linux-kernel - Re: [PATCH] of: Add printf '%pOFm' for generating modalias

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Message-ID: <20241230205230.GB2488017-robh@kernel.org>
Date: Mon, 30 Dec 2024 14:52:30 -0600
From: Rob Herring <robh@...nel.org>
To: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc: Petr Mladek <pmladek@...e.com>, Steven Rostedt <rostedt@...dmis.org>,
	Rasmus Villemoes <linux@...musvillemoes.dk>,
	Sergey Senozhatsky <senozhatsky@...omium.org>,
	Jonathan Corbet <corbet@....net>,
	Saravana Kannan <saravanak@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Zijun Hu <quic_zijuhu@...cinc.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, devicetree@...r.kernel.org
Subject: Re: [PATCH] of: Add printf '%pOFm' for generating modalias

On Mon, Dec 23, 2024 at 09:58:27PM +0200, Andy Shevchenko wrote:
> On Tue, Dec 17, 2024 at 12:37:09PM -0600, Rob Herring (Arm) wrote:
> > The callers for of_modalias() generally need the module alias as part of
> > some larger string. That results in some error prone manipulation of the
> > buffer prepend/append the module alias string. In fact,
> > of_device_uevent_modalias() has several issues. First, it's off by one
> > too few characters in utilization of the full buffer. Second, the error
> > paths leave OF_MODALIAS with a truncated value when in the end nothing
> > should be added to the buffer. It is also fragile because it needs
> > internal details of struct kobj_uevent_env. add_uevent_var() really
> > wants to write the env variable and value in one shot which would need
> > either a temporary buffer for value or a format specifier.
> > 
> > Fix these issues by adding a new printf format specifier, "%pOFm". With
> > the format specifier in place, simplify all the callers of
> > of_modalias(). of_modalias() can also be simplified with vsprintf()
> > being the only caller as it avoids the error conditions.
> 
> Shouldn't ACPI case also be considered? Otherwise we might see a deviation and
> then completely asynced variants of modalias based on different type of fwnode.

I don't understand what you are proposing. How the ACPI code and DT code 
generate the DT modalias are completely different already. Are you 
wanting to plumb a fwnode modalias op? We'd probably be better off with 
a printf op handler and moving much of the code out of lib/vsprintf.c.

Also, looks like the ACPI modalias code does kmallocs. Given the locking 
discussion, wouldn't that be problematic?

Rob