danos/library/runtime/ipc.zig

//! User-space IPC helpers over the kernel's synchronous IPC syscalls. A client
//! `call`s an endpoint (send + block for reply); the VFS server and drivers are
//! reached this way. The server side (`replyWait`, which returns two values) is
//! added with the first server binary.

const abi = @import("abi");
const sc = @import("system-call.zig");

/// A small-int handle into the calling process's handle table.
pub const Handle = usize;

/// A fixed-size, register-friendly message payload. Server protocols (VFS, driver)
/// layer their own wire format on top of the bytes a call carries.
pub const Message = extern struct {
    tag: u64 = 0,
    a: u64 = 0,
    b: u64 = 0,
    c: u64 = 0,
};

/// Whether a system_call return value is a wrapped -errno (lands in the top page).
inline fn failed(r: usize) bool {
    return r > ~@as(usize, 0) - 4095;
}

/// Create a new endpoint owned by this process; returns its handle.
pub fn createIpcEndpoint() ?Handle {
    const r = sc.systemCall0(.create_ipc_endpoint);
    return if (failed(r)) null else r;
}

/// Publish endpoint `h` under a well-known service id so other processes find it.
pub fn register(id: abi.ServiceId, h: Handle) bool {
    return !failed(sc.systemCall2(.ipc_register, @intFromEnum(id), h));
}

/// Find the endpoint published under `id`, installing a handle to it in this
/// process.
pub fn lookup(id: abi.ServiceId) ?Handle {
    const r = sc.systemCall1(.ipc_lookup, @intFromEnum(id));
    return if (failed(r)) null else r;
}

pub const CallError = error{Failed};

/// The result of a capability-passing `callCap`: the reply length, and the handle of
/// an endpoint the server sent back (e.g. a per-device channel), or null.
pub const Reply = struct {
    len: usize,
    cap: ?Handle,
};

/// Send `message` to endpoint `h` and block until the server replies into `reply`,
/// optionally handing the server a capability (`send_cap`) and receiving one back.
/// This is the class-driver "open" primitive: call a bus with `send_cap = null`, get a
/// private per-device endpoint back in `.cap`. Two return values (reply length in rax,
/// received handle in r8) need a hand-written stub — r8 is read-write (in: reply
/// capacity, arg #4; out: the received handle).
pub fn callCap(h: Handle, message: []const u8, reply: []u8, send_cap: ?Handle) CallError!Reply {
    var rax: usize = undefined;
    var r8: usize = reply.len; // in: reply capacity (arg #4); out: received capability handle
    asm volatile ("syscall"
        : [rax] "={rax}" (rax),
          [r8] "+{r8}" (r8),
        : [n] "{rax}" (@intFromEnum(abi.SystemCall.ipc_call)),
          [a0] "{rdi}" (h),
          [a1] "{rsi}" (@intFromPtr(message.ptr)),
          [a2] "{rdx}" (message.len),
          [a3] "{r10}" (@intFromPtr(reply.ptr)),
          [a5] "{r9}" (send_cap orelse abi.no_cap),
        : .{ .rcx = true, .r11 = true, .memory = true });
    if (failed(rax)) return error.Failed;
    return .{ .len = rax, .cap = if (r8 == abi.no_cap) null else r8 };
}

/// Send `message` to endpoint `h` and block until the server replies into `reply`.
/// Returns the reply length. The common case: no capability passed either way.
pub fn call(h: Handle, message: []const u8, reply: []u8) CallError!usize {
    return (try callCap(h, message, reply, null)).len;
}

/// Post `message` to endpoint `h`'s asynchronous queue and return immediately — no
/// rendezvous, no reply, no blocking. The receiver picks it up through `replyWait` as a
/// buffered message (`Received.isMessage`). Unlike `call`, this **cannot hang on a dead
/// or slow peer**, which is why a broadcaster (the input service) delivers events this
/// way. The payload must fit an endpoint slot (64 bytes); a full queue drops the oldest
/// message. Returns false on failure (bad handle, oversized payload, bad buffer).
pub fn send(h: Handle, message: []const u8) bool {
    return !failed(sc.systemCall3(.ipc_send, h, @intFromPtr(message.ptr), message.len));
}

