[libvirt] Consultation of the patch "util: Prepare helpers for unpriv_sgio setting"

Osier Yang jyang at redhat.com
Wed Mar 13 07:38:42 UTC 2013


On 2013年03月13日 15:20, yuxh wrote:
> On 03/13/2013 11:33 AM, Osier Yang wrote:
>> On 2013年03月13日 11:04, yuxh wrote:
>>> To Osier Yang
>>>
>>> Sorry for disturbing you on the working time, but I really need your
>>> help.
>>> I met a problem when I do the virtualization test on the environment of
>>> (Host: RHEL6.4GA. Guest: RHEL6.4GA) and it seems to have relationship
>>> with your patch of "util: Prepare helpers for unpriv_sgio setting".
>>
>> Never mind, it's the bug I produced. :(
>>
>>>
>>> I added a disk to virtio-scsi bus through the VM's XML file like this:
>>> <disk type='block' device='disk'>
>>> <driver name='qemu' type='raw' io='threads'/>
>>> <source dev='/mnt/test.raw'/>
>>> <target dev='sdb' bus='scsi'/>
>>> <shareable/>
>>> </disk>
>>>
>>> Then when I started the VM, I met the error.
>>> [root at build SOURCES]# virsh start pan64ga
>>> error: Failed to start domain pan64ga
>>> error: Unable to get minor number of device '/mnt/test.raw': Invalid
>>> argument
>>>
>>> [root at build SOURCES]#
>>>
>>> I tried other source files and other way of using if and I found:
>>> 1). If we use the files which format is raw, qed and qcow2 as the disk
>>> this error occur again.
>>> 2). If we use partition(such as /dev/sdb1) or whole disk(such as
>>> /dev/sdb) this error doesn't occur.
>>> 3). If we delete the "<shareable/>" then files, partition and disk all
>>> can be used correctly.
>>>
>>> And I investigate the error msg. it is returned by qemuGetSharedDiskKey
>>> fuction.
>>> char *
>>> qemuGetSharedDiskKey(const char *disk_path)
>>> {
>>> ...
>>> // error occur here. return value is -22
>>> if ((rc = virGetDeviceID(disk_path, &maj, &min)) < 0) {
>>> virReportSystemError(-rc,
>>> _("Unable to get minor number of device '%s'"),
>>> disk_path);
>>> return NULL;
>>> }
>>> ...
>>> }
>>>
>>> Go on the virGetDeviceID fuction:
>>> int
>>> virGetDeviceID(const char *path, int *maj, int *min)
>>> {
>>> ...
>>>
>>> if (!S_ISBLK(sb.st_mode)) {
>>> VIR_FREE(canonical_path);
>>> return -EINVAL; // error occur here and it return -22
>>> }
>>> ...
>>> }
>>>
>>> So the error occur place is "S_ISBLK(sb.st_mode)" and I tried compiled
>>> the libvirt with these lines deleted and the error didn't happen again.
>>> Also I checked the disk if VM and it worked well.
>>> I found this fuction virGetDeviceID is come from your patch of "util:
>>> Prepare helpers for unpriv_sgio setting". But I am not familiar with
>>> libvirt.
>>> So I have to consult with you about whether this "S_ISBLK" check is
>>> vital and If we can delete it or
>>> find out some method to avoid this error so we can use the file as
>>> shared disk in VM.
>>
>> It's fixd by
>> https://www.redhat.com/archives/libvir-list/2013-February/msg01024.html,
>> which is already committed to upstream, and backported
>> to 6.4.z. You will see the fix in the new build, which will come soon.
>>
>> Regards,
>> Osier
> Sorry, I have tried the the libvirt's upstream code and it still have
> this error.
> According to the code, if we use "<disk type='block' device='disk'> "
> and "<shareable/> " to set the disk's configuration in VM's XML file, it
> will go through like below:
>
> int
> qemuAddSharedDisk(virQEMUDriverPtr driver,
> virDomainDiskDefPtr disk,
> const char *name)
> { ...
> if (!(key = qemuGetSharedDiskKey(disk->src)))
> goto cleanup;
> ...
> }
>
> char *
> qemuGetSharedDiskKey(const char *disk_path)
> {
> ...
> if ((rc = virGetDeviceID(disk_path, &maj, &min)) < 0) {
> virReportSystemError(-rc,
> _("Unable to get minor number of device '%s'"),
> disk_path);
> return NULL;
> }
> ...
> }
>
> int
> virGetDeviceID(const char *path, int *maj, int *min)
> {
> struct stat sb;
>
> if (stat(path, &sb) < 0)
> return -errno;
>
> if (!S_ISBLK(sb.st_mode))
> return -EINVAL;
>
> if (maj)
> *maj = major(sb.st_rdev);
> if (min)
> *min = minor(sb.st_rdev);
>
> return 0;
> }
>
> To make a long story short, the virGetDeviceID fuction want to get the
> maj and min number of the source file which we provided as the VM's
> disk. But the file such as /mnt/test.raw doesn't have the maj and min
> number.
> So virGetDeviceID return " -EINVAL" and qemuGetSharedDiskKey print the
> error message of "Unable to get minor number of device /mnt/test.raw".
> That's the reason the VM can't be started.
> So I just want to know now, if the way I used a file to act as VM's disk
> and set "<disk type='block' device='disk'>" , "<shareable/> " at the
> same time is reasonable.

Hum, sorry I didn't read your problem carefully. But...

It's not reasonable. As the disk source you use is /mnt/test.raw, I
believe it's not a block device. However, you used disk type='block'.
Libvirt honors what you specified, and tries to grab the device IDs
of the disk source (it expects the disk source is block, but it's not).

Regards,
Osier




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