From: Ian Kent <raven@themaw.net>
Subject: Re: [PATCH 1/2] NFS: Add the mount option "nosharecache"
Date: Fri, 18 May 2007 22:57:26 +0800
Message-ID: <1179500246.3726.7.camel@raven.themaw.net>
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	<20070517021318.32447.94991.stgit@heimdal.trondhjem.org>
	<1179457946.3726.3.camel@raven.themaw.net>
	<1179494402.6488.13.camel@heimdal.trondhjem.org>
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Cc: Neil Brown <neilb@suse.de>, Paul Krizak <paul.krizak@amd.com>,
	nfs@lists.sourceforge.net
To: Trond Myklebust <Trond.Myklebust@netapp.com>
In-Reply-To: <1179494402.6488.13.camel@heimdal.trondhjem.org>
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On Fri, 2007-05-18 at 09:20 -0400, Trond Myklebust wrote:
> On Fri, 2007-05-18 at 11:12 +0800, Ian Kent wrote:
> > How will the "read-only bind mounts" VFS changes affect this?
> 
> They won't. Dave's patches move the MS_RDONLY flag out of the
> super_block and into the vfsmount. That makes it possible to share the
> same super_block (and hence the same inode/dentry caches) between a
> read-only mount and a read-write mount.
> 
> If you want to change any of the other flags, though, you will still
> have to use nosharecache to do so: for instance if you want to set up a
> 'noac' mount for one directory, but want all other directories to cache
> attributes, then you will have to mount the "noac" directory using the
> nosharecache flag.
> 
> > When the fscache patches are merged how will this it be affect by this?
> 
> I'd suggest simply returning an error if the user tries to set both
> fscache and nosharecache. David's reasoning is still valid: if two
> superblocks try to write to the same fscache inode, then caching havoc
> will ensue.

Yep. David suggested that also.

> 
> Note, however, that the fscache patches already have a problem. I found
> out recently that RHEL-5 uses NFS_MOUNT_FSCACHE==0x4000, which is taken
> by NFS_MOUNT_NORDIRPLUS in mainline.

Yep, we'll need to work on fixing that. I'll talk with David.

Ian


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