sound: Change PCMDIR_* numbering

[christos]

Summary

Needed by a follow-up patch, so that channels can be sorted properly.
This change does not affect the behavior of any subsystem.

Sponsored by: The FreeBSD Foundation
MFC after: 2 days

[dev_submerge.ch]

Could this be turned into an enum, to facilitate compiler checks in switch() statements? Or is there a policy on using enums in src? I see them far less often than I would expect.

[christos]

In D47198#1076392, @dev_submerge.ch wrote:

Could this be turned into an enum, to facilitate compiler checks in switch() statements? Or is there a policy on using enums in src? I see them far less often than I would expect.

My plan was to convert more examples like this to enums in a follow up patch, but I've got no objection at all to making it an enum here.

[christos]

Change to an enum.

[markj]

sys/dev/sound/pcm/channel.h

339

I would consider giving this one a non-zero value, so that invalid values that arise from zero-initialization are more obvious.

[christos]

Start from 1.

[markj]

Seems ok to me.

An anonymous enum type isn't terribly useful, you'd need to start defining variables using the new enum type in order to get checking in switch statements and so on. But, it doesn't hurt either.