[CentOS-virt] xen device mapping/translation

Andy Grimm agrimm at gmail.com
Wed Jan 16 16:06:47 UTC 2013 

On Wed, Jan 16, 2013 at 10:04 AM, Luis Fernando Alen
<luis.alen at izap.com.br>wrote:

> Andy,
>
> Actually I'm not trying to build a whole new kernel. I'm just trying to
> apply the patched module into my actual kernel.
>
> Does this patch really requires a kernel rebuild, or you mean building a
> new one will save me from the trouble of applying the module into the
> running kernel?
>

Perhaps I'm missing some key information here, but you should not need to
rebuild anything at all.  You only need to modify the ramdisk to load the
xen_blkfront module with sda_is_xvda=1 .   There are various ways to do
this; adding xen_blkfront.sda_is_xvda=1 to the kernel command line in
grub.conf is probably the most expedient.

Hope this helps.

Andy



>
> Luis Alen
> www.izap.com.br
> Ligue com tarifa local de todo o Brasil 4020.3000
>
>
>
> On Wed, Jan 16, 2013 at 10:57 AM, Nico Kadel-Garcia <nkadel at gmail.com>wrote:
>
>>
>>
>> On Tue, Jan 15, 2013 at 8:39 PM, Luis Fernando Alen <
>> luis.alen at izap.com.br> wrote:
>>
>>> Thank you, Andy.
>>>
>>> I tried to apply the patch you guys mentioned by compiling the module
>>> following instructions at
>>> http://wiki.centos.org/HowTos/BuildingKernelModules#head-d2e4c05886f94c701e4ae74387d41d8c40c25d01,
>>> but it didn't work.
>>>
>>> I've been struggling with it for the last 8 hours and no luck so far.
>>>
>>> I really don't know what's wrong. I'm not a linux kernel developer and
>>> I'm most likely failing because of something stupid.
>>>
>>> I know this must not the right place to ask for help on such matters,
>>> but if you guys could shed some light here, I'd really appreciate that.
>>>
>>> Well, if you're up to it, here's the situation:
>>>
>>> Looks like the module compilation worked (no errors or warnings occurred
>>> when I followed the instructions at the centos wiki), but I'm unable to
>>> load the new module to my running kernel.
>>>
>>
>> If you're building a new kernel, you should really give it a new name and
>> fully install it as a distinct kernel. The safest way to do this is to work
>> from the SRPM, put the patch in *there* and  update the "Release:"
>> number in the kenrel.spec file This will avoid precisely the issues you
>> described.
>>
>> Do you need a walkt hrough on rebuilding a package from SRPM's?
>>
>>
>>> I even copied the compiled and patched module to
>>> /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/ (overwrote
>>> the original) and /lib/modules/2.6.32-279.19.1.el6.x86_64/extra and
>>> rebooted the instance...
>>>
>>> Also, dmesg does not complain about a thing...
>>>
>>> *# modinfo
>>> /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/xen-blkfront.ko
>>> *
>>> *filename:
>>> /lib/modules/2.6.32-279.19.1.el6.x86_64/kernel/drivers/block/xen-blkfront.ko
>>> *
>>> *alias:          xenblk*
>>> *alias:          xen:vbd*
>>> *alias:          block-major-202-**
>>> *license:        GPL*
>>> *description:    Xen virtual block device frontend*
>>> *srcversion:     B00B4183E470515A96DA320*
>>> *depends:        *
>>> *vermagic:       2.6.32-279.19.1.el6.x86_64 SMP mod_unload modversions *
>>> *parm:           sda_is_xvda:sdX in guest config translates to xvdX,
>>> not xvd(X+4) (bool)*
>>> *
>>> *
>>> *# uname -r*
>>> *2.6.32-279.19.1.el6.x86_64*
>>>
>>> I also tried to remove the module and insert the patched one with
