linux-kernel - Re: [Xen-devel] [PATCH 1/2] xen: wrap xenbus on xenfs with COMPAT option

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Date:	Tue, 1 Dec 2015 13:54:19 +0000
From:	David Vrabel <david.vrabel@...rix.com>
To:	Doug Goldstein <cardoe@...doe.com>, <linux-kernel@...r.kernel.org>
CC:	<xen-devel@...ts.xenproject.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Subject: Re: [Xen-devel] [PATCH 1/2] xen: wrap xenbus on xenfs with COMPAT
 option

On 01/12/15 13:45, Doug Goldstein wrote:
> On 12/1/15 4:44 AM, David Vrabel wrote:
>> On 01/12/15 10:42, David Vrabel wrote:
>>> On 30/11/15 21:35, Doug Goldstein wrote:
>>>> Since Xen 4.6.0, using xenbus via xenfs (/proc/xen/xenbus) is deprecated
>>>> and /dev/xen/xenbus via pvops is used instead. This is an effort to
>>>> eventually drop this interface after a reasonable amount of time.
>>>
>>> I would prefer the ... /proc/xen/evtchn files to be
>>
>> I meant /proc/xen/privcmd here.
>>
>> David
>>
> 
> I can look into that. I do have a few questions, some of which are out
> of scope from the original patch.
> 
> Would it be preferable to just remove "xenbus" from the xenfs
> filesystem? Ever since Linux 3.14 even if you are running a version of
> Xen earlier than 4.6 you will not be able to have a disaggregated
> xenstore (which is the xenbus consumer) due to the addition of F_ATOMIC_POS.

If /proc/xen/xenbus is made a symlink then older Xen toolstacks will
work again.

> Is it safe for a kernel virtual filesystem to provide a symlink outside
> of itself where the destination can't be verified?

Yes.  The symlink target is just a string containing a path.

> Since the /proc/xen mount point has been marked as COMPAT for nearly 6
> years would the eventual goal be to move xenfs to somewhere like
> /sys/hypervisor given that most of the virtual filesystems are mounted
> under /sys now days?

No. The information might move to /sys/hypervisor (or elsewhere) but
xenfs will always be mounted in /proc/xen (or not mounted at all).

David
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