linux-kernel - Re: RFC: Handle hard module dependencies that are not symbol-based (r8169 + realtek)

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Date:   Wed, 8 Apr 2020 23:37:23 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Lucas De Marchi <lucas.demarchi@...el.com>,
        Jessica Yu <jeyu@...nel.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-modules@...r.kernel.org,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: RFC: Handle hard module dependencies that are not symbol-based
 (r8169 + realtek)

On 01.04.2020 23:20, Heiner Kallweit wrote:
> Currently we have no way to express a hard dependency that is not
> a symbol-based dependency (symbol defined in module A is used in
> module B). Use case:
> Network driver ND uses callbacks in the dedicated PHY driver DP
> for the integrated PHY (namely read_page() and write_page() in
> struct phy_driver). If DP can't be loaded (e.g. because ND is in
> initramfs but DP is not), then phylib will use the generic
> PHY driver GP. GP doesn't implement certain callbacks that are
> needed by ND, therefore ND's probe has to bail out with an error
> once it detects that DP is not loaded.
> We have this problem with driver r8169 having such a dependency
> on PHY driver realtek. Some distributions have tools for
> configuring initramfs that consider hard dependencies based on
> depmod output. Means so far somebody can add r8169.ko to initramfs,
> and neither human being nor machine will have an idea that
> realtek.ko needs to be added too.
> 
> Attached patch set (two patches for kmod, one for the kernel)
> allows to express this hard dependency of ND from DP. depmod will
> read this dependency information and treat it like a symbol-based
> dependency. As a result tools e.g. populating initramfs can
> consider the dependency and place DP in initramfs if ND is in
> initramfs. On my system the patch set does the trick when
> adding following line to r8169_main.c:
> MODULE_HARDDEP("realtek");
> 
> I'm interested in your opinion on the patches, and whether you
> maybe have a better idea how to solve the problem.
> 
> Heiner
> 
Any feedback?

Thanks, Heiner