linux-kernel - Re: [Patch 00/12] Hardware Breakpoint Interfaces

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Date:	Tue, 12 May 2009 16:39:16 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"K.Prasad" <prasad@...ux.vnet.ibm.com>
cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Benjamin Herrenschmidt <benh@....ibm.com>,
	<maneesh@...ux.vnet.ibm.com>, Roland McGrath <roland@...hat.com>
Subject: Re: [Patch 00/12] Hardware Breakpoint Interfaces

On Tue, 12 May 2009, K.Prasad wrote:

> hmmh...The (un)register_user_<> and __(un)register_user_<> break-up
> looks so modular and am not sure if combining them would be of any
> benefit (and as you might be aware, the compiler can always choose
> to inline though). And doing this might not be helpful if we like to
> virtualise the debug registers (as in the original implementation) in
> the future.

You can keep them separate if you like, but then at least make the "__" 
routines static and remove them from the .h file.

> The __modify_user_hw_breakpoint() had the "__" prefix because it had
> "int pos" as a parameter, although it can be eliminated by adding a loop
> that iterates through the breakpoints of "tsk". If you prefer
> modify_user_hw_breakpoint(), I will introduce the same in
> kernel/hw_breakpoint.c which acts as a wrapper over __modify_user_<> and
> takes the hw_breakpoint_lock.
> 
> Let me know what you think on the above.

Go ahead and introduce modify_user_hw_breakpoint().  Then the spinlock
can become static.


> Ok. Will change the code as suggested. The return values in the above
> implementation will be modified in the second pass here:
> 
> rc = __modify_user_hw_breakpoint(i, tsk, bp);
> 
> I will save the 'rc' value from the first pass in a separate variable
> and use that as the return value. Operations in the second pass (such as
> unregister/modify are not expected to fail).

That's right.

Alan Stern

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