Re: 2.4.6 possible problem

[Alex Ivchenko <aivchenko@ueidaq.com>]

Dick,

"Richard B. Johnson" wrote:
> 
> On Tue, 17 Jul 2001, Linus Torvalds wrote:
> 
> > In article <Pine.LNX.3.95.1010717103652.1430A-100000@chaos.analogic.com>,
> > Richard B. Johnson <root@chaos.analogic.com> wrote:
> > >
> > >    ticks = 1 * HZ;        /* For 1 second */
> > >    while((ticks = interruptible_sleep_on_timeout(&wqhead, ticks)) > 0)
> > >                  ;
> >
> > Don't do this.
> >
> > Imagine what happens if a signal comes in and wakes you up? The signal
> > will continue to be pending, which will make your "sleep loop" be a busy
> > loop as you can never go to sleep interruptibly with a pending signal.

Sleep like this is useless in real code. You either want your ioctl to unblock
when event (or time-out) happens or use sleep function to make driver wait certain 
amount of time (if you need to access poorly-designed hardware).

Off-topic:

>     I was going to compile a list of innovations that could be
>     attributed to Microsoft. Once I realized that Ctrl-Alt-Del
>     was handled in the BIOS, I found that there aren't any.
Well, give 'em at least some credit for copycating :-)
As a system architect I would say a *good* copycating.

For example:

Win32 events (CreateEvent(), WaitForxxxObject()) are very useful things.
The whole reason I was asking my questions is because I want to emulate Win32-like
event mechanism it Linux driver. I wouldn't mind to have this mechanism built into
Linux kernel. 

Say, one of the user process threads calls:
ret = WaitForSingleObject(hObject, dwTimeoutms);
or
ret = WaitForMultipleObjects(nNumber, hObjects[], FALSE, dwTimeoutms);

and waits until time-out or one (or more) objects are set.

>From the driver side you call:
KeSetEvent(hNotifyEvent, (KPRIORITY)1, FALSE);
when you want to release object.

It's very useful.
For example, with our hardware I can have up to 16*4 = 64 totally separated 
subsystems. Each subsystem can fire event asynchronously. It's much easier to
control each subsystem in separate thread and Win32 events are very handy.

-- 
Regards,
Alex

--
Alex Ivchenko, Ph.D.
United Electronic Industries, Inc.
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