netdev - Re: [PATCH net-next v7 4/9] devlink: Allow for devlink-rate nodes parent reassignment

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Message-Id: <20221027223414.11627-1-przemyslaw.kitszel@intel.com>
Date:   Fri, 28 Oct 2022 00:34:14 +0200
From:   Przemek Kitszel <przemyslaw.kitszel@...el.com>
To:     netdev@...r.kernel.org
Cc:     Przemek Kitszel <przemyslaw.kitszel@...el.com>,
        alexandr.lobakin@...el.com, jacob.e.keller@...el.com,
        jesse.brandeburg@...el.com, anthony.l.nguyen@...el.com,
        kuba@...nel.org, ecree.xilinx@...il.com, jiri@...nulli.us,
        Michal Wilczynski <michal.wilczynski@...el.com>
Subject: Re: [PATCH net-next v7 4/9] devlink: Allow for devlink-rate nodes parent reassignment

From:   Michal Wilczynski <michal.wilczynski@...el.com>
Date:   Thu, 27 Oct 2022 15:00:44 +0200

[...]

> diff --git a/net/core/devlink.c b/net/core/devlink.c
> index 864fa0967b7a..1e0c1b0376bf 100644
> --- a/net/core/devlink.c
> +++ b/net/core/devlink.c
> @@ -1875,10 +1875,9 @@ devlink_nl_rate_parent_node_set(struct devlink_rate *devlink_rate,
>  	int err = -EOPNOTSUPP;
>  
>  	parent = devlink_rate->parent;
> -	if (parent && len) {
> -		NL_SET_ERR_MSG_MOD(info->extack, "Rate object already has parent.");
> -		return -EBUSY;
> -	} else if (parent && !len) {
> +
> +	/* if a parent is already set, just reassign the parent */
> +	if (parent && !len) {

Comment that you have added should be placed way below, here it is misleading.

>  		if (devlink_rate_is_leaf(devlink_rate))
>  			err = ops->rate_leaf_parent_set(devlink_rate, NULL,
>  							devlink_rate->priv, NULL,
> @@ -1892,7 +1891,7 @@ devlink_nl_rate_parent_node_set(struct devlink_rate *devlink_rate,
>  
>  		refcount_dec(&parent->refcnt);
>  		devlink_rate->parent = NULL;
> -	} else if (!parent && len) {
> +	} else if (len) {
>  		parent = devlink_rate_node_get_by_name(devlink, parent_name);
>  		if (IS_ERR(parent))
>  			return -ENODEV;
> @@ -1919,6 +1918,10 @@ devlink_nl_rate_parent_node_set(struct devlink_rate *devlink_rate,
>  		if (err)
>  			return err;
>  

Comment above makes more sense here, likely combined with the one just below.

> +		if (devlink_rate->parent)
> +			/* we're reassigning to other parent in this case */
> +			refcount_dec(&devlink_rate->parent->refcnt);
> +
>  		refcount_inc(&parent->refcnt);
>  		devlink_rate->parent = parent;
>  	}
> --

Thanks for splitting this patch out of the other, change itself is easier 
to follow now. Code (modulo comments) is correct, you could add my Reviewed-by
after comment fix.

Side note: ops (rate_{leaf|node}_parent_set) lack documentation. There is also 
not much usage of them as of now, so maybe we could extend them to actually do
refcount_inc + refcount_dec (if applicable) + set pointers.
OTOH: As of now those are more of "on-event" callbacks, not "do-something", 
what is further confirmed in name (word "set" on the end, not begining).

--PK