/// Set in `Received.badge` when what arrived is an asynchronous notification — a
/// bound device interrupt — rather than a client's message. The low bits carry the
/// GSI. See `isNotification`.
pub const notify_badge_bit: u64 = abi.notify_badge_bit;

/// Set alongside `notify_badge_bit` when the notification is a **child-exit
/// notice** — a process this one spawned (with an exit endpoint) has ended —
/// rather than a device interrupt. The low bits carry the child's process id.
pub const notify_exit_bit: u64 = abi.notify_exit_bit;

/// Set alongside `notify_badge_bit` when the wake-up is a **buffered message** — a payload
/// posted with `send` (`ipc_send`) — rather than a bare device interrupt or child-exit
/// notice. The payload is in the `replyWait` receive buffer (`Received.len` bytes); the
/// low bits of the badge carry the sender's task id. See `Received.isMessage`.
pub const notify_message_bit: u64 = abi.notify_message_bit;

/// The result of a `replyWait`: the request length, the sender's badge (a task id, or
/// an IRQ notification if the high bit is set), and any capability the request carried.
pub const Received = struct {
    len: usize,
    badge: u64,
    cap: ?Handle,

    /// True if this wake-up was an asynchronous notification (a device interrupt
    /// or a child-exit notice), not a client request. An event loop branches on
    /// this; there is no reply owed on the notification path.
    pub fn isNotification(self: Received) bool {
        return self.badge & notify_badge_bit != 0;
    }

    /// True if this wake-up tells of a supervised child's end — the notification
    /// requested by passing an exit endpoint to `system.spawnSupervised`.
    pub fn isChildExit(self: Received) bool {
        return self.isNotification() and self.badge & notify_exit_bit != 0;
    }

    /// True if this wake-up is a **buffered message** posted with `send` (`ipc_send`):
    /// there is a payload in the receive buffer (`self.len` bytes) and no reply is owed.
    /// The subscriber side of a broadcast branches on this.
    pub fn isMessage(self: Received) bool {
        return self.isNotification() and self.badge & notify_message_bit != 0;
    }

    /// The task id of whoever posted a buffered message, meaningful only when
    /// `isMessage`. (The badge's low bits, with the three high marker bits masked off.)
    pub fn senderTaskId(self: Received) u32 {
        return @intCast(self.badge & ~(notify_badge_bit | notify_exit_bit | notify_message_bit));
    }

    /// The interrupt source (a GSI), meaningful only when `isNotification` and
    /// not `isChildExit`.
    pub fn source(self: Received) u64 {
        return self.badge & ~notify_badge_bit;
    }

    /// The ended child's process id, meaningful only when `isChildExit`.
    pub fn childProcessId(self: Received) u32 {
        return @intCast(self.badge & ~(notify_badge_bit | notify_exit_bit));
    }
};

/// Server side of IPC_ReplyWait: deliver `reply` to the client last received (if any,
/// optionally handing it `send_cap`), then block until the next request arrives in
/// `receive`. Returns its length, the sender badge, and any capability the request
/// carried (in `.cap`). Three return values — length in rax, badge in rdx, received
/// handle in r8 — so it needs a hand-written stub: rdx is read-write (in: reply length,
/// arg #3; out: badge) and r8 is read-write (in: receive capacity, arg #4; out: handle).
pub fn replyWait(h: Handle, reply: []const u8, receive: []u8, send_cap: ?Handle) Received {
    var rax: usize = undefined;
    var rdx: usize = reply.len; // in: reply_len (arg #3); out: badge
    var r8: usize = receive.len; // in: receive capacity (arg #4); out: received capability handle
    asm volatile ("syscall"
        : [rax] "={rax}" (rax),
          [rdx] "+{rdx}" (rdx),
          [r8] "+{r8}" (r8),
        : [n] "{rax}" (@intFromEnum(abi.SystemCall.ipc_reply_wait)),
          [a0] "{rdi}" (h),
          [a1] "{rsi}" (@intFromPtr(reply.ptr)),
          [a3] "{r10}" (@intFromPtr(receive.ptr)),
          [a5] "{r9}" (send_cap orelse abi.no_cap),
        : .{ .rcx = true, .r11 = true, .memory = true });
    return .{ .len = rax, .badge = rdx, .cap = if (r8 == abi.no_cap) null else r8 };
}