pwritev

fn pwritev(
    ev: *Evented,
    cancel_region: *CancelRegion,
    fd: fd_t,
    iov: []const iovec_const,
    offset: ?u64,
) File.Writer.Error!usize {
    if (iov.len == 0) return 0;
    const scatter = iov.len > 1 or iov[0].len > 0xfffff000;
    while (true) {
        const thread = try cancel_region.awaitIoUring();
        thread.enqueue().* = .{
            .opcode = if (scatter) .WRITEV else .WRITE,
            .flags = 0,
            .ioprio = 0,
            .fd = fd,
            .off = offset orelse std.math.maxInt(u64),
            .addr = if (scatter) @intFromPtr(iov.ptr) else @intFromPtr(iov[0].base),
            .len = @intCast(if (scatter) iov.len else iov[0].len),
            .rw_flags = 0,
            .user_data = @intFromPtr(cancel_region.fiber),
            .buf_index = 0,
            .personality = 0,
            .splice_fd_in = 0,
            .addr3 = 0,
            .resv = 0,
        };
        ev.yield(null, .nothing);
        const completion = cancel_region.completion();
        switch (completion.errno()) {
            .SUCCESS => return @as(u32, @bitCast(completion.result)),
            .INTR, .CANCELED => {},
            .INVAL => |err| return errnoBug(err),
            .FAULT => |err| return errnoBug(err),
            .AGAIN => return error.WouldBlock,
            .BADF => return error.NotOpenForWriting, // Can be a race condition.
            .DESTADDRREQ => |err| return errnoBug(err), // `connect` was never called.
            .DQUOT => return error.DiskQuota,
            .FBIG => return error.FileTooBig,
            .IO => return error.InputOutput,
            .NOSPC => return error.NoSpaceLeft,
            .PERM => return error.PermissionDenied,
            .PIPE => return error.BrokenPipe,
            .CONNRESET => |err| return errnoBug(err), // Not a socket handle.
            .BUSY => return error.DeviceBusy,
            else => |err| return unexpectedErrno(err),
        }
    }
}