Xen Documentation

[Gastón Keller]

Hello, everybody. I have been struggling with Xen's documentation
lately, not finding where to look for accurate and up-to-date info. I
remember having read in this list months ago someone saying that the
documentation was quite outdated. For example, the xm command _delete_
does not appear in the man pages and many guides still do reference to
the guest's config files being stored at /etc/xen (two days ago I
discovered that now Xen works in a different way).

My objective is not only to learn how to use Xen, but understand how
it works. I'm doing my best looking for info in the net and going
through docs in the Xen Wiki, but I might be missing something in my
search. Therefore, I would really appreciate if someone could point me
to some documentation I should read, or whatever else you could think
of.

Thanks,
Gaston

-- 
La única verdad es la realidad.

[Emre Erenoglu]

Hi Gaston,

It's true that some documentation is outdated. However, for the "/etc/xen"
isssue, my custom Xen 3.2 setup still stores ( and I do store there also) my
config files there.

Maybe what you're saying is "Fedora Specific" which I could understand as
it's fedora mailing list. However, I never found the flexibility and control
in the Fedora way of Xen implementation (all those xml stuff etc.).  most
probably, I'm wrong :)

Emre

On Thu, May 29, 2008 at 9:22 PM, Gastón Keller <gastonkeller(a)gmail.com&gt;
wrote:

>  Hello, everybody. I have been struggling with Xen's
> documentation
>  lately, not finding where to look for accurate and up-to-date info. I
>  remember having read in this list months ago someone saying that the
>  documentation was quite outdated. For example, the xm command _delete_
>  does not appear in the man pages and many guides still do reference to
>  the guest's config files being stored at /etc/xen (two days ago I
>  discovered that now Xen works in a different way).
>
>  My objective is not only to learn how to use Xen, but understand how
>  it works. I'm doing my best looking for info in the net and going
>  through docs in the Xen Wiki, but I might be missing something in my
>  search. Therefore, I would really appreciate if someone could point me
>  to some documentation I should read, or whatever else you could think
>  of.
>
>  Thanks,
>  Gaston
>
>  --
>  La única verdad es la realidad.
>
>  --
>  Fedora-xen mailing list
>  Fedora-xen(a)redhat.com
>  https://www.redhat.com/mailman/listinfo/fedora-xen
>  


-- 
Emre

[Gastón Keller]

On Thu, May 29, 2008 at 7:53 PM, Emre ERENOGLU <erenoglu(a)gmail.com&gt; wrote:
>  Hi Gaston,
>
>  It's true that some documentation is outdated. However, for the "/etc/xen"
>  isssue, my custom Xen 3.2 setup still stores ( and I do store there also) my
>  config files there.
>
>  Maybe what you're saying is "Fedora Specific" which I could understand as
>  it's fedora mailing list. 
_The Fedora team has followed the Xensource model and begun to store
all VM configuration details in a database, referred to as xenstore._
Source:
http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...

Then, you might be right. I interpreted it was a modification from
Xen, not from Fedora (previously introduced by Xensource).

So, what is the advantage behind this movement?

Thanks,
Gaston

 However, I never found the flexibility and control
>  in the Fedora way of Xen implementation (all those xml stuff etc.). 
> most
>  probably, I'm wrong :)
>
>  Emre
>
>  On Thu, May 29, 2008 at 9:22 PM, Gastón Keller <gastonkeller(a)gmail.com&gt;
>  wrote:
> >
> > Hello, everybody. I have been struggling with Xen's documentation
> > lately, not finding where to look for accurate and up-to-date info. I
> > remember having read in this list months ago someone saying that the
> > documentation was quite outdated. For example, the xm command _delete_
> > does not appear in the man pages and many guides still do reference to
> > the guest's config files being stored at /etc/xen (two days ago I
> > discovered that now Xen works in a different way).
> >
> > My objective is not only to learn how to use Xen, but understand how
> > it works. I'm doing my best looking for info in the net and going
> > through docs in the Xen Wiki, but I might be missing something in my
> > search. Therefore, I would really appreciate if someone could point me
> > to some documentation I should read, or whatever else you could think
> > of.
> >
> > Thanks,
> > Gaston
> >
> > --
> > La única verdad es la realidad.
> >
> > --
> > Fedora-xen mailing list
> > Fedora-xen(a)redhat.com
> > https://www.redhat.com/mailman/listinfo/fedora-xen
>
>
>
>  --
>  Emre 


-- 
La única verdad es la realidad.

