linux-kernel - Re: [PATCH 01/99] lib: Add option iterator

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Date:   Tue, 7 Mar 2023 09:40:48 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Randy Dunlap <rdunlap@...radead.org>, deller@....de,
        paulus@...ba.org, benh@...nel.crashing.org, linux@...linux.org.uk,
        pjones@...hat.com, timur@...nel.org, adaplas@...il.com,
        s.hauer@...gutronix.de, shawnguo@...nel.org, mbroemme@...mpq.org,
        thomas@...ischhofer.net, James.Bottomley@...senPartnership.com,
        spock@...too.org, sudipm.mukherjee@...il.com,
        teddy.wang@...iconmotion.com, geert+renesas@...der.be,
        corbet@....net
Cc:     linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 01/99] lib: Add option iterator

Hi

Am 06.03.23 um 23:37 schrieb Randy Dunlap:
[...]
>> + *
>> + * The call to option_iter_init() initializes the iterator instance
>> + * from the option string. The while loop walks over the individual
>> + * options in the sting and returns each in the second argument. The
>> + * returned memory is owned by the iterator instance and callers may
>> + * not modify or free it. The call to option_iter_release() frees all
>> + * resources of the iterator. This process does not modify the original
>> + * option string. If the option string contains an empty option (i.e.,
>> + * two commas next to each other), option_iter_next() skips the empty
>> + * option automatically.
> 
> Is that latter skipping over a ",," automatically something that you have
> observed as needed?

It's not strictly needed for correctness, but many of those fbdev 
drivers contain code to do that. Like this one:

 
https://elixir.bootlin.com/linux/v6.2/source/drivers/video/fbdev/vesafb.c#L217

So doing it in the _incr() helper seems useful

> I can imagine a driver or module wanting to know that an empty string
> was entered (i.e., ",,").

I only looked at fbdev drivers, but none of them cared about empty 
strings. They all have named options and/or key-value pairs.

> 
>> + */
>> +
>> +/**
>> + * option_iter_init - Initializes an option iterator
>> + * @iter:	the iterator to initialize
>> + * @options:	the options string
>> + */
>> +void option_iter_init(struct option_iter *iter, const char *options)
>> +{
>> +	if (options && *options)
>> +		iter->optbuf = kstrdup(options, GFP_KERNEL); // can be NULL
>> +	else
>> +		iter->optbuf = NULL;
>> +	iter->next_opt = iter->optbuf;
>> +}
>> +EXPORT_SYMBOL(option_iter_init);
>> +
>> +/**
>> + * option_iter_release - Releases an option iterator's resources
>> + * @iter:	the iterator
>> + */
>> +void option_iter_release(struct option_iter *iter)
>> +{
>> +	kfree(iter->optbuf);
>> +	iter->next_opt = NULL;
>> +}
>> +EXPORT_SYMBOL(option_iter_release);
>> +
>> +/**
>> + * option_iter_incr - Return current option and advance to the next
>> + * @iter:	the iterator
>> + *
>> + * Returns:
> 
>   * Return:
> matches kernel-doc notation documentation.
> 
>> + * The current option string, or NULL if there are no more options.
>> + */
>> +const char *option_iter_incr(struct option_iter *iter)
>> +{
>> +	char *opt;
>> +
>> +	if (!iter->next_opt) { // can be OK if kstrdup failed
>> +		if (iter->optbuf) // iter has already been released; logic error
>> +			pr_err("Incrementing option iterator without string\n");
>> +		return NULL;
>> +	}
>> +
>> +	do {
>> +		opt = strsep(&iter->next_opt, ",");
>> +		if (!opt)
>> +			return NULL;
>> +	} while (!*opt); // found empty option string, try next
>> +
>> +	return opt;
>> +}
>> +EXPORT_SYMBOL(option_iter_incr);
> 
> Looks useful. Thanks.

Thanks.

Best regards
Thomas

> 

-- 
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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