linux-kernel - Re: [PATCH 1/2] rcu: introduce list_last_or_null

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Message-ID: <20150528211010.GA31229@cloud>
Date:	Thu, 28 May 2015 14:10:10 -0700
From:	josh@...htriplett.org
To:	Dan Streetman <ddstreet@...e.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] rcu: introduce list_last_or_null_rcu

On Thu, May 28, 2015 at 04:44:59PM -0400, Dan Streetman wrote:
> On Thu, May 28, 2015 at 4:42 PM, Dan Streetman <ddstreet@...e.org> wrote:
> > On Thu, May 28, 2015 at 4:39 PM,  <josh@...htriplett.org> wrote:
> >> On Thu, May 28, 2015 at 04:35:27PM -0400, Dan Streetman wrote:
> >>> Add list_last_or_null_rcu(), to simplify getting the last entry from a
> >>> rcu-protected list.  The standard list_last_entry() can't be used as it
> >>> is not rcu-protected; the list may be modified concurrently.  And the
> >>> ->prev pointer can't be used, as only the ->next pointers are protected
> >>> by rcu.
> >>>
> >>> This simply iterates forward through the entire list, to get to the last
> >>> entry.  If the list is empty, it returns NULL.
> >>>
> >>> Signed-off-by: Dan Streetman <ddstreet@...e.org>
> >>
> >> The list iteration functions are macros because they introduce a loop
> >> with attached loop block.  For this, is there any reason not to make it
> >> an inline function instead of a macro?
> >
> > true, there's no reason i can see not to make it inline, let me send
> > an updated patch.
> 
> ha, as soon as i sent that email, i realized it can't be an inline
> function, because the return value is (type *), not a predefined
> value.  Of course it could return void*, but unless there's a benefit
> of making it an inline function, it seems to me like it would be
> better as a #define.

Fair enough.  Sigh, C.

- Josh Triplett
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