linux-kernel - Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV

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Date:	Thu, 16 Feb 2012 01:56:08 +0100
From:	Andrea Righi <andrea@...terlinux.com>
To:	Arun Sharma <asharma@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Minchan Kim <minchan.kim@...il.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Johannes Weiner <jweiner@...hat.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Rik van Riel <riel@...hat.com>,
	Hugh Dickins <hughd@...gle.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Shaohua Li <shaohua.li@...el.com>,
	Pádraig Brady <P@...igBrady.com>,
	John Stultz <john.stultz@...aro.org>,
	Jerry James <jamesjer@...terlinux.com>,
	Julius Plenz <julius@...nz.com>, linux-mm <linux-mm@...ck.org>,
	linux-fsdevel@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 3/3] fadvise: implement POSIX_FADV_NOREUSE

On Wed, Feb 15, 2012 at 03:57:47PM -0800, Arun Sharma wrote:
> 
> 
> On 2/15/12 3:47 PM, Andrea Righi wrote:
> >>index 74b6a97..b4e45e6 100644
> >>--- a/include/linux/fs.h
> >>+++ b/include/linux/fs.h
> >>@@ -9,7 +9,6 @@
> >>  #include<linux/limits.h>
> >>  #include<linux/ioctl.h>
> >>  #include<linux/blk_types.h>
> >>-#include<linux/kinterval.h>
> >>  #include<linux/types.h>
> >>
> >>  /*
> >>@@ -656,7 +655,7 @@ struct address_space {
> >>  	spinlock_t		private_lock;	/* for use by the address_space */
> >>  	struct list_head	private_list;	/* ditto */
> >>  	struct address_space	*assoc_mapping;	/* ditto */
> >>-	struct rb_root		nocache_tree;	/* noreuse cache range tree */
> >>+	void			*nocache_tree;	/* noreuse cache range tree */
> >>  	rwlock_t		nocache_lock;	/* protect the nocache_tree */
> >>  } __attribute__((aligned(sizeof(long))));
> >>  	/*
> >
> >mmh.. a forward declaration of rb_root in fs.h shouldn't be better than
> >this?
> >
> 
> Forward declaration works if the type was struct rb_root *. But the
> type in your patch was a struct and the compiler can't figure out
> its size.
> 
> include/linux/fs.h:659:17: error: field ‘nocache_tree’ has incomplete type
> 
> Did you mean forward declaring struct rb_node instead of rb_root?
> 
> If we go down this path, a few more places need fixups (I ignored
> the compiler warnings about casting void * to struct rb_root *).
> 
>  -Arun

Oh sorry, you're right! nocache_tree is not a pointer inside
address_space, so the compiler must know the size.

mmh... move the definition of the rb_root struct in linux/types.h? or
simply use a rb_root pointer. The (void *) looks a bit scary and too bug
prone.

-Andrea
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