Re: [PATCH] libxl: stat the path for all non-qdisk backends (including unknown)

[George Dunlap <george.dunlap@eu.citrix.com>]

On 10/05/13 14:49, Ian Campbell wrote:
> On Fri, 2013-05-10 at 14:46 +0100, George Dunlap wrote:
>> On Fri, Apr 26, 2013 at 3:29 PM, Ian Campbell <Ian.Campbell@citrix.com> wrote:
>>> On Fri, 2013-04-26 at 15:17 +0100, Sylvain Munaut wrote:
>>>>> Since the intention of that commit was to allow for qdisk backends with no
>>>>> explicit file in dom0 (i.e. network remote backend such as ceph) the lowest
>>>>> impact fix appears to be to make that explicit. This should probably be
>>>>> revisited to rationalize the probing.
>>>> What about the remote disk case of blktap ?  blktap2.5 supports NBD
>>>> already AFAIK
>>>> and I'm pretty sure I'll hit that same stat issue soon for another
>>>> remote blktap case.
>>> Right, sounds like I should have gone with my first instinct which was:
>>>
>>> 8<------------------------------------------------------------
>>>
>>>  From 884beff4a897d785f61705dcfa2f048536982d7c Mon Sep 17 00:00:00 2001
>>> From: Ian Campbell <ian.campbell@citrix.com>
>>> Date: Fri, 26 Apr 2013 12:41:43 +0100
>>> Subject: [PATCH] libxl: stat the path for all non-qdisk backends (including unknown)
>>>
>>> The commit a8a1f236a296 "libxl: Only call stat() when adding a disk if we
>>> expect a device to exist." changed things to only stat the file when the phy
>>> backend was explicitly requested. This broke the case where we are probing and
>>> would normally be able to decide on the phy option.
>> So at the moment qdisk backends aren't checked at all with this --
>> which means that if you give a path to a file that doesn't exist via,
>> for example, xl cd-insert, things fail in weird ways:
>>
>> 1. In qemu-traditional, the command silently completes; the effect is
>> that the disk currently in the drive is ejected
>>
>> 2. in qemu-upstream, qmp returns an error which is reported.  The disk
>> is ejected from the guest, but the xenstore entries are not updated
>> (still contain the old values)
>>
>> It seems like we should probably also at least check if disk_format is RAW.
> A kit if these issues will come back with disk driver domains I think.
>
>> OTOH, I don't seen an option for disk_format to be ceph; is it just
>> listed as "raw" as well?  That doesn't seem right...
> That might well be the correct answer, but not for 4.3 I suspect?

I can't resolve this into an unambiguous meaning that makes sense. :-)  
Are you saying that ceph *should* be "raw" long-term, but that it 
shoudln't be for 4.3?  Or that right now ceph *is* raw, but we should 
change it for 4.3?  Or that we should change it long-term but leave it 
for 4.3?

  -George