mixer(3): Implement mixer_get_path() function

[christos]

Summary

This is better than hardcoding device paths in mixer applications.

Sponsored by: The FreeBSD Foundation
MFC after: 1 day

[dev_submerge.ch]

lib/libmixer/mixer.c

503

With this check buffer size can still be insufficient to hold BASEPATH + unit + '\0'. We should return an error in that case. Maybe check after strlcpy() and sndprintf()?

[christos]

lib/libmixer/mixer.c

503

It will be insufficient indeed. I added this to make sure it *at least* fits "/dev/mixer". We could bump this to something like BASEPATH + 3 (are we gonna have more than 3-digit units) +'\0'.

[dev_submerge.ch]

lib/libmixer/mixer.c

503

I think there's an upper limit to the possible number of pcm devices somewhere, but I'd suggest to check the return values of strlcpy() and snprintf() instead. That's what they are there for.

[christos]

Address Florian's comments.

[christos]

Mention EXAMPLES section in mixer_get_nmixers().