linux-kernel - Re: [PATCH v3] module: create weak dependecies

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Message-ID: <ZnHlrLI-XLkfhQBX@bombadil.infradead.org>
Date: Tue, 18 Jun 2024 12:53:16 -0700
From: Luis Chamberlain <mcgrof@...nel.org>
To: Lucas De Marchi <lucas.demarchi@...el.com>
Cc: Jose Ignacio Tornos Martinez <jtornosm@...hat.com>,
	linux-modules@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] module: create weak dependecies

On Tue, May 14, 2024 at 09:25:55AM -0500, Lucas De Marchi wrote:
> On Fri, May 10, 2024 at 10:57:22AM GMT, Jose Ignacio Tornos Martinez wrote:
> > It has been seen that for some network mac drivers (i.e. lan78xx) the
> > related module for the phy is loaded dynamically depending on the current
> > hardware. In this case, the associated phy is read using mdio bus and then
> > the associated phy module is loaded during runtime (kernel function
> > phy_request_driver_module). However, no software dependency is defined, so
> > the user tools will no be able to get this dependency. For example, if
> > dracut is used and the hardware is present, lan78xx will be included but no
> > phy module will be added, and in the next restart the device will not work
> > from boot because no related phy will be found during initramfs stage.
> > 
> > In order to solve this, we could define a normal 'pre' software dependency
> > in lan78xx module with all the possible phy modules (there may be some),
> > but proceeding in that way, all the possible phy modules would be loaded
> > while only one is necessary.
> > 
> > The idea is to create a new type of dependency, that we are going to call
> > 'weak' to be used only by the user tools that need to detect this situation.
> > In that way, for example, dracut could check the 'weak' dependency of the
> > modules involved in order to install these dependencies in initramfs too.
> > That is, for the commented lan78xx module, defining the 'weak' dependency
> > with the possible phy modules list, only the necessary phy would be loaded
> > on demand keeping the same behavior, but all the possible phy modules would
> > be available from initramfs.
> > 
> > The 'weak' dependency support has been included in kmod:
> > https://github.com/kmod-project/kmod/commit/05828b4a6e9327a63ef94df544a042b5e9ce4fe7
> > But, take into account that this can only be used if depmod is new enough.
> > If it isn't, depmod will have the same behavior as always (keeping backward
> > compatibility) and the information for the 'weak' dependency will not be
> > provided.
> > 
> > Signed-off-by: Jose Ignacio Tornos Martinez <jtornosm@...hat.com>
> 
> 
> Reviewed-by: Lucas De Marchi <lucas.demarchi@...el.com>

Thanks! Applied and pushed to modules-next.

  Luis