[alsa-devel] RFC: add possibility to change text identification string

[Takashi Iwai]

At Tue, 11 Nov 2008 17:00:41 +0100 (CET),
Jaroslav Kysela wrote:
> 
> Hi all,
> 
> 	based on discussion today, I prepared a patch to handle udev-style 
> card renaming. Comments are welcome.

Looks good to me.  The sanity check of the id string should be used
for the assignment from the module option, too.

I first thought of making id module parameter writable.  But, this would
require more works, and needs to patch allover places.


One another solution regarding udev thingy is to accept a path as a
card number/index in alsa-lib.  When the card begins with '/', it's handled
as a path, for example.  Then, you can simply open that file instead of
parsing the whole snd_card_get_index(), etc.

This is a bit hacikish, so I'm not fully convinced, though.  Just an idea
make the things without changing the kernel infrastructure.



thanks,

Takashi



> 
> 					Jaroslav
> 
> >From b0dca2c114f465a11f1595854090a85f58870b35 Mon Sep 17 00:00:00 2001
> From: Jaroslav Kysela <perex at perex.cz>
> Date: Tue, 11 Nov 2008 16:51:02 +0100
> Subject: [PATCH] ALSA: add /sys/class/sound/card#/id (r/w) and card#/number (r/o) files
> 
> For udev, we need a way to rename soundcard names. The soundcard numbers
> (indexes) are hardwired but we have a text identification which can be
> changed at run-time. The ALSA user space tools already allow using of
> this text identification.
> 
> Signed-off-by: Jaroslav Kysela <perex at perex.cz>
> ---
>  sound/core/init.c |   66 ++++++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 65 insertions(+), 1 deletions(-)
> 
> diff --git a/sound/core/init.c b/sound/core/init.c
> index b47ff8b..1426abd 100644
> --- a/sound/core/init.c
> +++ b/sound/core/init.c
> @@ -533,6 +533,64 @@ static void choose_default_id(struct snd_card *card)
>  	}
>  }
>  
> +#ifndef CONFIG_SYSFS_DEPRECATED
> +static ssize_t
> +card_id_show_attr(struct device *dev,
> +		  struct device_attribute *attr, char *buf)
> +{
> +	struct snd_card *card = dev_get_drvdata(dev);
> +	return snprintf(buf, PAGE_SIZE, "%s\n", card ? card->id : "(null)");
> +}
> +
> +static ssize_t
> +card_id_store_attr(struct device *dev, struct device_attribute *attr,
> +		   const char *buf, size_t count)
> +{
> +	struct snd_card *card = dev_get_drvdata(dev);
> +	char buf1[sizeof(card->id)];
> +	size_t copy = count > sizeof(card->id) - 1 ?
> +					sizeof(card->id) - 1 : count;
> +	size_t idx;
> +	int c;
> +
> +	for (idx = 0; idx < copy; idx++) {
> +		c = buf[idx];
> +		if (!isalnum(c) && c != '_' && c != '-')
> +			return -EINVAL;
> +	}
> +	memcpy(buf1, buf, copy);
> +	buf1[copy] = '\0';
> +	mutex_lock(&snd_card_mutex);
> +	if (!snd_info_check_reserved_words(buf1)) {
> +	     __exist:
> +		mutex_unlock(&snd_card_mutex);
> +		return -EEXIST;
> +	}
> +	for (idx = 0; idx < snd_ecards_limit; idx++) {
> +		if (snd_cards[idx] && !strcmp(snd_cards[idx]->id, buf1))
> +			goto __exist;
> +	}
> +	strcpy(card->id, buf1);
> +	mutex_unlock(&snd_card_mutex);
> +
> +	return count;
> +}
> +
> +static struct device_attribute card_id_attrs =
> +	__ATTR(id, S_IRUGO | S_IWUSR, card_id_show_attr, card_id_store_attr);
> +
> +static ssize_t
> +card_number_show_attr(struct device *dev,
> +		     struct device_attribute *attr, char *buf)
> +{
> +	struct snd_card *card = dev_get_drvdata(dev);
> +	return snprintf(buf, PAGE_SIZE, "%i\n", card ? card->number : -1);
> +}
> +
> +static struct device_attribute card_number_attrs =
> +	__ATTR(number, S_IRUGO, card_number_show_attr, NULL);
> +#endif /* CONFIG_SYSFS_DEPRECATED */
> +
>  /**
>   *  snd_card_register - register the soundcard
>   *  @card: soundcard structure
> @@ -553,7 +611,7 @@ int snd_card_register(struct snd_card *card)
>  #ifndef CONFIG_SYSFS_DEPRECATED
>  	if (!card->card_dev) {
>  		card->card_dev = device_create(sound_class, card->dev,
> -					       MKDEV(0, 0), NULL,
> +					       MKDEV(0, 0), card,
>  					       "card%i", card->number);
>  		if (IS_ERR(card->card_dev))
>  			card->card_dev = NULL;
> @@ -576,6 +634,12 @@ int snd_card_register(struct snd_card *card)
>  	if (snd_mixer_oss_notify_callback)
>  		snd_mixer_oss_notify_callback(card, SND_MIXER_OSS_NOTIFY_REGISTER);
>  #endif
> +#ifndef CONFIG_SYSFS_DEPRECATED
> +	if (card->card_dev) {
> +		device_create_file(card->card_dev, &card_id_attrs);
> +		device_create_file(card->card_dev, &card_number_attrs);
> +	}
> +#endif
>  	return 0;
>  }
>  
> -- 
> 1.6.0.1.217.gb4928
> 
> 
> -----
> Jaroslav Kysela <perex at perex.cz>
> Linux Kernel Sound Maintainer
> ALSA Project, Red Hat, Inc.
> 
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