Re: [PATCHv2 1/1] Documentation: describe how to add a system call

[josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org]

On Fri, Jul 31, 2015 at 02:19:29PM -0700, Andy Lutomirski wrote:
> On Fri, Jul 31, 2015 at 1:59 PM,  <josh-iaAMLnmF4UmaiuxdJuQwMA@public.gmane.org> wrote:
> > Agreed.  I think the proposal above would be a net improvement, but
> > ideally you'd want something that's annotated and generates automatic
> > marshalling code.
> >
> 
> I assume this is idle musing.  If, however, we were to actually do
> this, I'd suggest we seriously consider speaking the Cap'n Proto
> serialization format.  It's quite nice, it encodes and decodes *very*
> quickly and, unlike TLV schemes, you don't have to read it in order,
> making the read-side code less awkward.

That seems like *massive* overkill for a kernel<->userspace syscall
interface.  I was more thinking about having a few standardized marshal
types, and incrementally adding more when more patterns show up.  For a
first pass, just automatically running copy_from_user and
copy_param_struct on appropriate sets of __user parameters identified as
such in a structured text file seems quite sufficient.  (Plus
automatically generating syscalls.h from that.)