libvirt users - Aug 2019 - Re: Detach disk from VM - virsh (working) vs. PHP (not working)

Thank you for your help!

1, i used vda as install disk and vdb as target disk, because i boot from the
first. After setup boot order flag i was able change install disk to vdb and
target disk to vda. With this configuration when i boot from vdb i can install
OS with grub and after it redefine XML without vdb without problem. Thanks a
lot.

2, maybe i have something wrong, but still not working:

Now in libvirt log i got error: device not found: no target device vdb

but:

from VPS:

root@debian:~# ls /dev/vd*
/dev/vda  /dev/vda1  /dev/vdb  /dev/vdb1

from XML (virsh dumpxml):

    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/users/debian-test2.img'/>
      <backingStore/>
      <target dev='vda' bus='virtio'/>
      <alias name='virtio-disk0'/>
      <address type='pci' domain='0x0000' bus='0x01'
slot='0x00' function='0x0'/>
    </disk>
    <disk type='file' device='disk'>
      <driver name='qemu' type='qcow2'/>
      <source file='/users/debian-test2-install.img'/>
      <backingStore/>
      <target dev='vdb' bus='virtio'/>
      <boot order='1'/>
      <alias name='virtio-disk1'/>
      <address type='pci' domain='0x0000' bus='0x04'
slot='0x00' function='0x0'/>
    </disk>

and from libvirt_domain_get_disk_devices($domain):

Array ( [0] => vda [1] => vdb [num] => 2 )

As you see, there is vdb device in all cases.

PHP code is very simple:

$server =
libvirt_connect("qemu+tls://".$ip.“:“.$port."/system",
false);
$domain = libvirt_domain_lookup_by_name($server, "debian-test2");
libvirt_domain_disk_remove($domain,"vdb");
print_r(libvirt_get_last_error());

res: Unable to detach disk
> 2. 8. 2019 v 14:15, Michal Privoznik <mprivozn@redhat.com>:
> 
> On 8/1/19 10:12 AM, Jan Horak wrote:
>> Hi all,
>> i created a script in PHP for create a virtual server with two QCOW2
discs … one is our system for installation and second is target system.
>> After successfully instalation (create a blank Debian system, prepare
all files and grub partitions) i need a restart virtual without a installation
disk.
>> If i use Virsh:
>> detach-disk --domain debian-test2 --persistent --target vda
>> reset debian-test2
>> everything works well.
>> If i use a PHP, there is „complicated“ way and „simple“ way:
>> 1, complicated:
>> libvirt_domain_destroy($domain);
>> libvirt_domain_undefine($domain);
>> $xml = domain_create_xml($name,$uuid,$memory,$cpu,$vnc,$mac);
>> $domain = libvirt_domain_define_xml($server->conn, $xml);
>> libvirt_domain_disk_add($domain,
"/users/".$name.".img", "vdb", "virtio",
"qcow2", NULL);
>> libvirt_domain_create($domain);
>> (or instead libvirt_domain_disk_add i can define disk directly in XML)
>> But in this case, the server will not boot (GRUB error)
> 
> Question is, how GRUB refers to the disk where kernel is to be found. Also,
I suspect it is not GRUB that is complaining, but SeaBIOS which hasn't found
any bootable device. It's only an assumption becasue I don't know how
domain_create_xml() works - it's not a libvirt-php function. There are two
possibilities here:
> 
> 1) make sure domain_create_xml() sets boot devices
> 2) construct disk XML yourself, and put "<boot
order='N'/>" into it
> 
>> 2, simple:
>> libvirt_domain_disk_remove($domain,“vda“);
>> libvirt_domain_reboot($domain);
>> The problem of this solution is thats not working. The remove disk is
failing with error „Unable attach disk“ - i looks to source code, and yes, there
is a mystake with „attach“/„detach“, but main problem i see in log from libvirt:
> 
> Oh, that's only typo in the error message. In fact the detach API is
called. And it fails.
> 
>> Aug  1 02:57:05 ry libvirtd[19051]: missing source information for
device vda
>> I try to put source detail to xml in source of PHP module
>> libvirt-domain.c:
>>   822	    if (asprintf(&newXml,
>>   823	                 "    <disk type='file'
device='disk'>\n"
>>   824	                 "      <target
dev='%s'/>\n"
>>   825	                 "    </disk>", dev) < 0) {
>>   826	        set_error("Out of memory" TSRMLS_CC);
>>   827	        goto error;
>>   828	    }
>> but my attempts was unsuccesfull (i’m not C programmer).
> 
> Yes, this minimalistic XML is not good as detach API requires full device
XML. I'll fix this soon.
> 
>> Questions:
>> A, why complicated way is not working and system dont want boot (GRUB
error) if virsh works fine
>> B, why libvirt_domain_disk_remove is not work ? I use libvirt and
libvirt-php latest from git.
> 
> I've pushed fixes here:
> 
> 
> Please give it a try.
> 
> Michal

On 8/2/19 6:26 PM, Jan Horak wrote:
> Thank you for your help!
> 
> 1, i used vda as install disk and vdb as target disk, because i boot from
the first. After setup boot order flag i was able change install disk to vdb and
target disk to vda. With this configuration when i boot from vdb i can install
OS with grub and after it redefine XML without vdb without problem. Thanks a
lot.
> 
> 2, maybe i have something wrong, but still not working:
> 
> Now in libvirt log i got error: device not found: no target device vdb
Ah, of coure. I overlooked that virDomainDetachDeviceFlags() is called
with VIR_DOMAIN_AFFECT_CONFIG, which means that live configuration is
not affected and if the disk you're trying to detach exists only in live
XML then the API fails. The same problem was found in
libvirt_domain_disk_add, libvirt_domain_nic_add and
libvirt_domain_nic_remove.

I've pushed the fixes to the master. Thanks for the report.

Michal

Hi, 

i confirm thats works very well now! Thank you for your support!

Jan
> 3. 8. 2019 v 8:54, Michal Prívozník <mprivozn@redhat.com>:
> 
> On 8/2/19 6:26 PM, Jan Horak wrote:
>> Thank you for your help!
>> 
>> 1, i used vda as install disk and vdb as target disk, because i boot
from the first. After setup boot order flag i was able change install disk to
vdb and target disk to vda. With this configuration when i boot from vdb i can
install OS with grub and after it redefine XML without vdb without problem.
Thanks a lot.
>> 
>> 2, maybe i have something wrong, but still not working:
>> 
>> Now in libvirt log i got error: device not found: no target device vdb
> 
> Ah, of coure. I overlooked that virDomainDetachDeviceFlags() is called
> with VIR_DOMAIN_AFFECT_CONFIG, which means that live configuration is
> not affected and if the disk you're trying to detach exists only in
live
> XML then the API fails. The same problem was found in
> libvirt_domain_disk_add, libvirt_domain_nic_add and
> libvirt_domain_nic_remove.
> 
> I've pushed the fixes to the master. Thanks for the report.
> 
> Michal