netdev - Re: [PATCH v2] rds: Expose feature parameters via sysfs

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Message-ID: <05ac7bdf-999c-487c-beb2-74153d03f6b1@lunn.ch>
Date: Fri, 13 Jun 2025 17:21:15 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Cc: allison.henderson@...cle.com, netdev@...r.kernel.org,
	linux-rdma@...r.kernel.org, rds-devel@....oracle.com, tj@...nel.org,
	hannes@...xchg.org, mkoutny@...e.com, cgroups@...r.kernel.org
Subject: Re: [PATCH v2] rds: Expose feature parameters via sysfs

On Wed, Jun 11, 2025 at 06:39:19PM -0400, Konrad Rzeszutek Wilk wrote:
> We would like to have a programatic way for applications
> to query which of the features defined in include/uapi/linux/rds.h
> are actually implemented by the kernel.
> 
> The problem is that applications can be built against newer
> kernel (or older) and they may have the feature implemented or not.
> 
> The lack of a certain feature would signify that the kernel
> does not support it. The presence of it signifies the existence
> of it.
> 
> This would provide the application to query the sysfs and figure
> out what is supported.
> 
> This patch would expose this extra sysfs file:
> 
> /sys/kernel/rds/features

This should probably be documented somewhere under
Documentation/ABI/stable.

> which would contain string values of what the RDS driver supports.
> 
> Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> ---
>  net/rds/af_rds.c | 37 +++++++++++++++++++++++++++++++++++++
>  1 file changed, 37 insertions(+)
> 
> diff --git a/net/rds/af_rds.c b/net/rds/af_rds.c
> index 8435a20968ef..46cb8655df20 100644
> --- a/net/rds/af_rds.c
> +++ b/net/rds/af_rds.c
> @@ -33,6 +33,7 @@
>  #include <linux/module.h>
>  #include <linux/errno.h>
>  #include <linux/kernel.h>
> +#include <linux/kobject.h>
>  #include <linux/gfp.h>
>  #include <linux/in.h>
>  #include <linux/ipv6.h>
> @@ -871,6 +872,33 @@ static void rds6_sock_info(struct socket *sock, unsigned int len,
>  }
>  #endif
>  
> +#ifdef CONFIG_SYSFS

include/linux/sysfs.h has a stub for when SYSFS is not enabled. So you
should not need any #ifdefs

    Andrew

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