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[Xen-users] Error: Device 769 (vbd) could not be connected... Limit of 2

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Error: Device 769 (vbd) could not be connected... Limit of 25 domains.
From: Thomas Karsten <thomas@xxxxxxxxxxx>
Date: Wed, 19 Jul 2006 18:18:34 +0800
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Hello,

I am running Xen 3.0.2 in an Ubuntu 6.06 Linux system (kernel 2.6.16-xen). 
Xend is running and works well.

I would like to use Xen to run about 80 domains (for testing purpose). All 
domains share the same image file (which therefor is mounted 'readonly' by 
Xen) and each domain is configured to use only 10 MB of RAM. I am using a 
script to generate name, hostname and IP address for each guest (it simply 
loops over i and calls:'xm create name=guestdom$i hostname=$i ip=192.168.1.
$i').

Everything works fine, but after 25 concurrent running domains Xen refuses to 
create any further domains, giving me the error:

Error: Device 769 (vbd) could not be connected. Hotplug scripts not working.

On this mailing list I found several threads dealing with this error message. 
However, I did not find that anybody is facing this kind of limitation that I 
have. For your information, the number of loopback devices in my system is 
132. Also, I am not running out of memory, this would be stated by Xen (I 
have 1500 MB of RAM, where 500 MB are occupied by Xen).

I can remove a guest domain and create a new one, this is no problem. However, 
on my system I am not able to create more than 25 domains at the same time. 
Can anybody help please?

Thank you very much, all ideas are appreciated,
Thomas

----------------------------------------
Output of Xen below:

# xm info
host                   : pc27
release                : 2.6.16-xen
version                : #1 SMP Thu Jul 13 10:04:57 CST 2006
machine                : x86_64
nr_cpus                : 2
nr_nodes               : 1
sockets_per_node       : 1
cores_per_socket       : 1
threads_per_core       : 2
cpu_mhz                : 3000
hw_caps                : bfebfbff:20100800:00000000:00000180:0000641d
total_memory           : 1510
free_memory            : 722
xen_major              : 3
xen_minor              : 0
xen_extra              : .2-2
xen_caps               : xen-3.0-x86_64
platform_params        : virt_start=0xffff800000000000
xen_changeset          : Thu Apr 13 15:18:37 2006 +0100 9617:5802713c159b
cc_compiler            : gcc version 4.0.3 (Ubuntu 4.0.3-1ubuntu5)
cc_compile_by          : root
cc_compile_domain      : 
cc_compile_date        : Thu Jul 13 11:12:54 CST 2006

----------

# xm list
Name                              ID Mem(MiB) VCPUs State  Time(s)
Domain-0                           0      508     2 r-----  1092.8
guestdom120                       71       10     1 ------     2.3
guestdom121                       72       10     1 ------     2.4
guestdom122                       73       10     1 ------     1.8
guestdom123                       74       10     1 ------     1.8
guestdom124                       75       10     1 ------     1.8
guestdom125                       76       10     1 ------     1.8
guestdom126                       77       10     1 ------     2.2
guestdom127                       78       10     1 ------     1.8
guestdom128                       79       10     1 ------     1.8
guestdom129                       80       10     1 ------     1.7
guestdom130                       81       10     1 ------     1.7
guestdom131                       82       10     1 ------     1.7
guestdom132                       83       10     1 ------     1.7
guestdom133                       84       10     1 ------     1.7
guestdom134                       85       10     1 ------     1.7
guestdom135                       86       10     1 ------     1.7
guestdom136                       87       10     1 ------     1.7
guestdom137                       88       10     1 ------     1.7
guestdom138                       89       10     1 ------     1.7
guestdom139                       90       10     1 ------     1.7
guestdom140                       91       10     1 ------     1.7
guestdom141                       92       10     1 ------     1.6
guestdom142                       93       10     1 ------     1.6
guestdom143                       94       10     1 ------     1.6
guestdom144                       95       10     1 ------     1.6

----------
My config file for each domU looks like this:

#
# base settings
#
kernel = "/boot/vmlinuz-2.6.16-xenU"
memory = 10
name = "guestdom1"
disk = ['file:/xen-images/guestdom1.img,hda1,ro']

