linux-kernel - Re: [PATCH 1/6] sysfs: Basic support for multiple super blocks

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Message-ID: <m1mxxoy4g0.fsf@fess.ebiederm.org>
Date:	Wed, 31 Mar 2010 07:02:39 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"Serge E. Hallyn" <serue@...ibm.com>
Cc:	Tejun Heo <tj@...nel.org>, Greg Kroah-Hartman <gregkh@...e.de>,
	Kay Sievers <kay.sievers@...y.org>,
	linux-kernel@...r.kernel.org,
	Cornelia Huck <cornelia.huck@...ibm.com>,
	linux-fsdevel@...r.kernel.org,
	Eric Dumazet <eric.dumazet@...il.com>,
	Benjamin LaHaise <bcrl@...et.ca>, netdev@...r.kernel.org
Subject: Re: [PATCH 1/6] sysfs: Basic support for multiple super blocks

"Serge E. Hallyn" <serue@...ibm.com> writes:

> Quoting Eric W. Biederman (ebiederm@...ssion.com):
>> Tejun Heo <tj@...nel.org> writes:
>> >> index 30f5a44..030a39d 100644
>> >> --- a/fs/sysfs/sysfs.h
>> >> +++ b/fs/sysfs/sysfs.h
>> >> @@ -114,6 +114,9 @@ struct sysfs_addrm_cxt {
>> >>  /*
>> >>   * mount.c
>> >>   */
>> >> +struct sysfs_super_info {
>> >> +};
>> >> +#define sysfs_info(SB) ((struct sysfs_super_info *)(SB->s_fs_info))
>> >
>> > Another nit picking.  It would be better to wrap SB in the macro
>> > definition.  Also, wouldn't an inline function be better?
>> 
>> Good spotting.  That doesn't bite today but it will certainly bite
>> someday if it isn't fixed.
>> 
>> I wonder how that has slipped through the review all of this time.
>
> (let me demonstrate how: )
>
> WTH are you talking about?  Unless you mean doing (SB) inside
> the definition?
>
> I actually was going to suggest dropping the #define as it obscures
> the code, but I figured it would get more complicated later.

I believe the discuss change was to make the define:
#define sysfs_info(SB) ((struct sysfs_super_info *)((SB)->s_fs_info))

As for dropping the define and using s_fs_info raw.  I rather like
a light weight type safe wrapper.  Maybe I just think s_fs_info
is an ugly name.

In practice I never call sysfs_info() with any expression that has
a side effect, so it doesn't matter.

Eric



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