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

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Message-ID: <50337D87.90607@parallels.com>
Date:	Tue, 21 Aug 2012 16:22:31 +0400
From:	Pavel Emelyanov <xemul@...allels.com>
To:	"J. Bruce Fields" <bfields@...ldses.org>
CC:	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Cyrill Gorcunov <gorcunov@...nvz.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	James Bottomley <jbottomley@...allels.com>,
	Matthew Helsley <matt.helsley@...il.com>
Subject: Re: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper

On 08/21/2012 04:11 PM, J. Bruce Fields wrote:
> On Tue, Aug 21, 2012 at 03:09:05PM +0400, Pavel Emelyanov wrote:
>> On 08/21/2012 02:54 PM, Cyrill Gorcunov wrote:
>>> On Tue, Aug 21, 2012 at 02:49:47PM +0400, Pavel Emelyanov wrote:
>>>>>>
>>>>>> However, if you have some better ideas on what information about inode should be exported
>>>>>> to the userspace please share.
>>>>>>
>>>>>
>>>>> Why not use name_to_handle(fd,...) and open_by_handle(handle,..) ?
>>>>
>>>> Because we don't have an fd at hands by the time we need to know the handle.
>>>
>>> Yeah, this might be not clear from patchset itself but inotify marks carry
>>> inodes inside kernel thus it's inodes what we can use when we fetch information
>>> about targets and put it into fdinfo output.
>>
>> Al, Bruce, Aneesh,
>>
>> What if we calculate the handle at the time we do have struct path at hands (i.e.
>> when we create the inotify) and store it on the inotify structure purely to be 
>> shown later in proc. Would that be acceptable?
> 
> Was it the lack of a dentry that was really the problem?  I thought it
> was just the fact that not all filesystems support filehandles.

Initial problem -- we don't know what is being watched by an inotify fd.

Having a dentry somewhere was the 1st attempt to solve this -- keep a path
in inotify and show it when required. It doesn't work since holding a ref on
path changes the behavior of watched inode (we cannot rename/unlink/remount
it the same way as we could before patching the kernel).

> --b.
> .
> 

Thanks,
Pavel
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