notify_create (nr 509)

Create a notification file descriptor for inter-process signaling.

Signature

notify_create(flags: u32) → fd or -errno

Arguments

Arg	Register	Description
flags	rdi	Flags: `NOTIFY_CLOEXEC` (0x01) sets close-on-exec on the fd

Return value

On success, returns a file descriptor for the notification object.

Errors

Error	Condition
EINVAL	Unknown flags are set
EMFILE	Process fd table is full

Description

Creates a notification fd for signaling between processes. The fd is used with two operations:

Consumer: submits OP_RING_WAIT (opcode 7) via io_submit on the notification fd. The completion port blocks until the producer signals.
Producer: calls notify(fd) (syscall 510) to signal. If an OP_RING_WAIT is armed, a completion is posted to the consumer’s port.

The notification fd can be passed to child processes via inheritance (clone + execve) or via IPC fd-passing (ipc_send / ipc_recv).

Semantics

Edge-triggered, one-shot: one notify() produces one completion. The consumer must re-submit OP_RING_WAIT to receive the next signal.
Buffered: if notify() is called before OP_RING_WAIT is armed, the notification is buffered. The next OP_RING_WAIT completes immediately. Multiple pre-arm signals coalesce into one.
Single waiter: only one OP_RING_WAIT can be pending per fd.

Flags

Flag	Value	Description
`NOTIFY_CLOEXEC`	0x01	Set close-on-exec on the returned fd

Userspace usage (C)

#define SYS_NOTIFY_CREATE 509
#define NOTIFY_CLOEXEC    0x01

static long notify_create(unsigned int flags) {
    return syscall(SYS_NOTIFY_CREATE, flags);
}

int nfd = notify_create(0);

Implementation

osl/src/notify.rs — sys_notify_create

Backing struct: libkernel/src/notify.rs — NotifyInner

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