linux-kernel - Re: [PATCH 6/6] fs: Introduce kern_mount

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Message-ID: <492E70B6.70108@cosmosbay.com>
Date:	Thu, 27 Nov 2008 11:04:38 +0100
From:	Eric Dumazet <dada1@...mosbay.com>
To:	Christoph Hellwig <hch@...radead.org>
CC:	Ingo Molnar <mingo@...e.hu>, David Miller <davem@...emloft.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	kernel-testers@...r.kernel.org, Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linux Netdev List <netdev@...r.kernel.org>,
	Christoph Lameter <cl@...ux-foundation.org>
Subject: Re: [PATCH 6/6] fs: Introduce kern_mount_special() to mount	special
 vfs

Christoph Hellwig a écrit :
> On Thu, Nov 27, 2008 at 12:32:59AM +0100, Eric Dumazet wrote:
>> This function arms a flag (MNT_SPECIAL) on the vfs, to avoid
>> refcounting on permanent system vfs.
>> Use this function for sockets, pipes, anonymous fds.
> 
> special is not a useful name for a flag, by definition everything that
> needs a flag is special compared to the version that doesn't need a
> flag.
> 
> The general idea of skippign the writer counts makes sense, but please
> give it a descriptive name that explains the not unmountable thing.
> And please kill your kern_mount wrapper and just set the flag manually.
> 
> Also I think it should be a superblock flag, not a mount flag as you
> don't want thse to differ for multiple mounts of the same filesystem.
> 
> 

Hum.. we have a superblock flag already, but testing it in mntput()/mntget()
is going to be a litle bit expensive if we add a derefence ?

if (mnt && mnt->mnt_sb->s_flags & MS_SPECIAL) {
   ...
}

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