Gate

Gates provide a rendezvous point for Contexts (and optionally Interrupts) using IPC.

Branding

Gate key brands separate Gate keys into two groups: service keys and transparent keys (or client keys). The two groups are distinguished by the MSB of the brand (set for transparent, clear for service).

Only service keys have access to the methods described below. Any invocations on a transparent key flow right through the Gate to any Context receiving on the far side (using a service key).

Service Keys

Service keys have the top bit clear. Programs holding a service key can invoke the methods described below.

Remaining bits in the service key brand are reserved and should be zero. That is, in the version described by this manual, the only valid service key brand is Brand(1) << 63.

Programs can receive from a Gate service key, which will rendezvous with another program sending through a transparent key, blocking if necessary. Because the sender is always using a transparent key, any message received in this way will have the top bit of the sender brand set.

Transparent Keys

Transparent keys have the top bit set. The brand is passed, otherwise uninterpreted, to a program using a receive IPC on a service key.

Methods

Make Client Key (1)

Derives a transparent (client) key for this gate with the given brand. The brand must be a valid brand for a transparent key — that is, it must have its MSB set.

This operation is intended for servers that want to distribute identifiable keys to different clients.

Call

• d0: brand low 32 bits.
• d1: brand high 32 bits.

Reply

• k1: derived key.

Exceptions

• k.bad_argument if the given brand does not have its MSB set.