[Xen-devel] Re: [RFC] "xs_read(): uuid get error" of qemu-dm

[Masami Watanabe <masami.watanabe@xxxxxxxxxxxxxx>]

Hi Keir,

My explanation was insufficient.

"xs_read(): uuid get error" happens when uuid can't read from xenstore
in xenstore_read_vncpasswd@tools/ioemu/xenstore.c.

c/s 12187 evaded this problem when the guest rebooted in a lot of
environments. As for my environment, the problem was corrected by this
correction.

However, Afterwards, following problem keeps happening.
I think that it is a problem.

[Xen-devel] VMX status report 12254:f8ffeb540ec1
  http://lists.xensource.com/archives/html/xen-devel/2006-11/msg00288.html
[Xen-devel] VMX status report 12217:20204db0891b
  http://lists.xensource.com/archives/html/xen-devel/2006-11/msg00183.html
>  IA32/PAE/IA32E: Windows and Linux VMX domains may fail to be
> created, the qemu-dm process is <defunct>, and the qemu log says
> "xs_read(): uuid get error."


I examined it.
As a result, In the environment that allocated two or more CPU in
Dom0, this problem was able to be caused.
The result of the confirmation is as follows.
- uuid cannot be read with xenstore_read_vncpasswd() in qemu-dm.
- uuid can often be read by changing the order of vm.initDomain()
  and vm.storeVmDetails() in create()@XendDomainInfo.py.
- And, when the read timing is delayed in qemu-dm, It was possible
  to always read.

>From the above, I thought that this problem was a problem of the timing
of writing and reading to xenstore from another process.


> Is the passwd getting written after qemu
> is started and hence racing the xs_read() in xenstored?

Yes, maybe. I understand the order of processing xend as follows.
Is it my misunderstanding ?

  create()@XendDomainInfo.py+135
      start()
          _initDomain()
              _createDevices()
                  createDeviceModel(self)@image.py
                      os.spawnve()  ==============>  start qemu-dm process
          _storeVmDetails()
              _writeVm()            ==============>  write to xenstore
              _setVmPermissions()


Masami



On Tue, 07 Nov 2006 08:18:44 +0000, Keir Fraser wrote:
> On 7/11/06 3:46 am, "Masami Watanabe" <masami.watanabe@xxxxxxxxxxxxxx>
> wrote:
> 
> > since c/s 11840, qemu-dm process is <defunct>, and the qemu log says
> > "xs_read(): uuid get error" in guest reboot.
> > This is because of being not able to read yet when qemu-dm reads
> > vncpasswd from xenstore.
> > (xend has spawned qemu-dm before writing vncpasswd to xenstore)
> 
> This was supposed to be fixed by c/s 12187.
> 
> If it hasn't, we need to fix xend to write the passwd before starting qemu,
> and/or qemu needs to treat failure of the xs_read() as an indication that
> there is no authentication.
> 
> What do you think is the problem? Is the passwd getting written after qemu
> is started and hence racing the xs_read() in xenstored?
> 
> We don't want to work around this with a timeouts.
> 
>  -- Keir




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