Configuration parameters get "sometimes" omitted

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

Hi,
we have the problem that our xen configuration settings are not correctly evaluated when creating a xen guests.

When creating domains with "xm create domainname" the system sometimes has all configuration parameters out of the config files, but sometimes not.
We did some tests and saw that the parameters are only certainly used if we specify them via the commandline like "xm create domainname parameter=value,...".

If the parameters are only specified in the configuration files in /etc/xen/ they are parsed and used "sometimes".
Another fact we found is that if the "xm create" is called by a script the error occurs very often ~70% of the testcases, while calling the command from a ssh shell manually only fails in ~10% of the testcases. We stripped down the script and it does nothing but calling "xm create" and the normal shell where it works mostly has no .profile/.bashrc/... that change the environment.
Additionally there is some persistent behavior - if it failed once it will fail until the host is rebooted (maybe some config parts are stored and not re-evaluated). I checked xenstore with the script from http://wiki.xensource.com/xenwiki/XenStore and saw that xenstore only has the parameters if a good-case guest is running.

An interesting fact is that it does not fail initializing memory or pci passthrough in host or guest - somehow it fails the initial config parsing. You can see below that already the output of XendDomainInfo.create in the log is different in good/bad case.

Because of the unstable behavior I expect some kind of race condition while parsing from the files.



### See below for more verbose details on what we found in the log's ,system setup and configuration files ###



The command "xm create lnudb1 pci=04:01.0 memory=2048" works always successful.
A "xm create lnudb1" creates only *sometimes* a system with a pci adapter and 2 GB memory.
Looking in the /var/log/xend.log reveals a different XendDomainInfo.create statement 
for good and bad case.

(I added the >>> <<< signs to point to the important statement)

XendDomainInfo.create(['vm', ['name', 'lnudb1'], ['memory', 2048], ['vcpus', 1], 
['on_xend_start', 'ignore'], ['on_xend_stop', 'ignore'], ['image', ['linux', 
['kernel', '/etc/xen/vmlinuz-xen'], ['ramdisk', '/etc/xen/initrd-xen'], ['root', '/dev/xvda1'], 
['args', 'TERM=xterm selinux=off xencons=tty']]], ['device', ['vbd', ['uname', 'phy:sde5'], 
['dev', 'xvda1'], ['mode', 'w']]], ['device', ['vbd', ['uname', 'phy:/dev/hda'], ['dev', 'hdc:cdrom'], 
['mode', 'r']]], 
>>> ['device', ['pci', ['dev', ['domain', '0x0'], ['bus', '0x04'], ['slot', '0x01'], ['func', '0x0']]]], <<<
['device', ['vif', ['bridge', 'xenbr0'], ['mac', '00:16:3e:00:00:10']]], ['device', ['vif', ['bridge', 'xenbr1'],
['mac', '00:16:3e:00:00:31']]], ['device', ['vkbd']], ['device', ['vfb', ['vncunused', '1'], ['type', 'vnc'],
['display', 'localhost:10.0'], ['xauthority', '/root/.Xauthority']]]])


The xm create with the profile described above produces following statement 
XendDomainInfo.create(['vm', ['name', 'lnudb1'], ['memory', 1024], ['vcpus', 1], 
['on_xend_start', 'ignore'], ['on_xend_stop', 'ignore'], ['image', ['linux', 
['kernel', '/etc/xen/vmlinuz-xen'], ['ramdisk', '/etc/xen/initrd-xen'], ['root', '/dev/xvda1'], 
['args', 'TERM=xterm selinux=off xencons=tty']]], ['device', ['vbd', ['uname', 'phy:sde5'], 
['dev', 'xvda1'], ['mode', 'w']]], ['device', ['vbd', ['uname', 'phy:/dev/hda'], ['dev', 'hdc:cdrom'], 
['mode', 'r']]], 
>>>  <<<<
['device', ['vif', ['bridge', 'xenbr0'], ['mac', '00:16:3e:00:00:10']]], ['device', ['vif', ['bridge', 'xenbr1'],
['mac', '00:16:3e:00:00:31']]], ['device', ['vkbd']], ['device', ['vfb', ['vncunused', '1'], ['type', 'vnc'],
['display', 'localhost:10.0'], ['xauthority', '/root/.Xauthority']]]])

Also note the different values for the memory statement

System Description
Hardware IBM x3950, 4 Intel Xeon CPUs (dual core) 3.5GHz, 23Gb memory.
The operating system is Linux SLES10 SP1, with the following rpms:
o xen-kmp-smp-3.1.0_2.6.16.46_0.12-0.1
o xen-libs-32bit-3.0.4_13138-0.40
o xen-doc-pdf-3.1.0-0.1
o kernel-xen-2.6.16.46-0.12
o xen-3.1.0-0.1
o xen-tools-3.1.0-0.1
o xen-doc-html-3.1.0-0.1
o xen-libs-3.1.0-0.1
o xen-tools-ioemu-3.1.0-0.1

the kernel is booted with the parameters 
pciback.hide=(04:01.0)(04:01.1)(06:01.0)(06:01.1)(08:01.0)(08:01.1) 
and /etc/modprobe.conf constains the statements 
install lpfc /sbin/modprobe pciback ; /sbin/modprobe --first-time --ignore-install lpfc
options  pciback hide=(04:01.0)(04:01.1)(06:01.0)(06:01.1)(08:01.0)(08:01.1)
to hide the pci adapters for the Dom0.

The xen profile used is:
builder='linux'
memory = 2048
name = "lnudb1"
vcpus = 1
vif = [ 'mac=00:16:3e:00:00:10, bridge=xenbr0', 'mac=00:16:3e:00:00:31, bridge=xenbr1' ]
disk = [ 'phy:sde5,xvda1,w', 'phy:/dev/hda,hdc:cdrom,r' ]
root = "/dev/xvda1"
extra = "TERM=xterm selinux=off xencons=tty"
vfb=[ "type=vnc,vncunused=1" ]
pci= [ '0000:04:01.0' ]

The critical parameters are memory and pci, we never saw the issue with e.g. vif's.

P.S. It was hard to decide between xen-devel and xen-users by topic for that mail.
Eventually I coose xen-devel becasue I'm already member of this list and thereby get also responses that may lack a cc to me. Please redirect if needed.

-- 

Grüsse / regards, 
Christian Ehrhardt

IBM Linux Technology Center, Open Virtualization
+49 7031/16-3385
Ehrhardt@linux.vnet.ibm.com
Ehrhardt@de.ibm.com

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