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Re: [libvirt] [PATCHv5 2/3] libvirt/qemu - support persistent modification of qemu disks



At 03/23/2011 01:22 PM, KAMEZAWA Hiroyuki Write:
> On Wed, 23 Mar 2011 13:15:39 +0800
> Wen Congyang <wency cn fujitsu com> wrote:
> 
>> At 03/23/2011 12:39 PM, KAMEZAWA Hiroyuki Write:
>>> On Mon, 21 Mar 2011 16:05:19 +0800
>>> Wen Congyang <wency cn fujitsu com> wrote:
>>>
>>>> At 03/16/2011 02:45 PM, KAMEZAWA Hiroyuki Write:
>>>>> >From ddcd9cb499dd73dfc91c9f2cc97c064d6dda17fc Mon Sep 17 00:00:00 2001
>>>>> From: KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com>
>>>>> Date: Wed, 16 Mar 2011 14:05:21 +0900
>>>>> Subject: [PATCHv5 2/3] libvirt/qemu - support persistent modification of qemu disks
>>>>>
>>>>> support changes of disks by VIR_DOMAIN_DEVICE_MODIFY_CONFIG
>>>>> for qemu.
>>>>>
>>>>> Changelog v4->v5:
>>>>>   - moved some functions to domain_conf.c
>>>>>   - added virDomainDefAddImplicitControllers() for ide/scsi
>>>>>   - report OOM.
>>>>>   - clean up.
>>>>>
>>>>> Signed-off-by: KAMEZAWA Hiroyuki <kamezawa hiroyu jp fujitsu com>
>>>>> ---
>>>>>  src/conf/domain_conf.c   |   22 ++++++++++++++++++++++
>>>>>  src/conf/domain_conf.h   |    3 ++-
>>>>>  src/libvirt_private.syms |    2 ++
>>>>>  src/qemu/qemu_driver.c   |   29 +++++++++++++++++++++++++++++
>>>>>  4 files changed, 55 insertions(+), 1 deletions(-)
>>>>>
>>>>> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
>>>>> index 16e1291..1d39481 100644
>>>>> --- a/src/conf/domain_conf.c
>>>>> +++ b/src/conf/domain_conf.c
>>>>> @@ -4859,6 +4859,19 @@ virVirtualPortProfileFormat(virBufferPtr buf,
>>>>>      virBufferVSprintf(buf, "%s</virtualport>\n", indent);
>>>>>  }
>>>>>  
>>>>> +int virDomainDiskIndexByName(virDomainDefPtr def, const char *name)
>>>>> +{
>>>>> +    virDomainDiskDefPtr vdisk;
>>>>> +    int i;
>>>>> +
>>>>> +    for (i = 0; i < def->ndisks; i++) {
>>>>> +        vdisk = def->disks[i];
>>>>> +        if (STREQ(vdisk->dst, name))
>>>>> +            return i;
>>>>> +    }
>>>>> +    return -1;
>>>>> +}
>>>>> +
>>>>>  int virDomainDiskInsert(virDomainDefPtr def,
>>>>>                          virDomainDiskDefPtr disk)
>>>>>  {
>>>>> @@ -4930,6 +4943,15 @@ void virDomainDiskRemove(virDomainDefPtr def, size_t i)
>>>>>      }
>>>>>  }
>>>>>  
>>>>> +int virDomainDiskRemoveByName(virDomainDefPtr def, const char *name)
>>>>> +{
>>>>> +    int i = virDomainDiskIndexByName(def, name);
>>>>> +    if (i < 0)
>>>>> +        return -1;
>>>>> +    virDomainDiskRemove(def, i);
>>>>> +    return 0;
>>>>> +}
>>>>> +
>>>>>  
>>>>>  int virDomainControllerInsert(virDomainDefPtr def,
>>>>>                                virDomainControllerDefPtr controller)
>>>>> diff --git a/src/conf/domain_conf.h b/src/conf/domain_conf.h
>>>>> index 30aeccc..320ca13 100644
>>>>> --- a/src/conf/domain_conf.h
>>>>> +++ b/src/conf/domain_conf.h
>>>>> @@ -1261,7 +1261,7 @@ int virDomainCpuSetParse(const char **str,
>>>>>                           int maxcpu);
>>>>>  char *virDomainCpuSetFormat(char *cpuset,
>>>>>                              int maxcpu);
>>>>> -
>>>>> +int virDomainDiskIndexByName(virDomainDefPtr def, const char *name);
>>>>>  int virDomainDiskInsert(virDomainDefPtr def,
>>>>>                          virDomainDiskDefPtr disk);
>>>>>  void virDomainDiskInsertPreAlloced(virDomainDefPtr def,
>>>>> @@ -1269,6 +1269,7 @@ void virDomainDiskInsertPreAlloced(virDomainDefPtr def,
>>>>>  int virDomainDiskDefAssignAddress(virCapsPtr caps, virDomainDiskDefPtr def);
>>>>>  
>>>>>  void virDomainDiskRemove(virDomainDefPtr def, size_t i);
>>>>> +int virDomainDiskRemoveByName(virDomainDefPtr def, const char *name);
>>>>>  
>>>>>  int virDomainControllerInsert(virDomainDefPtr def,
