linux-ext4 - Re: [PATCH 03/10 v3] ext4: add physical block and status member into extent status tree

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Message-ID: <20130203052113.GA9823@gmail.com>
Date:	Sun, 3 Feb 2013 13:21:13 +0800
From:	Zheng Liu <gnehzuil.liu@...il.com>
To:	Theodore Ts'o <tytso@....edu>
Cc:	linux-ext4@...r.kernel.org, Zheng Liu <wenqing.lz@...bao.com>,
	Christopher Li <sparse@...isli.org>,
	linux-sparse@...r.kernel.org
Subject: Re: [PATCH 03/10 v3] ext4: add physical block and status member into
 extent status tree

On Sat, Feb 02, 2013 at 10:03:43PM -0500, Theodore Ts'o wrote:
> On Wed, Jan 30, 2013 at 10:43:33AM +0800, Zheng Liu wrote:
> > 
> > Clang is first coming in my mind.  I know that some one try to use it
> > to build a linux kernel and get a lot of problems that are about gcc
> > extension.  But for us it seems that things are not too bad. ;)
> 
> Clang accepts bitfields with "unsigned long long", but I've discovered
> something which does _not_ support unsigned long long --- the "sparse"
> tool.  :-(

Yes, this problem has been reported by Fengguang.  So I am plan to use
another method to define extent_status structure as last time we
discuessed.  What do you think?

Thanks,
                                                - Zheng

> 
> I discovered this when running "make C=1", i.e.:
> 
>   rm -f fs/ext4/extents_status.o
>   make C=1 fs/ext4/extents_status.o
> 
> Here's a simple test case which demo's that sparse doesn't deal well
> with unsigned long long.  If we change the last two fields in struct
> extents_status to:
> 
> 	unsigned long es_pblk : 30;	/* first physical block */
> 	unsigned long es_status : 2;	/* record the status of extent */
> 
> sparse doesn't complain.  But as shown below, sparse complains bitterly:
> 
> /tmp/foo.c:22:24: warning: invalid access past the end of 'es' (24 28)
> 
> I'm not sure Chris will consider this a bug, since bitfields
> with "unsigned long long" isn't standards complaint, even if gcc and
> clang supports it.   Chris, what do you think?
> 
>               	       		      	       - Ted
>    	
> 
> #!/bin/sh
> cat > /tmp/foo.c << EOF
> #include <unistd.h>
> #include <stdio.h>
> 
> struct rb_node {
> 	unsigned long  __rb_parent_color;
> 	struct rb_node *rb_right;
> 	struct rb_node *rb_left;
> } __attribute__((aligned(sizeof(long))));
> 
> struct extent_status {
> 	struct rb_node rb_node;
> 	unsigned long es_lblk;		/* first logical block extent covers */
> 	unsigned long es_len;		/* length of extent in block */
> 	unsigned long long es_pblk : 62;	/* first physical block */
> 	unsigned long long es_status : 2;	/* record the status of extent */
> };
> 
> int main(int argc, char **argv)
> {
> 	struct extent_status es;
> 
> 	es.es_status = 3;
> 
> 	printf("%d\n", es.es_status);
> 	printf("size %u\n", sizeof(es));
> }
> EOF
> sparse /tmp/foo.c
> --
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