>>> insmod, but modprobe and rmmod are unable to unload it. They say it's in
>>> use.
>>>
>>> *# lsmod |grep blkfront*
>>> *xen_blkfront           15495  1 *
>>>
>>> I don't know what this "1" stands for, but if I were to guess, I'd say
>>> it's something unremovable...
>>>
>>> Please let me know if you need any other information.
>>>
>>> Thanks,
>>>
>>>
>>>
>>>
>>>
>>> Luis Alen
>>> www.izap.com.br
>>> Ligue com tarifa local de todo o Brasil 4020.3000
>>>
>>>
>>>
>>> On Tue, Jan 15, 2013 at 4:13 PM, Andy Grimm <agrimm at gmail.com> wrote:
>>>
>>>> See https://bugzilla.redhat.com/show_bug.cgi?id=729586
>>>>
>>>> On Tue, Jan 15, 2013 at 1:10 PM, Luis Fernando Alen <
>>>> luis.alen at izap.com.br> wrote:
>>>>
>>>>> Hello, list.
>>>>>
>>>>> Yesterday I was pleased to see that Centos has released official
>>>>> images at the aws marketplace. Nice job.
>>>>>
>>>>> Today I started playing with the Centos 6.3 image (
>>>>> https://aws.amazon.com/marketplace/pp/B00A6L6F9I, on which I plan to
>>>>> deploy a gluster cluster in production soon) and noticed a weird thing.
>>>>>
>>>>> EBS Volumes attached to sd<X> are translated to xvd<Y> at the OS
>>>>> level. However, after a few research and IRC chat, I figured out that it's
>>>>> not weird, it's actually a normal and expected behavior (thanks for your
>>>>> help, z00dax).
>>>>>
>>>>> sdX is actually mapped to xvdX+4. There is a consistent offset of 4.
>>>>> Suppose you attach an ebs volume to /dev/sdf. It'll be translated to xvdj
>>>>> at the OS level. sdg to xvdk, sdh to xvdl and so on.
>>>>>
>>>>> Allright. After having figured the mystery out, it became easy to work
>>>>> on automations that deal with ebs volumes and file systems, such as volumes
>>>>> created, attached and mounted on the fly, snapshots that freeze file
>>>>> systems and so on...
>>>>>
>>>>> However, I really do think to myself: Wouldn't it be cleaner if the
>>>>> image use simple translation (sdX to xvdX)? If I'm not wrong, Rightscale
>>>>> uses this on their Centos images and it's much simpler. There's no extra
>>>>> work needed to deal with that 4 offset when you want to automate things.
>>>>>
>>>>> Is there a reasonable reason for the 4 offset which makes it
>>>>> unchangeable?
>>>>>
>>>>> It's just a thought. I think it's worth considering it..
>>>>>
>>>>> Luis Alen
>>>>> www.izap.com.br
>>>>> Ligue com tarifa local de todo o Brasil 4020.3000
>>>>>
>>>>>
>>>>> _______________________________________________
>>>>> CentOS-virt mailing list
>>>>> CentOS-virt at centos.org
>>>>> http://lists.centos.org/mailman/listinfo/centos-virt
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> CentOS-virt mailing list
>>>> CentOS-virt at centos.org
>>>> http://lists.centos.org/mailman/listinfo/centos-virt
>>>>
>>>>
>>>
>>> _______________________________________________
>>> CentOS-virt mailing list
>>> CentOS-virt at centos.org
>>> http://lists.centos.org/mailman/listinfo/centos-virt
>>>
>>>
>>
>> _______________________________________________
>> CentOS-virt mailing list
>> CentOS-virt at centos.org
>> http://lists.centos.org/mailman/listinfo/centos-virt
>>
>>
>
> _______________________________________________
> CentOS-virt mailing list
> CentOS-virt at centos.org
> http://lists.centos.org/mailman/listinfo/centos-virt
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.centos.org/pipermail/centos-virt/attachments/20130116/68e86b63/attachment.html

More information about the CentOS-virt mailing list