#
# network settings:
# change the ip address for each guest
#
vif = ['bridge=xenbr0']
ip = "192.168.1.120"
netmask = "255.255.255.0"
gateway = "192.168.1.1"
hostname = name
root = "/dev/hda1 rw"

----------
The content of xend.log (for one failed creation):

[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:178) 
XendDomainInfo.create(['vm', ['name', 'guestdom145'], ['memory', 10], 
['vcpus', 1], ['image', ['linux', ['kernel', '/boot/vmlinuz-2.6.16-xenU'], 
['ip', '192.168.1.141:1.2.3.4:192.168.1.1:255.255.255.0:guestdom1:eth0:off'], 
['root', '/dev/hda1 rw']]], ['device', ['vbd', ['uname', 
'file:/xen-images/guestdom1.img'], ['dev', 'hda1'], ['mode', 'ro']]], 
['device', ['vif', ['bridge', 'xenbr0']]]])
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:284) 
parseConfig: config is ['vm', ['name', 'guestdom145'], ['memory', 10], 
['vcpus', 1], ['image', ['linux', ['kernel', '/boot/vmlinuz-2.6.16-xenU'], 
['ip', '192.168.1.141:1.2.3.4:192.168.1.1:255.255.255.0:guestdom1:eth0:off'], 
['root', '/dev/hda1 rw']]], ['device', ['vbd', ['uname', 
'file:/xen-images/guestdom1.img'], ['dev', 'hda1'], ['mode', 'ro']]], 
['device', ['vif', ['bridge', 'xenbr0']]]]
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:380) 
parseConfig: result is {'ssidref': None, 'uuid': None, 'on_crash': None, 
'on_reboot': None, 'image': ['linux', ['kernel', 
'/boot/vmlinuz-2.6.16-xenU'], ['ip', 
'192.168.1.141:1.2.3.4:192.168.1.1:255.255.255.0:guestdom1:eth0:off'], 
['root', '/dev/hda1 rw']], 'on_poweroff': None, 'cpus': None, 'name': 
'guestdom145', 'backend': [], 'vcpus': 1, 'cpu_weight': None, 'vcpu_avail': 
None, 'memory': 10, 'device': [('vbd', ['vbd', ['uname', 
'file:/xen-images/guestdom1.img'], ['dev', 'hda1'], ['mode', 'ro']]), ('vif', 
['vif', ['bridge', 'xenbr0']])], 'bootloader': None, 'cpu': None, 'maxmem': 
None}
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:1164) 
XendDomainInfo.construct: None 0
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:1196) 
XendDomainInfo.initDomain: 96 1.0
[2006-07-19 18:02:46 xend] DEBUG (balloon:126) Balloon: free 718; need 11; 
done.
[2006-07-19 18:02:46 xend] INFO (image:135) buildDomain os=linux dom=96 
vcpus=1
[2006-07-19 18:02:46 xend] DEBUG (image:173) dom            = 96
[2006-07-19 18:02:46 xend] DEBUG (image:174) image          
= /boot/vmlinuz-2.6.16-xenU
[2006-07-19 18:02:46 xend] DEBUG (image:175) store_evtchn   = 1
[2006-07-19 18:02:46 xend] DEBUG (image:176) console_evtchn = 2
[2006-07-19 18:02:46 xend] DEBUG (image:177) cmdline        =  
ip=192.168.1.141:1.2.3.4:192.168.1.1:255.255.255.0:guestdom1:eth0:off 
root=/dev/hda1 rw
[2006-07-19 18:02:46 xend] DEBUG (image:178) ramdisk        = 
[2006-07-19 18:02:46 xend] DEBUG (image:179) vcpus          = 1
[2006-07-19 18:02:46 xend] DEBUG (image:180) features       = 
[2006-07-19 18:02:46 xend] DEBUG (blkif:24) exception looking up device number 
for hda1: [Errno 2] No such file or directory: '/dev/hda1'
[2006-07-19 18:02:46 xend] DEBUG (DevController:103) DevController: writing 
