linux-kernel - Re: [PATCH v2 001/101] lib: Add option iterator

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Message-ID: <194d943e-e840-2941-22b9-f6a1a096c539@suse.de>
Date:   Fri, 10 Mar 2023 13:38:24 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:     deller@....de, timur@...nel.org, rdunlap@...radead.org,
        paulus@...ba.org, benh@...nel.crashing.org, linux@...linux.org.uk,
        pjones@...hat.com, adaplas@...il.com, s.hauer@...gutronix.de,
        shawnguo@...nel.org, mbroemme@...mpq.org, thomas@...ischhofer.net,
        James.Bottomley@...senpartnership.com, sudipm.mukherjee@...il.com,
        teddy.wang@...iconmotion.com, corbet@....net,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 001/101] lib: Add option iterator

Hi

Am 10.03.23 um 09:21 schrieb Geert Uytterhoeven:
> Hi Thomas,
> 
> On Thu, Mar 9, 2023 at 5:02 PM Thomas Zimmermann <tzimmermann@...e.de> wrote:
>> Add struct option_iter and helpers that walk over individual options
>> of an option string. Add documentation.
>>
>> Kernel parameters often have the format of
>>
>>    param=opt1,opt2:val,opt3
>>
>> where the option string contains a number of comma-separated options.
>> Drivers usually use strsep() in a loop to extract individual options
>> from the string. Each call to strsep() modifies the given string, so
>> callers have to duplicate kernel parameters that are to be parsed
>> multiple times.
>>
>> The new struct option_iter and its helpers wrap this code behind a
>> clean interface. Drivers can iterate over the options without having
>> to know the details of the option-string format. The iterator handles
>> string memory internally without modifying the original options.
>>
>> v2:
>>          * improve documentation (Randy)
>>          * implement option_iter_next() as function
>>          * allow modification of the returned options
>>
>> Signed-off-by: Thomas Zimmermann <tzimmermann@...e.de>
> 
> Thanks for your patch!
> 
> I> ---
>>   Documentation/core-api/kernel-api.rst |   9 +++
>>   include/linux/cmdline.h               |  36 +++++++++
>>   lib/Makefile                          |   2 +-
>>   lib/cmdline_iter.c                    | 109 ++++++++++++++++++++++++++
>>   4 files changed, 155 insertions(+), 1 deletion(-)
>>   create mode 100644 include/linux/cmdline.h
>>   create mode 100644 lib/cmdline_iter.c
> 
> Just wondering, is there any code that can be shared with/reused from
> the existing lib/cmdline.c?

AFAIU, cmdline.o is linked into early-boot code, which prevents it from 
using dynamic memory allocation, such as kstrdup() and kfree(). The 
linker warns about this:

   LD      arch/x86/boot/compressed/vmlinux
   ld: arch/x86/boot/compressed/kaslr.o: in function `get_option':
   kaslr.c:(.text+0x532): undefined reference to `kstrdup'
   ld: arch/x86/boot/compressed/vmlinux: hidden symbol `kstrdup' isn't
	defined
   ld: final link failed: bad value

So the iterator is in a separate source file.

The code in cmdline.c mostly deals with parsing individual values or 
key-value pairs. Nothing moves over the complete string and returns 
options one by one. There's not much to share AFAICT.

Best regards
Thomas


> 
> Gr{oetje,eeting}s,
> 
>                          Geert
> 

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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