Using snd_device_name_hint() with iface "card"

[MathisMARION]

Hello,

I have been experimenting with the alsa library, and I tried to use the snd_device_name_hint() function to print information about devices. It doesn't seem documented here so I looked up for examples online, and explored the source code as well.

Looking at the source code, it seems like the function should be able to take "card" as a valid interface. However when I run this function, it returns ENOENT. I ran my program with gdb and found that this call to add_card() was returning the error. add_card calls snd_config_search which loops through a list to find a match. In my case I found out that the list contained "cards" (with an s), while the code was searching for "card" so I am left wondering if this was done on purpose. Moreover I can get info about my sound cards using /proc/asound/cards (with an s again) so it makes me doubt even more...

I am running Ubuntu 20.04.5, and have installed libasound2-dev version 1.2.2-2.1ubuntu2.5. I can give more info about my setup if needed, I am just unsure what other info would help as of right now.

Here's a simple program reproducing my issue:

#include <alsa/asoundlib.h>
#include <stdio.h>

int main()
{
    void **hints;
    int ret;

    ret = snd_device_name_hint(-1, "card", &hints);
    if (ret) {
        printf("snd_device_name_hint: %s\n", snd_strerror(ret));
        return EXIT_FAILURE;
    }
    snd_device_name_free_hint(hints);
    return EXIT_SUCCESS;
}

snd_device_name_hint: No such file or directory

Putting "cards" instead results in EINVAL:

snd_device_name_hint: Invalid argument

[perexg]

It's rather a bug than feature. The EINVAL return code should be returned in this case, because 'card:' devices do not exist.

Fixes in 7e678d70c20e5d9f55b72ef0da6d8c0b38067b17 .

[perexg]

BTW: Use snd_card_next() and other snd_card functions to enumerate the ALSA cards. The procfs should not be used.