linux-kernel - Re: [PATCH 1/4] dynamic_debug: consolidate repetitive struct

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Date:	Mon, 12 Sep 2011 10:47:18 -0400
From:	Jason Baron <jbaron@...hat.com>
To:	Joe Perches <joe@...ches.com>
Cc:	Jim Cromie <jim.cromie@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>, gregkh@...e.de,
	Bart Van Assche <bvanassche@....org>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] dynamic_debug: consolidate repetitive struct _ddebug
 descriptor definitions

On Fri, Sep 09, 2011 at 03:32:05PM -0700, Joe Perches wrote:
> > The trick is then to allow those users to define flag-chars that they like
> > (mnemonic value), and that work with the dynamic-debug mini-language
> > implemented in $CONTROL reader.
> 
> I don't think that's a problem really.
> 
> I think a simple control/test variable as either value
> or mask would work fine.
> 
> Take a single bit control to either test as mask
> or test as level.  No mnemonic letters needed.
> 
> pr_debug_mask(mask, fmt, ...)
> pr_debug_level(level, fmt, ...)
> 
> could set the appropriate type bit in the struct
> so the test works as appropriate.
> 
> echo 'value <foo>' > <debugfs>/dynamic_debug/control
> 
> > But that begs the question - is there a reason why __aligned(4)
> > wouldnt work for 32 bit machines ?   It would reduce the footprint
> > for small machines.
> 
> No real idea why it's aligned(8).  Jason?
> 

I think when I first implemented it, I noticed that subsystems that did
similar things, set aligned(8) in include/asm-generic/vmlinux.lds.h. For
example, FTRACE_EVENTS() sets ALIGN(8)...I know that not a great reason
thouh :( Don't remember if I tried ALIGN(4), but if it saves space, we
can look at it...

Also, as I mentioned before, we probably need an extra array of pointers into
the dynamic debug structures. see: https://lkml.org/lkml/2011/1/26/463.

thanks,

-Jason
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