linux-kernel - Re: [Regression] Missing device nodes for ETR, ETF and STM after CONFIG_UEVENT

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Message-ID: <20190726114325.GA18727@kroah.com>
Date:   Fri, 26 Jul 2019 13:43:25 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>
Cc:     Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Mathieu Poirier <mathieu.poirier@...aro.org>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Leo Yan <leo.yan@...aro.org>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [Regression] Missing device nodes for ETR, ETF and STM after
 CONFIG_UEVENT_HELPER=n

On Fri, Jul 26, 2019 at 01:33:16PM +0200, Thomas Petazzoni wrote:
> Hello,
> 
> On Fri, 26 Jul 2019 12:19:25 +0200
> Greg Kroah-Hartman <gregkh@...uxfoundation.org> wrote:
> 
> > > This somehow is not mounting etr, etf, stm devices when uevent-helper is
> > > disabled. Anyways as Suzuki mentioned, using devtmpfs does fix the issue.  
> > 
> > Last I looked (many years ago) mdev requires uevent-helper in order for
> > it to work.  I recommend that if you rely on mdev to keep that option
> > enabled, or to just use devtmpfs and udev :)
> 
> Since Busybox 1.31.0, mdev has gained a daemon mode. In this mode, mdev
> runs in the background, and receives uevent through a netlink socket.
> So there's been some changes in how Busybox mdev works in recent times.

Ideally mdev should switch to what udev did many many years ago and not
do any device node creations and just leave all of that up to devtmpfs.
Then it can just stick to any symlinks and any specific owner:group
permissions that might be wanted separate from the default ones the
kernel provides.

Makes things much simpler and should save a lot of userspace code,
making mdev even smaller.

thanks,

greg k-h