[Emre Erenoglu]

Hmm,

On Fri, May 30, 2008 at 2:06 AM, Gastón Keller <gastonkeller(a)gmail.com&gt;
wrote:

>  On Thu, May 29, 2008 at 7:53 PM, Emre ERENOGLU
> <erenoglu(a)gmail.com&gt; wrote:
>  > Hi Gaston,
>  >
>  > It's true that some documentation is outdated. However, for the
>  "/etc/xen"
>  > isssue, my custom Xen 3.2 setup still stores ( and I do store there also)
>  my
>  > config files there.
>  >
>  > Maybe what you're saying is "Fedora Specific" which I could understand
> as
>  > it's fedora mailing list.
>
>  _The Fedora team has followed the Xensource model and begun to store
>  all VM configuration details in a database, referred to as xenstore._
>  Source:
>  http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...
>  
OK, I didn't know that. However, I find this xenstore thing a bit
complicated.


>  Then, you might be right. I interpreted it was a modification from
>  Xen, not from Fedora (previously introduced by Xensource). 

>  So, what is the advantage behind this movement? 

I think it's managegability.


>  Thanks,
>  Gaston
>
>   However, I never found the flexibility and control
>  > in the Fedora way of Xen implementation (all those xml stuff etc.).  most
>  > probably, I'm wrong :)
>  >
>  > Emre
>  >
>  > On Thu, May 29, 2008 at 9:22 PM, Gastón Keller <gastonkeller(a)gmail.com&gt;
>  > wrote:
>  >>
>  >> Hello, everybody. I have been struggling with Xen's documentation
>  >> lately, not finding where to look for accurate and up-to-date info. I
>  >> remember having read in this list months ago someone saying that the
>  >> documentation was quite outdated. For example, the xm command _delete_
>  >> does not appear in the man pages and many guides still do reference to
>  >> the guest's config files being stored at /etc/xen (two days ago I
>  >> discovered that now Xen works in a different way).
>  >>
>  >> My objective is not only to learn how to use Xen, but understand how
>  >> it works. I'm doing my best looking for info in the net and going
>  >> through docs in the Xen Wiki, but I might be missing something in my
>  >> search. Therefore, I would really appreciate if someone could point me
>  >> to some documentation I should read, or whatever else you could think
>  >> of.
>  >>
>  >> Thanks,
>  >> Gaston
>  >>
>  >> --
>  >> La única verdad es la realidad.
>  >>
>  >> --
>  >> Fedora-xen mailing list
>  >> Fedora-xen(a)redhat.com
>  >> https://www.redhat.com/mailman/listinfo/fedora-xen
>  >
>  >
>  >
>  > --
>  > Emre
>
>
>
>  --
>  La única verdad es la realidad.
>  


-- 
Emre

[Dustin Henning]

Emre,
	As you may already know, I still use the config files in /etc/xen and don’t mess with the
virsh stuff.  It all certainly worked fine in F7, and though I haven’t fully tested, it
appears that it all works fine in F8 as well.  I use them for one, because I learned with
them, and for two, because in the little time I have spent messing with the gui tools, I
haven't found near as much control.  That isn't to say that more can be done with
the old way, but instead to say that I can do more with the old way.  I don’t know if
there are any plans to deprecate that stuff, but I hope that if there ever are, news makes
the list before I end up on a version where I have no clue how to do anything!
	Dustin

From: fedora-xen-bounces(a)redhat.com [mailto:[e-mail]] On Behalf Of
Emre ERENOGLU
Sent: Friday, May 30, 2008 04:30
To: Gastón Keller
Cc: fedora-xen(a)redhat.com
Subject: Re: [Fedora-xen] Xen Documentation

Hmm,
On Fri, May 30, 2008 at 2:06 AM, Gastón Keller <gastonkeller(a)gmail.com&gt; wrote:
On Thu, May 29, 2008 at 7:53 PM, Emre ERENOGLU <erenoglu(a)gmail.com&gt; wrote:
>  Hi Gaston,
>
>  It's true that some documentation is outdated. However, for the "/etc/xen"
>  isssue, my custom Xen 3.2 setup still stores ( and I do store there also) my
>  config files there.
>
>  Maybe what you're saying is "Fedora Specific" which I could understand as
>  it's fedora mailing list. 
_The Fedora team has followed the Xensource model and
begun to store
all VM configuration details in a database, referred to as xenstore._
Source:
http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...

OK, I didn't know that. However, I find this xenstore thing a bit complicated.

