linux-kernel - Re: [PATCH] Add list_for_each

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Date:	Sat, 16 Feb 2008 18:39:39 +0200
From:	Adrian Bunk <bunk@...nel.org>
To:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
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 08:19:58AM -0800, Paul E. McKenney wrote:
> 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?

I don't see any reason for not userspace visible things to be listed in
feature-removal-schedule.txt (with module names counted as being 
userspace visible) - they can be removed as soon as the last in-kernel 
user is gone.

> > 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.

Resend the patches (with a Cc to linux-kernel) until all of them got 
picked up...

> > - 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?

That can't harm.

But realistically, the only way to prevent additional uses is to 
completely remove it...

> 							Thanx, Paul

cu
Adrian

-- 

  An architecture specific patch that breaks the one architecture it 
  touches at the first file being compiled is even for kernel standards 
  unusually bad...
                                Me about a recent commit in Linus' tree

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