wg: Improve wg_peer_alloc() to simplify the calling

[kevans]

Summary

Move the necessary extra logics (i.e., noise_remote_enable() and
TAILQ_INSERT_TAIL()) from wg_ioctl_set() to wg_peer_alloc(), and thus
make it easier to be called. Actually, the updated version is more
asymmetric to wg_peer_destroy() and thus less likely to be misused.
Meanwhile, rename it to wg_peer_create() to look more consistent with
wg_peer_destroy().

Obtained from: DragonflyBSD

[kevans]

Replaces D46670; I've set the author to this one to Aaron as I've only made two very minor tweaks from what appears in DragonflyBSD:

• We return ENOSPC if wg_peer_create() failed, since all of the allocations are M_WAITOK... this is perhaps a bit ugly
• Retained the need_insert notion, renamed it to need_cleanup... I went for the minimally invasive change, haven't looked at the rest of the diff from DragonflyBSD.

[aly_aaronly.me]

In D49796#1135140, @kevans wrote:

Replaces D46670; I've set the author to this one to Aaron as I've only made two very minor tweaks from what appears in DragonflyBSD:

Thank you very much.

• We return ENOSPC if wg_peer_create() failed, since all of the allocations are M_WAITOK... this is perhaps a bit ugly

Yah, I now see it; was unaware of this.

• Retained the need_insert notion, renamed it to need_cleanup... I went for the minimally invasive change, haven't looked at the rest of the diff from DragonflyBSD.

I decided to be lazy and not to clean the new but unconfigured peer (e.g., invalid sockaddr, aip failure), because the user would retry to configure the peer.

sys/dev/wg/if_wg.c

393

Need to add noise_remote_free(peer->p_remote, NULL) before free(). I missed this in DragonFly; will fix it later.

2429

The comment is inaccurate. I suggest "wg_peer_create() can only fail because noise_remote_enable() failed and can only return ENOSPC".

Hmm, I think it maybe better to change it to:

static struct wg_peer *
wg_peer_create(struct wg_softc *sc, const uint8_t pub_key[WG_KEY_SIZE], int *errp);

I personally prefer it over int wg_peer_create(struct wg_peer **peerp, ...).

[kevans]

Address review feedback:

• Free p_remote if we failed to enable it
• Propagate the error from noise_remote_enable() more explicitly

Commit message locally is updated to note the actual DragonflyBSD commit in the
Obtained from: line and also to note that it's (with some changes).

[aly_aaronly.me]

Cool. I'll also tweak wg_peer_create() in DragonFly to propagate the error. Thank you.

[kevans]

Committed as 7121e9414f29; missed the tag.