Re: [PATCH (2.4)] atomic use count for proc_dir_entry

From: Ingo Oeser (ingo.oeser@informatik.tu-chemnitz.de)
Date: Fri Nov 17 2000 - 06:24:33 EST

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In reply to: Jacob Luna Lundberg: "Re: [PATCH (2.4)] atomic use count for proc_dir_entry"
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On Fri, Nov 17, 2000 at 12:35:03AM -0800, Jacob Luna Lundberg wrote:
> > atomic_dec_and_test() returns true.
>
> Indeed, after studying the asm in question I think I see how it ticks.
> What is the reasoning behind reversing the result of the test instead of
> returning the new value of the counter?

The full name of this operation is: "Decrement the value given
and test the result for equality with zero in one atomic operation".

So basically:

#define dec_and_test(i) ( (--i) ? 0 : 1)

but atomically.

This is implemented in hardware for some archs and a required
operation for proper and fast refcounting.

Regards

Ingo Oeser

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