netdev - Re: [PATCH net] net: dsa: fix error code getting shifted with 4 in dsa_slave_get_sset

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Date:   Sun, 9 May 2021 10:35:27 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Vladimir Oltean <olteanv@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, netdev@...r.kernel.org
Cc:     Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Vladimir Oltean <vladimir.oltean@....com>
Subject: Re: [PATCH net] net: dsa: fix error code getting shifted with 4 in
 dsa_slave_get_sset_count



On 5/9/2021 4:55 AM, Vladimir Oltean wrote:
> From: Vladimir Oltean <vladimir.oltean@....com>
> 
> DSA implements a bunch of 'standardized' ethtool statistics counters,
> namely tx_packets, tx_bytes, rx_packets, rx_bytes. So whatever the
> hardware driver returns in .get_sset_count(), we need to add 4 to that.
> 
> That is ok, except that .get_sset_count() can return a negative error
> code, for example:
> 
> b53_get_sset_count
> -> phy_ethtool_get_sset_count
>    -> return -EIO
> 
> -EIO is -5, and with 4 added to it, it becomes -1, aka -EPERM. One can
> imagine that certain error codes may even become positive, although
> based on code inspection I did not see instances of that.
> 
> Check the error code first, if it is negative return it as-is.
> 
> Based on a similar patch for dsa_master_get_strings from Dan Carpenter:
> https://patchwork.kernel.org/project/netdevbpf/patch/YJaSe3RPgn7gKxZv@mwanda/
> 
> Fixes: 91da11f870f0 ("net: Distributed Switch Architecture protocol support")
> Signed-off-by: Vladimir Oltean <vladimir.oltean@....com>

Reviewed-by: Florian Fainelli <f.fainelli@...il.com>

Just one nit below:

> ---
>  net/dsa/slave.c | 12 +++++++-----
>  1 file changed, 7 insertions(+), 5 deletions(-)
> 
> diff --git a/net/dsa/slave.c b/net/dsa/slave.c
> index 3689ffa2dbb8..dda232a8d6f5 100644
> --- a/net/dsa/slave.c
> +++ b/net/dsa/slave.c
> @@ -798,13 +798,15 @@ static int dsa_slave_get_sset_count(struct net_device *dev, int sset)
>  	struct dsa_switch *ds = dp->ds;
>  
>  	if (sset == ETH_SS_STATS) {
> -		int count;
> +		int err = 0;
>  
> -		count = 4;
> -		if (ds->ops->get_sset_count)
> -			count += ds->ops->get_sset_count(ds, dp->index, sset);
> +		if (ds->ops->get_sset_count) {
> +			err = ds->ops->get_sset_count(ds, dp->index, sset);
> +			if (err < 0)
> +				return err;
> +		}
>  
> -		return count;

I would have a preference for keeping the count variable and treating it
specifically in case it is negative.
-- 
Florian