linux-kernel - Re: [PATCH] Add list_for_each

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Message-ID: <20080216161958.GC27468@linux.vnet.ibm.com>
Date:	Sat, 16 Feb 2008 08:19:58 -0800
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Adrian Bunk <bunk@...nel.org>
Cc:	linux-kernel@...r.kernel.org, davem@...emloft.net,
	dipankar@...ibm.com
Subject: Re: [PATCH] Add list_for_each_rcu to features-removal list

On Sat, Feb 16, 2008 at 10:47:23AM +0200, Adrian Bunk wrote:
> On Mon, Jan 28, 2008 at 04:25:00AM -0800, Paul E. McKenney wrote:
> > Hello!
> > 
> > The list_for_each_entry_rcu() primitive should be used instead of
> > list_for_each_rcu(), as the former is easier to use and provides
> > better type safety.  This patch therefore adds list_for_each_rcu()
> > to the Documentation/feature-removal-schedule.txt file (for mid-2008)
> > and marks its comment header deprecated.
> > 
> > Signed-off-by: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > ---
> > 
> >  Documentation/feature-removal-schedule.txt |   10 ++++++++++
> >  include/linux/list.h                       |    5 ++++-
> >  2 files changed, 14 insertions(+), 1 deletion(-)
> > 
> > diff -urpNa -X dontdiff linux-2.6.24/Documentation/feature-removal-schedule.txt linux-2.6.24-dep-lfeRCU/Documentation/feature-removal-schedule.txt
> > --- linux-2.6.24/Documentation/feature-removal-schedule.txt	2008-01-24 14:58:37.000000000 -0800
> > +++ linux-2.6.24-dep-lfeRCU/Documentation/feature-removal-schedule.txt	2008-01-28 04:00:49.000000000 -0800
> > @@ -333,3 +333,13 @@ Why:	This driver has been marked obsolet
> >  Who:	Stephen Hemminger <shemminger@...ux-foundation.org>
> >  
> >  ---------------------------
> > +
> > +What:	list_for_each_rcu() primitive
> > +When:	July 2008
> > +Files:	include/linux/list.h
> > +Why:	The list_for_each_entry_rcu() primitive should be used instead,
> > +	as it is less error-prone and provides better type safety.
> > +Who:	Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> >...
> 
> Declaring something as deprecated doesn't automatically convert the 
> in-kernel users.

Understood.

> And once there are no in-kernel users left you can kill it immediately.

Hmmm...  What is the purpose of Documentation/feature-removal-schedule.txt
in that case?

> The only working way for getting rid of list_for_each_rcu() is:
> - send patches for all in-kernel usages to the maintainers of the code
>   in question now

That has happened at least once.

> - once all of these patches have entered Linus' tree (which might not
>   be before the 2.6.26 merge window) you can remove list_for_each_rcu()

So your approach would be to mark the macro obsolete to prevent additional
uses in the meantime?

							Thanx, Paul
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