I''ve just started looking at Xen and I have some questions. These are
all fairly basic, as there is preciously little overview documentation
(most of it seems to be fairly detailed).
First of all, I''m coming from an UML (User-Mode Linux) and VMware
background. I''m using UML for a number of things, and I''m
generally
happy with it, except for the performance and lack of suspend/resume
functionality.
My questions:
-- as I understand, Xen *requires* running a custom kernel, it isn''t
just a user-level application like UML or VMware?
-- if yes, is it reasonable to expect that a patched (customized for a
laptop) kernel that includes swsusp2 and encryption (among other
things) will be able to support Xen?
-- is Xen at all suitable for the following usage scenario: a laptop
host, with frequently changing networking, software suspend (via
swsusp2), Xenolinux without real-world networking
(e.g. host<->Xenolinux communication only)?
I''d appreciate any advice.
thanks,
--J.
>I''ve just started looking at Xen and I have some questions. These are >all fairly basic, as there is preciously little overview documentation >(most of it seems to be fairly detailed). > >First of all, I''m coming from an UML (User-Mode Linux) and VMware >background. I''m using UML for a number of things, and I''m generally >happy with it, except for the performance and lack of suspend/resume >functionality. > >My questions: > > -- as I understand, Xen *requires* running a custom kernel, it isn''t > just a user-level application like UML or VMware?So Xen = "the host" from your point of view; however it is /not/ an operating system itself (i.e. it has no notion of filesystem, network stack, process, user, etc), and so you cannot do anything with a system without at least one guest OS. This is by contrast with UML and (most versions of) VMWare. The basic setup then is Xen + Domain 0. This is the first guest OS booted, and is booted via grub along with Xen itself. Domain 0 by default runs a XenoLinux kernel which is a modified kernel built to understand that it is running on top of Xen rather than the bare hardware. The XenoLinux kernel in turn allows proceses, etc, as per regular linux. In terms of priviliege levels: - Xen runs in ring 0 and can access all physical memory and devices - XenoLinux kernel runs in ring 1 and can access a subset of physical memory as allocated by Xen, and can access devices via Xen (this final bit is changing currently but is not yet ready for general release) - XenoLinux processes run in ring 3 exactly as per normal. Hence once you log into domain 0, it looks pretty much exactly like a regular linux, with full application binary compatability, etc. In addition there''s an extended interface which allows one to create additional guest operating systems (domains 1, 2, 3, ....), each with their own allocation of physical memory, virtual devices, etc.> -- if yes, is it reasonable to expect that a patched (customized for a > laptop) kernel that includes swsusp2 and encryption (among other > things) will be able to support Xen?So encryption should not be a problem; swsusp2 might be depending on how much power-management support it requires. To try this out you''d need to build a xenolinux kernel from scratch (i.e. get the source, build xen, build a xenolinux tree (see HOWTO), patch xenolinux tree, cross fingers, build, boot...). Note that the xenolinux kernel is based on 2.4.25 -- there is no support for 2.6 as yet.> -- is Xen at all suitable for the following usage scenario: a laptop > host, with frequently changing networking, software suspend (via > swsusp2), Xenolinux without real-world networking > (e.g. host<->Xenolinux communication only)?Laptop is fine in general (several of us run xen and xenolinux on our laptops), although some funky laptops may cause problems (we support only a subset of device drivers in the current model) Frequently changing networking: shouldn''t be a problem as long as standard linux stuff is used. So w.r.t suspend, see above. "Xenolinux without real-world networking (e.g. host<->Xenolinux communication only)" -- this doesn''t make much sense in our world as the ''host'' (Xen) is not itself doing any networking save for basic device driver stuff. The analagous setup for us would be domain 0 with ''real world'' networking, and all other domains with e.g. 169.254.x.y networking. This is a fairly standard setup for us (with NAT in domain 0 if you want ot allow other domains to access the real world, or no NAT if you don''t want this). Details in the HOWTOs and docs I belive.>I''d appreciate any advice.HTH, cheers, S.
