Re: [PATCH v2 11/36] block: bdrv_refresh_perms: check parents compliance

[Kevin Wolf <kwolf@redhat.com>]

Am 27.11.2020 um 15:44 hat Vladimir Sementsov-Ogievskiy geschrieben:
> Add additional check that node parents do not interfere with each
> other. This should not hurt existing callers and allows in further
> patch use bdrv_refresh_perms() to update a subtree of changed
> BdrvChild (check that change is correct).
> 
> New check will substitute bdrv_check_update_perm() in following
> permissions refactoring, so keep error messages the same to avoid
> unit test result changes.
> 
> Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

The change itself looks ok, but I'm not happy with the naming. It feels
a bit unspecific. How about inverting the result and calling it
bdrv_parent_perms_conflict() and bdrv_child_perms_conflict()?

At least, I'd call it "permission consistency" rather then "compliance".

> diff --git a/block.c b/block.c
> index 29082c6d47..a756f3e8ad 100644
> --- a/block.c
> +++ b/block.c
> @@ -1966,6 +1966,57 @@ bool bdrv_is_writable(BlockDriverState *bs)
>      return bdrv_is_writable_after_reopen(bs, NULL);
>  }
>  
> +static char *bdrv_child_user_desc(BdrvChild *c)
> +{
> +    if (c->klass->get_parent_desc) {
> +        return c->klass->get_parent_desc(c);
> +    }
> +
> +    return g_strdup("another user");
> +}
> +
> +static bool bdrv_a_allow_b(BdrvChild *a, BdrvChild *b, Error **errp)
> +{
> +    g_autofree char *user = NULL;
> +    g_autofree char *perm_names = NULL;
> +
> +    if ((b->perm & a->shared_perm) == b->perm) {
> +        return true;
> +    }
> +
> +    perm_names = bdrv_perm_names(b->perm & ~a->shared_perm);
> +    user = bdrv_child_user_desc(a);
> +    error_setg(errp, "Conflicts with use by %s as '%s', which does not "
> +               "allow '%s' on %s",
> +               user, a->name, perm_names, bdrv_get_node_name(b->bs));
> +
> +    return false;
> +}
> +
> +static bool bdrv_check_parents_compliance(BlockDriverState *bs, Error **errp)
> +{
> +    BdrvChild *a, *b;
> +
> +    /*
> +     * During the loop we'll look at each pair twice. That's correct is

s/is/because/ or what did you mean here?

> +     * bdrv_a_allow_b() is asymmetric and we should check each pair in both
> +     * directions.
> +     */
> +    QLIST_FOREACH(a, &bs->parents, next_parent) {
> +        QLIST_FOREACH(b, &bs->parents, next_parent) {
> +            if (a == b) {
> +                continue;
> +            }
> +
> +            if (!bdrv_a_allow_b(a, b, errp)) {
> +                return false;
> +            }
> +        }
> +    }
> +
> +    return true;
> +}

Kevin