Then, you might be right. I interpreted it was a modification from
Xen, not from Fedora (previously introduced by Xensource). 

So, what is the advantage behind this movement?

I think it's managegability. 


Thanks,
Gaston

 However, I never found the flexibility and control
>  in the Fedora way of Xen implementation (all those xml stuff etc.). 
> most
>  probably, I'm wrong :)
>
>  Emre
>
>  On Thu, May 29, 2008 at 9:22 PM, Gastón Keller <gastonkeller(a)gmail.com&gt;
>  wrote:
> >
> > Hello, everybody. I have been struggling with Xen's documentation
> > lately, not finding where to look for accurate and up-to-date info. I
> > remember having read in this list months ago someone saying that the
> > documentation was quite outdated. For example, the xm command _delete_
> > does not appear in the man pages and many guides still do reference to
> > the guest's config files being stored at /etc/xen (two days ago I
> > discovered that now Xen works in a different way).
> >
> > My objective is not only to learn how to use Xen, but understand how
> > it works. I'm doing my best looking for info in the net and going
> > through docs in the Xen Wiki, but I might be missing something in my
> > search. Therefore, I would really appreciate if someone could point me
> > to some documentation I should read, or whatever else you could think
> > of.
> >
> > Thanks,
> > Gaston
> >
> > --
> > La única verdad es la realidad.
> >
> > --
> > Fedora-xen mailing list
> > Fedora-xen(a)redhat.com
> > https://www.redhat.com/mailman/listinfo/fedora-xen
>
>
>
>  --
>  Emre 

--
La única verdad es la realidad.



-- 
Emre

[Daniel P. Berrange]

On Thu, May 29, 2008 at 08:06:32PM -0400, Gast?n Keller wrote:
>  On Thu, May 29, 2008 at 7:53 PM, Emre ERENOGLU
> <erenoglu(a)gmail.com&gt; wrote:
>  > Hi Gaston,
>  >
>  > It's true that some documentation is outdated. However, for the
> "/etc/xen"
>  > isssue, my custom Xen 3.2 setup still stores ( and I do store there also) my
>  > config files there.
>  >
>  > Maybe what you're saying is "Fedora Specific" which I could understand
> as
>  > it's fedora mailing list.
>  
>  _The Fedora team has followed the Xensource model and begun to store
>  all VM configuration details in a database, referred to as xenstore._ 
No, xenstore only holds information about active VMs. The persistent VM config
is managed by XenD itself, and stored in files under /var/lib/xend.

>  Source:
> http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...
>  
>  Then, you might be right. I interpreted it was a modification from
>  Xen, not from Fedora (previously introduced by Xensource). 
This was all implemented by upstream Xen. Libvirt probes for this capability
in XenD and if it finds it, it will make use of it, since libvirt wants to
be able to manage inactive VMs too. Since Fedora 7 was the first to ship
this capability in Xen, it was the first release where libvirt would enable
this inactive domain management.
 
>  So, what is the advantage behind this movement? 
The key reason for this was to allow XenD the ability to manage inactive
domains. So all its APIs for modifying VM configs now work for running
and inactive VMs. This is impossible for XenD if using /etc/xen. This is
why 'xm list' won't show you configs stored in /etc/xen.

Dan.
-- 
|: Red Hat, Engineering, Boston   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|

[Emre Erenoglu]

Yes, but I don't have the same flexibility of options in the libvirt
implementation.

Emre

On Fri, May 30, 2008 at 2:32 PM, Daniel P. Berrange <berrange(a)redhat.com&gt;
wrote:

