fileLength

fn fileLength(userdata: ?*anyopaque, file: File) File.LengthError!u64 {
    const ev: *Evented = @ptrCast(@alignCast(userdata));
    var cancel_region: CancelRegion = .init();
    defer cancel_region.deinit();
    while (true) {
        var statx_buf = std.mem.zeroes(linux.Statx);
        const thread = try cancel_region.awaitIoUring();
        thread.enqueue().* = .{
            .opcode = .STATX,
            .flags = 0,
            .ioprio = 0,
            .fd = file.handle,
            .off = @intFromPtr(&statx_buf),
            .addr = @intFromPtr(""),
            .len = @bitCast(linux.STATX{ .SIZE = true }),
            .rw_flags = linux.AT.EMPTY_PATH,
            .user_data = @intFromPtr(cancel_region.fiber),
            .buf_index = 0,
            .personality = 0,
            .splice_fd_in = 0,
            .addr3 = 0,
            .resv = 0,
        };
        ev.yield(null, .nothing);
        switch (cancel_region.errno()) {
            .SUCCESS => {
                if (!statx_buf.mask.SIZE) return error.Unexpected;
                return statx_buf.size;
            },
            .INTR, .CANCELED => {},
            .ACCES => |err| return errnoBug(err),
            .BADF => |err| return errnoBug(err), // File descriptor used after closed.
            .FAULT => |err| return errnoBug(err),
            .INVAL => |err| return errnoBug(err),
            .LOOP => |err| return errnoBug(err),
            .NAMETOOLONG => |err| return errnoBug(err),
            .NOENT => |err| return errnoBug(err),
            .NOMEM => return error.SystemResources,
            .NOTDIR => |err| return errnoBug(err),
            else => |err| return unexpectedErrno(err),
        }
    }
}