netdev - Re: [RFC PATCH net-next 1/6] net: ethtool: attach an IDR of custom RSS contexts to a netdevice

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Date:   Tue, 4 Apr 2023 12:30:42 +0100
From:   Edward Cree <ecree.xilinx@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>, edward.cree@....com
Cc:     linux-net-drivers@....com, davem@...emloft.net, pabeni@...hat.com,
        edumazet@...gle.com, netdev@...r.kernel.org,
        habetsm.xilinx@...il.com, sudheer.mogilappagari@...el.com
Subject: Re: [RFC PATCH net-next 1/6] net: ethtool: attach an IDR of custom
 RSS contexts to a netdevice

On 03/04/2023 22:43, Jakub Kicinski wrote:
> On Mon, 3 Apr 2023 17:32:58 +0100 edward.cree@....com wrote:
>> +	/* private: indirection table, hash key, and driver private data are
>> +	 * stored sequentially in @data area.  Use below helpers to access
>> +	 */
>> +	u8 data[];
> 
> I think that something needs to get aligned here...
> Driver priv needs to guarantee ulong alignment in case someone puts 
> a pointer in it.
> 
>> +static inline void *ethtool_rxfh_context_priv(struct ethtool_rxfh_context *ctx)
>> +{
>> +	return ethtool_rxfh_context_key(ctx) + ctx->key_size;
> 
> ALIGN_PTR() ... ?
> Or align data[] and reorder..

Very good points.  Indir also needs 4-byte alignment.
Will fix in next version.

>> +	u32			rss_ctx_max_id;
>> +	struct idr		rss_ctx;
> 
> noob question, why not xarray?

Because I know how to use the IDR API, but have never used
 xarray directly, so would need to learn it.

> Isn't IDR just a legacy wrapper around xarray anyway?

I see it as a *convenience* wrapper.  Is it deprecated?