linux-kernel - Re: [PATCH v3 01/17] cmdline: Add generic function to build command line.

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Message-Id: <D8C1FBF6-E5C0-4233-BCB8-694274EA28F9@goldelico.com>
Date:   Tue, 30 Mar 2021 20:07:30 +0200
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Daniel Walker <danielwa@...co.com>,
        Christophe Leroy <christophe.leroy@...roup.eu>
Cc:     will@...nel.org, Rob Herring <robh@...nel.org>,
        daniel@...pelevich.san-francisco.ca.us, linux-arch@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        linuxppc-dev@...ts.ozlabs.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        microblaze <monstr@...str.eu>,
        linux-mips <linux-mips@...r.kernel.org>,
        nios2 <ley.foon.tan@...el.com>, openrisc@...ts.librecores.org,
        linux-hexagon@...r.kernel.org, linux-riscv@...ts.infradead.org,
        x86@...nel.org, linux-xtensa@...ux-xtensa.org,
        linux-sh@...r.kernel.org, sparclinux@...r.kernel.org
Subject: Re: [PATCH v3 01/17] cmdline: Add generic function to build command line.


> Am 30.03.2021 um 19:27 schrieb Daniel Walker <danielwa@...co.com>:
> 
> On Fri, Mar 26, 2021 at 01:44:48PM +0000, Christophe Leroy wrote:
>> This code provides architectures with a way to build command line
>> based on what is built in the kernel and what is handed over by the
>> bootloader, based on selected compile-time options.
>> 
>> Signed-off-by: Christophe Leroy <christophe.leroy@...roup.eu>
>> ---
>> v3:
>> - Addressed comments from Will
>> - Added capability to have src == dst
>> ---
>> include/linux/cmdline.h | 57 +++++++++++++++++++++++++++++++++++++++++
>> 1 file changed, 57 insertions(+)
>> create mode 100644 include/linux/cmdline.h
>> 
>> diff --git a/include/linux/cmdline.h b/include/linux/cmdline.h
>> new file mode 100644
>> index 000000000000..dea87edd41be
>> --- /dev/null
>> +++ b/include/linux/cmdline.h
>> @@ -0,0 +1,57 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef _LINUX_CMDLINE_H
>> +#define _LINUX_CMDLINE_H
>> +
>> +#include <linux/string.h>
>> +
>> +/* Allow architectures to override strlcat, powerpc can't use strings so early */
>> +#ifndef cmdline_strlcat
>> +#define cmdline_strlcat strlcat
>> +#endif
>> +
>> +/*
>> + * This function will append or prepend a builtin command line to the command
>> + * line provided by the bootloader. Kconfig options can be used to alter
>> + * the behavior of this builtin command line.
>> + * @dst: The destination of the final appended/prepended string.
>> + * @src: The starting string or NULL if there isn't one.
>> + * @len: the length of dest buffer.
>> + */
> 
> Append or prepend ? Cisco requires both at the same time. This is why my
> implementation provides both. I can't use this with both at once.

Just an idea: what about defining CMDLINE as a pattern where e.g. "$$" or "%%"
is replaced by the boot loader command line?

Then you can formulate replace, prepend, append, prepend+append with a single
CONFIG setting.

It may be a little more complex in code (scanning for the pattern and replacing
it and take care to temporary memory) but IMHO it could be worth to consider.

BR,
Nikolaus Schaller