>>>>>                                virDomainControllerDefPtr controller);
>>>>> diff --git a/src/libvirt_private.syms b/src/libvirt_private.syms
>>>>> index c88d934..1761dfb 100644
>>>>> --- a/src/libvirt_private.syms
>>>>> +++ b/src/libvirt_private.syms
>>>>> @@ -243,11 +243,13 @@ virDomainDiskDefFree;
>>>>>  virDomainDiskDeviceTypeToString;
>>>>>  virDomainDiskErrorPolicyTypeFromString;
>>>>>  virDomainDiskErrorPolicyTypeToString;
>>>>> +virDomainDiskIndexByName;
>>>>>  virDomainDiskInsert;
>>>>>  virDomainDiskInsertPreAlloced;
>>>>>  virDomainDiskIoTypeFromString;
>>>>>  virDomainDiskIoTypeToString;
>>>>>  virDomainDiskRemove;
>>>>> +virDomainDiskRemoveByName;
>>>>>  virDomainDiskTypeFromString;
>>>>>  virDomainDiskTypeToString;
>>>>>  virDomainFSDefFree;
>>>>> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
>>>>> index dbd5bd3..d6d7ad0 100644
>>>>> --- a/src/qemu/qemu_driver.c
>>>>> +++ b/src/qemu/qemu_driver.c
>>>>> @@ -4137,8 +4137,27 @@ cleanup:
>>>>>  static int qemuDomainAttachDevicePersistent(virDomainDefPtr vmdef,
>>>>>                                              virDomainDeviceDefPtr newdev)
>>>>>  {
>>>>> +    virDomainDiskDefPtr disk;
>>>>>  
>>>>>      switch(newdev->type) {
>>>>> +    case VIR_DOMAIN_DEVICE_DISK:
>>>>> +        disk = newdev->data.disk;
>>>>> +        if (virDomainDiskIndexByName(vmdef, disk->dst) >= 0) {
>>>>> +            qemuReportError(VIR_ERR_INVALID_ARG,
>>>>> +                            _("target %s already exists."), disk->dst);
>>>>> +            return -1;
>>>>> +        }
>>>>> +        if (virDomainDiskInsert(vmdef, disk)) {
>>>>> +            virReportOOMError();
>>>>> +            return -1;
>>>>> +        }
>>>>> +        if (disk->bus == VIR_DOMAIN_DISK_BUS_VIRTIO) {
>>>>> +            if (qemuDomainAssignPCIAddresses(vmdef) < 0)
>>>>> +                return -1;
>>>>> +        } else if (virDomainDefAddImplicitControllers(vmdef) < 0)
>>>>> +            return -1;
>>>>
>>>> When qemuDomainAssignPCIAddresses() or virDomainDefAddImplicitControllers() failed,
>>>> we should remove disk from vmdef, otherwise, it will cause libvirtd crashed.
>>>>
>>>
>>> By returning -1, the vmdef is not saved and no one will see this modified
>>> vmdef (because the task is inactive here.)
>>>
>>> Do I need to care ?
>>
>> Yes, you need to care it.
>> By returning -1, the vmdef is not saved to disk. But vmdef is hashed, and we may access
>> it again before libvirtd is restarted.
>> When stoping libvirtd, we will free vmdef, this will cause disk is double freed.
>>
>> Here is the steps to reproduce this program:
>> # cat device.xml
>>     <disk type='file' device='disk'>
>>       <driver name='qemu' type='qcow2'/>
>>       <source file='/var/lib/libvirt/images/test3.img'/>
>>       <target dev='vdb' bus='virtio'/>
>>       <address type='pci' domain='0x0000' bus='0x00' slot='0x04' function='0x0'/>
>>     </disk>
>> # virsh attach-device vm1 device.xml --persistent
>> error: Failed to attach device from device.xml
>> error: An error occurred, but the cause is unknown
>>
>> Now, run attach-device again or stop libvirtd. It will cause libvirtd crashed.
>>
> Hmm, ok. what I should to unahs and free vmdef ?

No, we hash vmdef if it is persistent.
We should do some cleanup when qemuDomainAssignPCIAddresses() or
virDomainDefAddImplicitControllers() failed. For example, calling
virDomainDiskRemove() to remove it.

Another way to solve this problem is: we only malloc the memory and do not insert
the disk to vmdef before calling qemuDomainAssignPCIAddresses() or
virDomainDefAddImplicitControllers(), and insert it when this function successed.

> 
> 
> Thanks,
> -Kame
> 
> 


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