Hi All, I have a query. How is a TCP connection state maintained across domUs and a remote client? Any pointers to the code will be really helpful. Second question ,Can I run a Xen hypervisor inside a domU, making this domU as the host and subsequent domUs as guests running over this guest domU ? Just asking this out of curiosity. Thank you ~psr -- --- pradeep singh rautela "Genius is 1% inspiration, and 99% perspiration" - not me :) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> -----Original Message----- > From: xen-devel-bounces@lists.xensource.com > [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of > pradeep singh rautela > Sent: 24 April 2007 13:43 > To: xen-devel > Subject: [Xen-devel] TCP state between domU and client > > Hi All, > > I have a query. > How is a TCP connection state maintained across domUs and a > remote client? > Any pointers to the code will be really helpful.This is ABSOLUTELY the same as if you have a connection between a "bare-metal" machine, it''s handled in the TCP-layer which is unchanged between Xen and native Linux. If you don''t understand how that works, then you probably need to look at documentation of how the Linux TCP-stack works. For the TCP-layer, there''s no need to understand if a machine is a real physical machine or a virtual machine.> > Second question ,Can I run a Xen hypervisor inside a domU, > making this domU as the host and subsequent domUs as guests > running over this guest domU ? Just asking this out of curiosity.Yes, no, maybe. You can (so I''ve been told, I haven''t tried) run Xenified Linux on top of a HVM DomU. Obviously, any guest on top of that would not be able to use the HVM feature, as that is a "single-layer". But for para-virtual domains, you can''t run the hypervisor on top of itself, because the hypervisor needs Ring0 (the most privileged protection level). Any subsequent load would fail to control this level, so it''s not possible to run the hypervisor at this level. It is also pretty pointless (aside from the fun and games you can have with it, and I guess it''s proving a point, in the same way as compiling the source for the compiler with itself proves that the compiler is working pretty well [This can also be more useful, as the compiler is perhaps able to do optimization that isn''t available in the previous compiler]). -- Mats> > Thank you > > ~psr > > > -- > --- > pradeep singh rautela > > "Genius is 1% inspiration, and 99% perspiration" - not me :) >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
pradeep singh rautela
2007-Apr-24 13:30 UTC
Re: [Xen-devel] TCP state between domU and client
On 4/24/07, Petersson, Mats <Mats.Petersson@amd.com> wrote:> > > > > -----Original Message----- > > From: xen-devel-bounces@lists.xensource.com > > [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of > > pradeep singh rautela > > Sent: 24 April 2007 13:43 > > To: xen-devel > > Subject: [Xen-devel] TCP state between domU and client > > > > Hi All, > > > > I have a query. > > How is a TCP connection state maintained across domUs and a > > remote client? > > Any pointers to the code will be really helpful. > > This is ABSOLUTELY the same as if you have a connection between a > "bare-metal" machine, it''s handled in the TCP-layer which is unchanged > between Xen and native Linux. If you don''t understand how that works, > then you probably need to look at documentation of how the Linux > TCP-stack works. For the TCP-layer, there''s no need to understand if a > machine is a real physical machine or a virtual machine.got it.> > > Second question ,Can I run a Xen hypervisor inside a domU, > > making this domU as the host and subsequent domUs as guests > > running over this guest domU ? Just asking this out of curiosity. > > Yes, no, maybe. You can (so I''ve been told, I haven''t tried) run > Xenified Linux on top of a HVM DomU. Obviously, any guest on top of that > would not be able to use the HVM feature, as that is a "single-layer". > > But for para-virtual domains, you can''t run the hypervisor on top of > itself, because the hypervisor needs Ring0 (the most privileged > protection level). Any subsequent load would fail to control this level, > so it''s not possible to run the hypervisor at this level.Thank a lot Mats ~psr It is also pretty pointless (aside from the fun and games you can have> with it, and I guess it''s proving a point, in the same way as compiling > the source for the compiler with itself proves that the compiler is > working pretty well [This can also be more useful, as the compiler is > perhaps able to do optimization that isn''t available in the previous > compiler]). > > -- > Mats > > > > Thank you > > > > ~psr > > > > > > -- > > --- > > pradeep singh rautela > > > > "Genius is 1% inspiration, and 99% perspiration" - not me :) > > > > >-- --- pradeep singh rautela "Genius is 1% inspiration, and 99% perspiration" - not me :) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> > Second question ,Can I run a Xen hypervisor inside a domU, > > making this domU as the host and subsequent domUs as guests > > running over this guest domU ? Just asking this out of curiosity. > > Yes, no, maybe. You can (so I''ve been told, I haven''t tried) run > Xenified Linux on top of a HVM DomU. Obviously, any guest on top of that > would not be able to use the HVM feature, as that is a "single-layer".I do most of my testing of development versions of Xen within an HVM domain running on xen-unstable. My reasons for this are as follows: 1) I only need paravirtual domains for my work, and Xen running in an HVM domain supports them just fine. 2) My real physical machine doesn''t have a serial console or a remote power switch. Using xm console and xm reboot, my HVM domain does. 3) I can have several different HVM domains testing different Xen versions configured at once. 4) The host machine can be maintained at a known-good version of Xen. Tricks with suspend / resume could be used to make working with these even more efficient; I''ve not tried that yet.