linux-kernel - Re: [PATCH] firmware_loader: re-export fw_fallback_config into firmware

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Message-ID: <20200423192716.2c32f5dd@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Thu, 23 Apr 2020 19:27:16 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Luis Chamberlain <mcgrof@...nel.org>
Cc:     gregkh@...uxfoundation.org, akpm@...ux-foundation.org,
        josh@...htriplett.org, rishabhb@...eaurora.org, maco@...roid.com,
        andy.gross@...aro.org, david.brown@...aro.org,
        bjorn.andersson@...aro.org, linux-wireless@...r.kernel.org,
        keescook@...omium.org, shuah@...nel.org, mfuzzey@...keon.com,
        zohar@...ux.vnet.ibm.com, dhowells@...hat.com,
        pali.rohar@...il.com, tiwai@...e.de, arend.vanspriel@...adcom.com,
        zajec5@...il.com, nbroeking@...com, markivx@...eaurora.org,
        broonie@...nel.org, dmitry.torokhov@...il.com, dwmw2@...radead.org,
        torvalds@...ux-foundation.org, Abhay_Salunke@...l.com,
        jewalt@...innovations.com, cantabile.desu@...il.com, ast@...com,
        andresx7@...il.com, dan.rue@...aro.org, brendanhiggins@...gle.com,
        yzaikin@...gle.com, linux-kernel@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, Christoph Hellwig <hch@....de>,
        Randy Dunlap <rdunlap@...radead.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH] firmware_loader: re-export fw_fallback_config into
 firmware_loader's own namespace

On Fri, 24 Apr 2020 02:14:20 +0000 Luis Chamberlain wrote:
> On Thu, Apr 23, 2020 at 06:05:44PM -0700, Jakub Kicinski wrote:
> > On Thu, 23 Apr 2020 20:31:40 +0000 Luis R. Rodriguez wrote:  
> > > From: Luis Chamberlain <mcgrof@...nel.org>
> > > 
> > > Christoph's recent patch "firmware_loader: remove unused exports", which
> > > is not merged upstream yet, removed two exported symbols. One is fine to
> > > remove since only built-in code uses it but the other is incorrect.
> > > 
> > > If CONFIG_FW_LOADER=m so the firmware_loader is modular but
> > > CONFIG_FW_LOADER_USER_HELPER=y we fail at mostpost with:
> > > 
> > > ERROR: modpost: "fw_fallback_config" [drivers/base/firmware_loader/firmware_class.ko] undefined!
> > > 
> > > This happens because the variable fw_fallback_config is built into the
> > > kernel if CONFIG_FW_LOADER_USER_HELPER=y always, so we need to grant
> > > access to the firmware loader module by exporting it.
> > > 
> > > Instead of just exporting it as we used to, take advantage of the new
> > > kernel symbol namespacing functionality, and export the symbol only to
> > > the firmware loader private namespace. This would prevent misuses from
> > > other drivers and makes it clear the goal is to keep this private to
> > > the firmware loader alone.
> > > 
> > > Cc: Christoph Hellwig <hch@....de>
> > > Cc: Randy Dunlap <rdunlap@...radead.org>
> > > Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> > > Fixes: "firmware_loader: remove unused exports"  
> > 
> > Can't help but notice this strange form of the Fixes tag, is it
> > intentional?  
> 
> Yeah, no there is no commit for the patch as the commit is ephemeral in
> a development tree not yet upstream, ie, not on Linus' tree yet. Using a
> commit here then makes no sense unless one wants to use a reference
> development tree in this case, as development trees are expected to
> rebase to move closer towards Linus' tree. When a tree rebases, the
> commit IDs change, and this is why the commit is ephemeral unless
> one uses a base tree / branch / tag.

I'd think that either the commit is rebase-able and the fix can be
squashed into it, or it's not and it has a stable commit id. 
But I guess it may get tricky around the edges..