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SubjectRe: [PATCH 2 of 4] Introduce i386 fibril scheduling
On Mon, 5 Feb 2007, Kent Overstreet wrote:

> > > HOWEVER, they get returned differently. The cookie gets returned
> > > immediately, the system call result gets returned in-memory only after the
> > > async thing has actually completed.
> > >
> > > I would actually argue that it's not the kernel that should generate any
> > > cookie, but that user-space should *pass*in* the cookie it wants to, and
> > > the kernel should consider it a pointer to a 64-bit entity which is the
> > > return code.
> >
> > Yes. Let's have the userspace to "mark" the async operation. IMO the
> > cookie should be something transparent to the kernel.
> > Like you said though, that'd require compat-code (unless we fix the size).
>
> You don't need an explicit cookie if you're passing in a pointer to
> the return code, it doesn't really save you anything to do so. Say
> you've got a bunch of user threads (with or without stacks, it doesn't
> matter).
>
> struct asys_ret {
> int ret;
> struct thread *p;
> };
>
> struct asys_ret r;
> r.p = me;
>
> async_read(fd, buf, nbytes, &r);

Hmm, are you working for Symbian? Because that's exactly how they track
pending async operations (address of a status variable - wrapped in a
class of course, being them) ;)
That's another way of doing it, IMO no better no worse than letting
explicit cookie selection from userspace. You still have to have the
compat code though, either ways.



- Davide


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