>  On Thu, May 29, 2008 at 08:06:32PM -0400, Gast?n Keller wrote:
>  > On Thu, May 29, 2008 at 7:53 PM, Emre ERENOGLU <erenoglu(a)gmail.com&gt;
>  wrote:
>  > > Hi Gaston,
>  > >
>  > > It's true that some documentation is outdated. However, for the
>  "/etc/xen"
>  > > isssue, my custom Xen 3.2 setup still stores ( and I do store there
>  also) my
>  > > config files there.
>  > >
>  > > Maybe what you're saying is "Fedora Specific" which I could
> understand
>  as
>  > > it's fedora mailing list.
>  >
>  > _The Fedora team has followed the Xensource model and begun to store
>  > all VM configuration details in a database, referred to as xenstore._
>
>  No, xenstore only holds information about active VMs. The persistent VM
>  config
>  is managed by XenD itself, and stored in files under /var/lib/xend.
>
>  > Source:
>  http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...
>  >
>  > Then, you might be right. I interpreted it was a modification from
>  > Xen, not from Fedora (previously introduced by Xensource).
>
>  This was all implemented by upstream Xen. Libvirt probes for this
>  capability
>  in XenD and if it finds it, it will make use of it, since libvirt wants to
>  be able to manage inactive VMs too. Since Fedora 7 was the first to ship
>  this capability in Xen, it was the first release where libvirt would enable
>  this inactive domain management.
>
>  > So, what is the advantage behind this movement?
>
>  The key reason for this was to allow XenD the ability to manage inactive
>  domains. So all its APIs for modifying VM configs now work for running
>  and inactive VMs. This is impossible for XenD if using /etc/xen. This is
>  why 'xm list' won't show you configs stored in /etc/xen.
>
>  Dan.
>  --
>  |: Red Hat, Engineering, Boston   -o-   http://people.redhat.com/berrange/:|
>  |: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org:|
>  |: http://autobuild.org       -o-        
> http://search.cpan.org/~danberr/<http://search.cpan.org/%7Edanberr/>:|
>  |: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505
>  :|
>  


-- 
Emre

[Ian Jackson]

Gastón Keller writes ("Re: [Fedora-xen] Xen Documentation"):
>  _The Fedora team has followed the Xensource model and begun to store
>  all VM configuration details in a database, referred to as xenstore._
>  Source:
> http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi... 
I wouldn't believe everything you read on the internet :-).

Open Source Xen doesn't store configuration details in a database.  It
uses plain text configuration files in /etc.  To a limited amount
information about xend-managed domains is stored in /var in what is
arguably a kind of database, but not in xenstore.

Xenstore is not a database containing configuration details; it is
cleared out at reboot.  The name is misleading; the earlier name
`xenbus' is clearer: xenstore is used as an inter-component
communication mechanism, for communicating between the various
non-hypervisor components of a running system, and particularly for
advertising devices to paravirtualised guests.

As I understand it, the proprietary XenSource XenServer product does
indeed keep much in a database but that database is not xenstore.
(But I don't really work on the proprietary side so I may be wrong.)

I don't know what, if anything, is changing in Fedora.  It's difficult
to tell from that blog posting.  Perhaps some of the Fedora guys here
on this list can enlighten us; otherwise ask on fedora-xen ?

Ian.

[Daniel P. Berrange]

On Fri, May 30, 2008 at 02:51:18PM +0100, Ian Jackson wrote:
>  Gastón Keller writes ("Re: [Fedora-xen] Xen
> Documentation"):
>  > _The Fedora team has followed the Xensource model and begun to store
>  > all VM configuration details in a database, referred to as xenstore._
>  > Source:
> http://enterpriselinuxlog.blogs.techtarget.com/2007/06/07/fedora-7-xen-fi...
>  
>  I wouldn't believe everything you read on the internet :-).
>  
>  Open Source Xen doesn't store configuration details in a database.  It
>  uses plain text configuration files in /etc.  To a limited amount
>  information about xend-managed domains is stored in /var in what is
>  arguably a kind of database, but not in xenstore. 
Or it uses text files in /var/lib/xen for domain configs.

>  I don't know what, if anything, is changing in Fedora.  It's
> difficult
>  to tell from that blog posting.  Perhaps some of the Fedora guys here
>  on this list can enlighten us; otherwise ask on fedora-xen ? 
We haven't changed anything in Xen in this regard. In Xen 3.0.3 and
ealier the only place to store config files was in /etc, and XenD had
no concept of inactive domains. In Xen 3.0.4 or later, XenD can directly
manage inactive domains, storing their configs in /var/lib/xen/. IF
libvirt detects a new enough XenD it will use its inactive domain
management capabilities instead of putting configs in /etc, since this
gives access to a greater level of functionality.

Dan.
-- 
|: Red Hat, Engineering, Boston   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|

[Ian Jackson]

Daniel P. Berrange writes ("Re: [Fedora-xen] Xen Documentation"):
>  On Fri, May 30, 2008 at 02:51:18PM +0100, Ian Jackson wrote:
>  > Open Source Xen doesn't store configuration details in a database.  It
>  > uses plain text configuration files in /etc.  To a limited amount
>  > information about xend-managed domains is stored in /var in what is
>  > arguably a kind of database, but not in xenstore.
>  
>  Or it uses text files in /var/lib/xen for domain configs. 
Right, that's what I meant.

