io_wait (nr 503)

Wait for completions on a completion port.

Signature

io_wait(port_fd: i32, completions_ptr: *mut IoCompletion, max: u32, min: u32, timeout_ns: u64) → count or -errno

Arguments

Arg	Register	Description
port_fd	rdi	Completion port fd
completions_ptr	rsi	User buffer for completion entries
max	rdx	Maximum completions to return
min	r10	Minimum completions before returning (0 = non-blocking poll)
timeout_ns	r8	Timeout in nanoseconds (0 = wait forever)

Completion entry layout

struct IoCompletion {       // 24 bytes, repr(C)
    uint64_t user_data;     // Copied from submission
    int64_t  result;        // Bytes transferred, or negative errno
    uint32_t flags;         // Reserved
    uint32_t opcode;        // Operation that completed
};

Return value

On success, returns the number of completions written to completions_ptr (between 0 and max).

Errors

Error	Condition
EFAULT	`completions_ptr` is invalid
EBADF	`port_fd` is not a valid completion port

Description

Blocks the calling thread until at least min completions are available on the port, or the timeout expires. Drains up to max completions and copies them to user memory.

For OP_READ completions, the kernel buffer containing read data is copied to the user-space destination address that was specified in the original submission.

For OP_IPC_RECV completions, transferred file descriptors are installed in the receiver’s fd table and the IpcMessage.fds array is rewritten with the new fd numbers before copying to user memory.

The timeout is implemented as a cancellable async timer task. A timeout of 0 means wait forever (no timeout).

Implementation

osl/src/io_port.rs — sys_io_wait

ostoo