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SubjectRe: [PATCH v2 001/101] lib: Add option iterator
From
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@suse.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@suse.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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