Re: [PATCH] compatibility syscall layer (lets try again)

[george anzinger <george@mvista.com>]

Linus Torvalds wrote:
> 
> On Wed, 4 Dec 2002, george anzinger wrote:
> >
> > Once it changes the system call (eax, right), could the new
> > call code then just get the parms from the restart_block.
> 
> Agreed.
> 
> > I think it would be best to keep this as generic as
> > possible, i.e. let the new call code fetch its own
> > paramerers from the restart_block.
> 
> We could even have one _single_ a generic "restart" system call, and have
> the function pointer for that be in the restart block.

I think what you mean is that, if there is a
restart_function (i.e. the block is set up) and the return
is -ERESTART_RESTARTBLOCK, then change eax (x86 ) to call
sys_restart which would in turn call the function in the
restart_block.

One of the problems with this is the way parameters are
passed to system calls.  One way to do this would be to have
sys_restart branch to the restart_function (requires asm). 
Another way is to just pass a struct pointer (actually the
reg struct) which the restart function could sort out.  For
example for nano_sleep:

int sys_restart(struct void parms)
{
	return (current->restart_block.sys_call) (&parms);

}
Then:
struct nano_sleep_call{
	struct timespec *tp;
	struct timespec *rem;
}
int restart_nano_sleep(struct nano_sleep_call *parm)
> 
> > My question is who sets up these values?  I think you are
> > saying it should be the system call.  Is this right?
> 
> Whatever system call that return -ERESTART_RESTARTBLOCK, yes.
> 
> So it would never get set up at all in the fast path. Only in the error
> case path of a system call that wants to have restarting capabilities.

And then only when returning -ERESTART_RESTARTBLOCK.
> 
>                 Linus
> 
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-- 
George Anzinger   george@mvista.com
High-res-timers: 
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Preemption patch:
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