{'virtual-device': '769', 'backend-id': '0', 'state': '1', 'backend': 
'/local/domain/0/backend/vbd/96/769'} to /local/domain/96/device/vbd/769.
[2006-07-19 18:02:46 xend] DEBUG (DevController:105) DevController: writing 
{'domain': 'guestdom145', 'frontend': '/local/domain/96/device/vbd/769', 
'dev': 'hda1', 'state': '1', 'params': '/xen-images/guestdom1.img', 'mode': 
'ro', 'frontend-id': '96', 'type': 'file'} 
to /local/domain/0/backend/vbd/96/769.
[2006-07-19 18:02:46 xend] DEBUG (DevController:103) DevController: writing 
{'backend-id': '0', 'mac': '00:16:3e:29:bf:6a', 'handle': '0', 'state': '1', 
'backend': '/local/domain/0/backend/vif/96/0'} 
to /local/domain/96/device/vif/0.
[2006-07-19 18:02:46 xend] DEBUG (DevController:105) DevController: writing 
{'bridge': 'xenbr0', 'domain': 'guestdom145', 'handle': '0', 'script': 
'/etc/xen/scripts/vif-bridge', 'state': '1', 'frontend': 
'/local/domain/96/device/vif/0', 'mac': '00:16:3e:29:bf:6a', 'frontend-id': 
'96'} to /local/domain/0/backend/vif/96/0.
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:671) Storing 
VM details: {'ssidref': '0', 'uuid': '7fcd771f-3975-8798-9656-225555b52bd2', 
'on_reboot': 'restart', 'start_time': '1153303366.78', 'on_poweroff': 
'destroy', 'name': 'guestdom145', 'vcpus': '1', 'vcpu_avail': '1', 'memory': 
'10', 'on_crash': 'restart', 'image': "(linux 
(kernel /boot/vmlinuz-2.6.16-xenU) (ip 
192.168.1.141:1.2.3.4:192.168.1.1:255.255.255.0:guestdom1:eth0:off) (root 
'/dev/hda1 rw'))", 'maxmem': '10'}
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:696) Storing 
domain details: {'console/ring-ref': '325704', 'console/port': '2', 'name': 
'guestdom145', 'console/limit': '1048576', 'vm': 
'/vm/7fcd771f-3975-8798-9656-225555b52bd2', 'domid': '96', 
'cpu/0/availability': 'online', 'memory/target': '10240', 'store/ring-ref': 
'325705', 'store/port': '1'}
[2006-07-19 18:02:46 xend.XendDomainInfo] DEBUG (XendDomainInfo:877) 
XendDomainInfo.handleShutdownWatch
[2006-07-19 18:02:47 xend] DEBUG (DevController:132) Waiting for devices vif.
[2006-07-19 18:02:47 xend] DEBUG (DevController:138) Waiting for 0.
[2006-07-19 18:02:47 xend] DEBUG (DevController:403) 
hotplugStatusCallback /local/domain/0/backend/vif/96/0/hotplug-status.
[2006-07-19 18:02:47 xend] DEBUG (DevController:403) 
hotplugStatusCallback /local/domain/0/backend/vif/96/0/hotplug-status.
[2006-07-19 18:02:47 xend] DEBUG (DevController:417) hotplugStatusCallback 1.
[2006-07-19 18:02:47 xend] DEBUG (DevController:132) Waiting for devices usb.
[2006-07-19 18:02:47 xend] DEBUG (DevController:132) Waiting for devices vbd.
[2006-07-19 18:02:47 xend] DEBUG (DevController:138) Waiting for 769.
[2006-07-19 18:02:47 xend] DEBUG (DevController:403) 
hotplugStatusCallback /local/domain/0/backend/vbd/96/769/hotplug-status.
[2006-07-19 18:02:57 xend.XendDomainInfo] DEBUG (XendDomainInfo:1327) 
XendDomainInfo.destroy: domid=96
[2006-07-19 18:02:57 xend.XendDomainInfo] DEBUG (XendDomainInfo:1335) 
XendDomainInfo.destroyDomain(96)

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