> I''ve just started looking at Xen and I have some questions. These are > all fairly basic, as there is preciously little overview documentation > (most of it seems to be fairly detailed). > > First of all, I''m coming from an UML (User-Mode Linux) and VMware > background. I''m using UML for a number of things, and I''m generally > happy with it, except for the performance and lack of suspend/resume > functionality. > > My questions: > > -- as I understand, Xen *requires* running a custom kernel, it isn''t > just a user-level application like UML or VMware?Yes. It''s more like VMware ESX server: rather than having a ''hostOS'' there''s a custom VMM.> -- if yes, is it reasonable to expect that a patched (customized for a > laptop) kernel that includes swsusp2 and encryption (among other > things) will be able to support Xen?Given that the host is a custom VMM rather than linux, this question doesn''t make sense. You can suspend/migrate guest OSes, but not the host VMM itself. As regards encryption, you can compile it into the guests. There''s also some support for network encryption in the Xen 1.3vnet tree. This will be rather more complete in the new IO model in 1.4.> -- is Xen at all suitable for the following usage scenario: a laptop > host, with frequently changing networking, software suspend (via > swsusp2), Xenolinux without real-world networking > (e.g. host<->Xenolinux communication only)?Xen is (currently) more targeted at clusters of servers rather than laptops. However, I do have Xen installed on my Toshiba R100. Ian ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel
>>>>> "Steven" == Steven Hand <Steven.Hand@cl.cam.ac.uk>:>> I''ve just started looking at Xen and I have some questions. These >> are all fairly basic, as there is preciously little overview >> documentation (most of it seems to be fairly detailed). >> >> First of all, I''m coming from an UML (User-Mode Linux) and VMware >> background. I''m using UML for a number of things, and I''m generally >> happy with it, except for the performance and lack of suspend/resume >> functionality. [...many interesting explanations snipped...] >> -- if yes, is it reasonable to expect that a patched (customized for >> a laptop) kernel that includes swsusp2 and encryption (among >> other things) will be able to support Xen? Steven> So encryption should not be a problem; swsusp2 might be Steven> depending on how much power-management support it requires. To Steven> try this out you''d need to build a xenolinux kernel from Steven> scratch (i.e. get the source, build xen, build a xenolinux tree Steven> (see HOWTO), patch xenolinux tree, cross fingers, build, Steven> boot...). Steven> Note that the xenolinux kernel is based on 2.4.25 -- there is Steven> no support for 2.6 as yet. >> -- is Xen at all suitable for the following usage scenario: a laptop >> host, with frequently changing networking, software suspend (via >> swsusp2), Xenolinux without real-world networking >> (e.g. host<->Xenolinux communication only)? Steven> Laptop is fine in general (several of us run xen and xenolinux Steven> on our laptops), although some funky laptops may cause problems Steven> (we support only a subset of device drivers in the current Steven> model) [...] Thanks a lot for your (and Ian Pratt''s) answers. They have indeed helped me a lot in understanding whan Xen is (and what it is not). I was really looking for a way to make my virtual world persistent (suspendable and preferably also snapshottable) and independent of the crash of the day being served to me by Linux. In particular, the USB subsystem in Linux ranks highly among the crappiest things I have to use. From your explanations it seems that Xen is designed for virtual hosting environment and isn''t really the way to go for me. UML (user-mode linux) suits my needs better. Except it doesn''t have suspend/resume functionality. Oh well, I guess I''ll just have to wait for that. many thanks for your time, --J.
> Thanks a lot for your (and Ian Pratt''s) answers. They have indeed helped > me a lot in understanding whan Xen is (and what it is not). > > I was really looking for a way to make my virtual world persistent > (suspendable and preferably also snapshottable) and independent of the > crash of the day being served to me by Linux. In particular, the USB > subsystem in Linux ranks highly among the crappiest things I have to > use. > > From your explanations it seems that Xen is designed for virtual hosting > environment and isn''t really the way to go for me. UML (user-mode linux) > suits my needs better. Except it doesn''t have suspend/resume > functionality. Oh well, I guess I''ll just have to wait for that.We''re moving towards the type of features that you''re looking for, but we''re certainly not all the way there yet. For example, we are moving device drivers into their own domains -- this will allow you to run the Linux USB subsystem in an isolated domain and restart just that driver when it crashes (the rest of your machine, and your main OS, could continue to run with just a short dropout in communications with USB-connected devices). So, check back in a month or two and see what the answer is then. :-) -- Keir ------------------------------------------------------- This SF.Net email is sponsored by: IBM Linux Tutorials Free Linux tutorial presented by Daniel Robbins, President and CEO of GenToo technologies. Learn everything from fundamentals to system administration.http://ads.osdn.com/?ad_id=1470&alloc_id=3638&op=click _______________________________________________ Xen-devel mailing list Xen-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/xen-devel