fileSeekTo

fn fileSeekTo(userdata: ?*anyopaque, file: File, offset: u64) File.SeekError!void {
    const t: *Threaded = @ptrCast(@alignCast(userdata));
    _ = t;

    if (is_windows) {
        var iosb: windows.IO_STATUS_BLOCK = undefined;
        var info: windows.FILE.POSITION_INFORMATION = .{ .CurrentByteOffset = @bitCast(offset) };
        const syscall: Syscall = try .start();
        while (true) switch (windows.ntdll.NtSetInformationFile(
            file.handle,
            &iosb,
            &info,
            @sizeOf(windows.FILE.POSITION_INFORMATION),
            .Position,
        )) {
            .SUCCESS => return syscall.finish(),
            .CANCELLED => try syscall.checkCancel(),
            .ACCESS_DENIED => return syscall.fail(error.AccessDenied),
            .PIPE_NOT_AVAILABLE => return syscall.fail(error.Unseekable),
            else => |status| return syscall.unexpectedNtstatus(status),
        };
    }

    if (native_os == .wasi and !builtin.link_libc) {
        const syscall: Syscall = try .start();
        while (true) {
            var new_offset: std.os.wasi.filesize_t = undefined;
            switch (std.os.wasi.fd_seek(file.handle, @bitCast(offset), .SET, &new_offset)) {
                .SUCCESS => {
                    syscall.finish();
                    return;
                },
                .INTR => {
                    try syscall.checkCancel();
                    continue;
                },
                else => |e| {
                    syscall.finish();
                    switch (e) {
                        .BADF => |err| return errnoBug(err), // File descriptor used after closed.
                        .INVAL => return error.Unseekable,
                        .OVERFLOW => return error.Unseekable,
                        .SPIPE => return error.Unseekable,
                        .NXIO => return error.Unseekable,
                        .NOTCAPABLE => return error.AccessDenied,
                        else => |err| return posix.unexpectedErrno(err),
                    }
                },
            }
        }
    }

    if (posix.SEEK == void) return error.Unseekable;

    return posixSeekTo(file.handle, offset);
}