linux-kernel - Re: [patch 4/8] fs, exportfs: Add export_encode_inode

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Date:	Fri, 17 Aug 2012 13:58:31 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Al Viro <viro@...IV.linux.org.uk>
Cc:	Cyrill Gorcunov <gorcunov@...nvz.org>,
	James Bottomley <jbottomley@...allels.com>,
	Pavel Emelianov <xemul@...allels.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel\@vger.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Matthew Helsley <matt.helsley@...il.com>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper

Al Viro <viro@...IV.linux.org.uk> writes:

> On Thu, Aug 16, 2012 at 06:15:53PM +0400, Cyrill Gorcunov wrote:
>> On Thu, Aug 16, 2012 at 02:03:00PM +0000, James Bottomley wrote:
>> > > > What's wrong with saying "we don't support idiotify"?
>> > > 
>> > > Al, we need some way to restore inotifies after checkpoint.
>> > > At the very early versions of these patches I simply added
>> > > dentry to the inotify mark thus once inotify created we always
>> > > have a dentry to refer on in encode_fh, but I'm not sure if
>> > > this will be good design.
>> > 
>> > Actually, I was about to suggest this.  This can be done internally
>> > within fs/notify without actually modifying the syscall interface, can't
>> > it, since they take a path which is used to obtain the inode?  It looks
>> > like the whole of the inotify interface could be internally recast to
>> > use dentries instead of inodes.  Unless I've missed something obvious?
>> 
>> Well, after looking into do_sys_name_to_handle->exportfs_encode_fh
>> sequence more precisely it seems it will be easier to extend
>> exportfs_encode_fh to support inodes directly instead of playing
>> with notify code (again, if i'm not missing something too).
>> i'm cooking a patch to show (once it's tested i'll send it out).
>
> Good luck doing that with e.g. VFAT...  And then there's such thing
> as filesystems that don't have ->encode_fh() for a lot of very good
> reasons; just try to do that on sysfs, for example.  Or on ramfs,
> for that matter...  And while saying "you can't export that over
> NFS" seems to work fine, idiotify-lovers will screech if you try
> to ban their perversion of choice on those filesystems.

For whatever it is worth inotify does not currently work on sysfs or
procfs or any other filesystem that looks like a network filesystem and
whose modifications don't proceed through the vfs like a normal
filesystem.

Eric
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