RFC: wg syncpeers wg0 wireguard.conf

[Jason A. Donenfeld]

Hey Lonnie,

I gave it a stab in this branch:
https://git.zx2c4.com/WireGuard/commit/?h=jd/syncconf Try it out and
let me know if it does what you had in mind?

One of the things that always goes wrong with "sync" algorithms in
software -- and the commit above at the moment is no exception -- is
that they're kind of racey. In order to synchronize, we have to read
the current state, compare it, and then set our new state. But in
between, the state could have changed out from underneath us. One
strategy for this is to just do nothing and put some notice in the man
page. Another strategy is to read back the result at the end, compare
it, and loop like this until we reach the stable state. This then
requires implementing some equality function.

The other thing I was wondering is: aside from performance and races
as described above, why not just make this the functionality of
`setconf`? Then there's be no need to introduce a new subcommand. In
otherwords, the idea would be to make `setconf` not destroy existing
peers if we're going to be re-adding them again.

Thoughts?

Jason