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

> Indeed. One word is *exactly* what a normal system call returns too.
>
> That said, normally we have a user-space library layer to turn that into
> the "errno + return value" thing, and in the case of async() calls we
> very basically wouldn't have that. So either:
>
> - we'd need to do it in the kernel (which is actually nasty, since
> different system calls have slightly different semantics - some don't
> return any error value at all, and negative numbers are real numbers)
>
> - we'd have to teach user space about the "negative errno" mechanism, in
> which case one word really is alwats enough.
>
> Quite frankly, I much prefer the second alternative. The "negative errno"
> thing has not only worked really really well inside the kernel, it's so
> obviously 100% superior to the standard UNIX "-1 + errno" approach that
> it's not even funny.

Currently it's in the syscall wrapper. Couldn't we have it in the
asys_teardown_stack() stub?



> 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).



- Davide


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