Re: [PATCH v2 0/3] Add support for NetBSD gntdev

[Roger Pau Monné <roger.pau%citrix.com@localhost>]

On 30/11/12 10:41, Manuel Bouyer wrote:
> On Fri, Nov 30, 2012 at 10:21:02AM +0100, Roger Pau Monné wrote:
>>> And I don't like the idea of software doing things in my back.
>>> And, beside this, I don't think local vs remote is the right criteria.
>>> There are remote filesystems which may play nice with vnd. There
>>> are local filesystems that may not play nice with vnd.
>>
>> I would agree with you if this was a DomU crash, but in this case the
>> crash happens in the Dom0, and every DomU that the system might be
>> running crashes completely. This is not acceptable in any way from my
>> point of view.
>>
>> I think we should not expect the user to be aware of this kind of
>> problems. If we cannot guarantee that the vnd driver is functional for
>> all filesystems, we should not use it. From my point of view reliability
>> should always come before performance.
> 
> In my POV, the admin show know what he's doing. This includes be aware of the
> limitations of the software he uses. A 50% performances loss just "in case"
> is not accetpable. Or at last last there should be a way for the admin
> to revert to an acceptable configuration, performance wise, without
> hacking and rebuilding from sources.

There are also other tools that build on top of libxl, like libvirt, are
we going to modify those high level tools to add a new option to the
config file if the disk of a DomU is in NFS and the Dom0 is NetBSD? I
don't think we should take that road, I think libxl should take care of
all those quicks, and provide an uniform layer that can be trusted
independently of the environment, so the same configuration file can be
used in all supported Dom0 OSes.

Not fixing this in libxl just moves the problem a layer upper, where
there's a lot more of options, and of course a lot more of work to track
and fix them all.