linux-kernel - Re: [PATCH] net: drop_monitor: use IS_REACHABLE() to guard net_dm_hw

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Date:   Wed, 11 Mar 2020 11:31:43 +0200
From:   Ido Schimmel <idosch@...lanox.com>
To:     Masahiro Yamada <masahiroy@...nel.org>, nhorman@...driver.com,
        jiri@...lanox.com
Cc:     netdev@...r.kernel.org, "David S . Miller" <davem@...emloft.net>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        Nicolas Pitre <nico@...xnic.net>, linux-kbuild@...r.kernel.org,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] net: drop_monitor: use IS_REACHABLE() to guard
 net_dm_hw_report()

On Wed, Mar 11, 2020 at 03:29:25PM +0900, Masahiro Yamada wrote:
> In net/Kconfig, NET_DEVLINK implies NET_DROP_MONITOR.
> 
> The original behavior of the 'imply' keyword prevents NET_DROP_MONITOR
> from being 'm' when NET_DEVLINK=y.
> 
> With the planned Kconfig change that relaxes the 'imply', the
> combination of NET_DEVLINK=y and NET_DROP_MONITOR=m would be allowed.
> 
> Use IS_REACHABLE() to avoid the vmlinux link error for this case.
> 
> Reported-by: Stephen Rothwell <sfr@...b.auug.org.au>
> Signed-off-by: Masahiro Yamada <masahiroy@...nel.org>

Thanks, Masahiro.

Neil, Jiri, another option (long term) is to add a raw tracepoint (not
part of ABI) in devlink and have drop monitor register its probe on it
when monitoring.

Two advantages:
1. Consistent with what drop monitor is already doing with kfree_skb()
tracepoint
2. We can remove 'imply NET_DROP_MONITOR' altogether

What do you think?