//! The device-manager protocol (docs/device-manager.md): what drivers and
//! applications say to the device manager over its well-known endpoint. The
//! vfs-protocol pattern — extern-struct messages, a version in the handshake,
//! reserved fields — so both sides depend on the contract by name. Deliberately
//! contains nothing lifecycle-shaped: stopping, liveness (the zero-length ping),
//! and exit reasons are the universal vocabulary of
//! docs/process-lifecycle.md, not this protocol.

/// The protocol version a driver states in its hello. A manager that cannot
/// serve a driver's version refuses the hello, and the mismatch is loud at
/// startup instead of quiet corruption later.
pub const version: u16 = 1;

/// What kind of driver is talking (docs/driver-model.md's shapes).
pub const Role = enum(u8) {
    /// Owns a controller and reports the devices behind it (`child_added`).
    bus = 1,
    /// Serves one device, reached through a bus's transfer protocol.
    device = 2,
};

/// The message kinds. `child_added`/`child_removed` land in M18.2;
/// `enumerate`/`subscribe` in M18.3.
pub const Operation = enum(u8) {
    hello = 1,
};

/// `Hello.device_id` for a driver that serves no enumerated device (a test
/// fixture, a synthetic source).
pub const no_device: u64 = ~@as(u64, 0);

/// The handshake, sent once by every driver the manager spawns — the manager's
/// one self-enforced deadline: spawned and silent past it means wrong binary,
/// wrong version, or wedged before main, and the stop sequence follows.
pub const Hello = extern struct {
    operation: u8 = @intFromEnum(Operation.hello),
    /// A Role value.
    role: u8,
    /// The protocol version this driver was built against (`version`).
    version: u16 = version,
    reserved: u32 = 0,
    /// The device this driver was assigned (its argv[1]), or `no_device`.
    device_id: u64,
};

pub const hello_size = @sizeOf(Hello);

/// The manager's answer to a hello. Nonzero status = refused (version mismatch,
/// unknown sender); a refused driver should exit cleanly.
pub const HelloReply = extern struct {
    status: i32,
    reserved: u32 = 0,
};

pub const reply_size = @sizeOf(HelloReply);

/// Upper bound on any message in this protocol — sizes the endpoint buffers.
pub const message_maximum = 64;