>  > I don't know what, if anything, is changing in Fedora. 
> It's difficult
>  > to tell from that blog posting.  Perhaps some of the Fedora guys here
>  > on this list can enlighten us; otherwise ask on fedora-xen ?
>  
>  We haven't changed anything in Xen in this regard. In Xen 3.0.3 and
>  ealier the only place to store config files was in /etc, and XenD had
>  no concept of inactive domains. In Xen 3.0.4 or later, XenD can directly
>  manage inactive domains, storing their configs in /var/lib/xen/. IF
>  libvirt detects a new enough XenD it will use its inactive domain
>  management capabilities instead of putting configs in /etc, since this
>  gives access to a greater level of functionality. 
That sounds sensible.  I'm not sure how that relates to the blog
posting mentioned by the original poster.

Ian.

[Daniel P. Berrange]

On Fri, May 30, 2008 at 03:18:57PM +0100, Ian Jackson wrote:
>  Daniel P. Berrange writes ("Re: [Fedora-xen] Xen
> Documentation"):
>  > On Fri, May 30, 2008 at 02:51:18PM +0100, Ian Jackson wrote:
>  > > Open Source Xen doesn't store configuration details in a database.  It
>  > > uses plain text configuration files in /etc.  To a limited amount
>  > > information about xend-managed domains is stored in /var in what is
>  > > arguably a kind of database, but not in xenstore.
>  > 
>  > Or it uses text files in /var/lib/xen for domain configs.
>  
>  Right, that's what I meant.
>  
>  > > I don't know what, if anything, is changing in Fedora.  It's difficult
>  > > to tell from that blog posting.  Perhaps some of the Fedora guys here
>  > > on this list can enlighten us; otherwise ask on fedora-xen ?
>  > 
>  > We haven't changed anything in Xen in this regard. In Xen 3.0.3 and
>  > ealier the only place to store config files was in /etc, and XenD had
>  > no concept of inactive domains. In Xen 3.0.4 or later, XenD can directly
>  > manage inactive domains, storing their configs in /var/lib/xen/. IF
>  > libvirt detects a new enough XenD it will use its inactive domain
>  > management capabilities instead of putting configs in /etc, since this
>  > gives access to a greater level of functionality.
>  
>  That sounds sensible.  I'm not sure how that relates to the blog
>  posting mentioned by the original poster. 
That posting is mostly based on a mis-understanding of what XenD is doing,
but also the fact that there is no way to get the config back out of XenD
using 'xm'. ie, you can load a traditional /etc/xen style config into XenD
using 'xm new CONFIG', but you can't ask XenD to generate you a traditional
style cofnig for one of the VMs its managing. Not an issue if you're using
libvirt for management, since it doesn't use /etc/xen style configs anyway.
While, there are a few people who need to use /etc/xen configs to get access
to specific features not supported in libvirt (PCI device passthrough), they
are a small niche.  On the whole switching to using the new inactive domain
management APIs in XenD was a net-win, with the benefits far outweighing
the disadvantages.

Dan.
-- 
|: Red Hat, Engineering, Boston   -o-   http://people.redhat.com/berrange/ :|
|: http://libvirt.org  -o-  http://virt-manager.org  -o-  http://ovirt.org :|
|: http://autobuild.org       -o-         http://search.cpan.org/~danberr/ :|
|: GnuPG: 7D3B9505  -o-  F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 :|

[Aaron Metzger]

Daniel P. Berrange wrote:

>  
>  That posting is mostly based on a mis-understanding of what XenD is doing,
>  but also the fact that there is no way to get the config back out of XenD
>  using 'xm'. ie, you can load a traditional /etc/xen style config into XenD
>  using 'xm new CONFIG', but you can't ask XenD to generate you a traditional
>  style cofnig for one of the VMs its managing. Not an issue if you're using
>  libvirt for management, since it doesn't use /etc/xen style configs anyway.
>  While, there are a few people who need to use /etc/xen configs to get access
>  to specific features not supported in libvirt (PCI device passthrough), they
>  are a small niche.  On the whole switching to using the new inactive domain
>  management APIs in XenD was a net-win, with the benefits far outweighing
>  the disadvantages.
>   
Can we mix and match.  Can we have some old style configs in "/etc/xen" 
for some guests while using libvirt for the rest?

I'm using the new way of doing things now but wonder what will happen if 
some day I need PCI device passthrough for one guest.  Do, I have to 
revert all guests back to the old style of config to have this 
capability for one?