)

> +int bdrv_child_check_perm(BdrvChild *c, uint64_t perm, uint64_t shared,
> +                          Error **errp)
> +{
> +    return bdrv_check_update_perm(c->bs, perm, shared, c, errp);
> +}

[...]

> @@ -1390,6 +1565,7 @@ BdrvChild *bdrv_root_attach_child(BlockDriverState *child_bs,
>  
>      ret = bdrv_check_update_perm(child_bs, perm, shared_perm, NULL, errp);
>      if (ret < 0) {
> +        bdrv_abort_perm_update(child_bs);
>          return NULL;
>      }
>  

This function doesn't call bdrv_set_perm(). Intentional?

Max

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