hash(9): introduce hashalloc()/hashfree() KPI

[glebius]

Summary

This is a more extendable version than traditional hashinit(9). It allows
different kinds of slot headers with optional locks.

Implement traditional hashinit()/hashdestroy() on top of it.

[glebius]

Last minute change before sharing of course had a small mistake :)

[gallatin]

This is really clever. What about other lock types (rm / rms, sx, etc)?

[glebius]

I'll see if rmlock(9) and sx(9) can be added and update.

[imp]

Do you need to validate the enum value is know?

Can the lock and list types be automatically detected with _Generic somehow?

[glebius]

In D55904#1279057, @imp wrote:

Do you need to validate the enum value is know?

Do you mean if somebody passes a numeric instead of one of enum values? I think our compiler flags will forbid that.

Can the lock and list types be automatically detected with _Generic somehow?

I don't see a way to use _Generic facing outside of the KPI. It might be possible to make some use of it internally, I'll look into that.

[glebius]

Add sx(9) and rmlock(9) support.

[imp]

In D55904#1279059, @glebius wrote:

In D55904#1279057, @imp wrote:

Do you need to validate the enum value is know?

Do you mean if somebody passes a numeric instead of one of enum values? I think our compiler flags will forbid that.

I'm thinking default: would make sure.

Can the lock and list types be automatically detected with _Generic somehow?

I don't see a way to use _Generic facing outside of the KPI. It might be possible to make some use of it internally, I'll look into that.

Sure.

[glebius]

Some additions to the manual page.