> But for para-virtual domains, you can''t run the hypervisor on top of > itself, because the hypervisor needs Ring0 (the most privileged > protection level). Any subsequent load would fail to control this level, > so it''s not possible to run the hypervisor at this level.Yep. Without HVM support, you''re limited to using something like Qemu / VMware... I''m working on being able to rsync my Xen development domain over to my laptop (no HVM) and run it under Qemu when away from my dedicated test box. The only limitations I''ve found with my setup are: 1) It''s slower than native. 2) Compiling PV-on-HVM drivers for the guest''s dom0 gets a bit confused and doesn''t work (I just use ioemu devices instead). 3) Xenoprof doesn''t work for a Xen running within an HVM domain - I''m guessing NMIs aren''t being delivered or something like that, but it''s not a big problem for most of my work. Cheers, Mark> It is also pretty pointless (aside from the fun and games you can have > with it, and I guess it''s proving a point, in the same way as compiling > the source for the compiler with itself proves that the compiler is > working pretty well [This can also be more useful, as the compiler is > perhaps able to do optimization that isn''t available in the previous > compiler]). > > -- > Mats > > > Thank you > > > > ~psr > > > > > > -- > > --- > > pradeep singh rautela > > > > "Genius is 1% inspiration, and 99% perspiration" - not me :) > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel-- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> I have a query. > How is a TCP connection state maintained across domUs and a remote client? > Any pointers to the code will be really helpful.In general, Xen is well out of the way of this as Mats explained. Xen provides virtual network devices and normal TCP mechanisms operate over the top of this. I believe Xen arranges for an ARP advertisement to be sent to the network (actually, the guest''s driver does this) when a live migration is completed. This is not strictly necessary, but it ensures that the other entities on the network know that the guest has moved so that the TCP connection doesn''t hang until the VM is rediscovered... I imagine this is primarily so that switched networks can change their knowledge of the topology; don''t know if there are any other issues involved. Cheers, Mark> Second question ,Can I run a Xen hypervisor inside a domU, making this domU > as the host and subsequent domUs as guests running over this guest domU ? > Just asking this out of curiosity. > > Thank you > > ~psr-- Dave: Just a question. What use is a unicyle with no seat? And no pedals! Mark: To answer a question with a question: What use is a skateboard? Dave: Skateboards have wheels. Mark: My wheel has a wheel! _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
pradeep singh rautela
2007-Apr-25 06:16 UTC
Re: [Xen-devel] TCP state between domU and client
On 4/24/07, Mark Williamson <mark.williamson@cl.cam.ac.uk> wrote:> > > I have a query. > > How is a TCP connection state maintained across domUs and a remote > client? > > Any pointers to the code will be really helpful. > > In general, Xen is well out of the way of this as Mats explained. Xen > provides virtual network devices and normal TCP mechanisms operate over > the > top of this. > > I believe Xen arranges for an ARP advertisement to be sent to the network > (actually, the guest''s driver does this) when a live migration is > completed. > This is not strictly necessary, but it ensures that the other entities on > the > network know that the guest has moved so that the TCP connection doesn''t > hang > until the VM is rediscovered...Thanks Mark, that was perfectly what i was looking for. Can i have a pointer to code? That will be really helpful. Thank a lot once again. ~psr I imagine this is primarily so that switched networks can change their> knowledge of the topology; don''t know if there are any other issues > involved. > > Cheers, > Mark > > > Second question ,Can I run a Xen hypervisor inside a domU, making this > domU > > as the host and subsequent domUs as guests running over this guest domU > ? > > Just asking this out of curiosity. > > > > Thank you > > > > ~psr > > > > -- > Dave: Just a question. What use is a unicyle with no seat? And no pedals! > Mark: To answer a question with a question: What use is a skateboard? > Dave: Skateboards have wheels. > Mark: My wheel has a wheel! >-- --- pradeep singh rautela "Genius is 1% inspiration, and 99% perspiration" - not me :) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel