Xen users - Dec 2006 - Re: RE: RE: Why creating DomU failed (seems it is duetoLVM)

Hi, Mats,

And more info:
After I modified init script in DomU''s initrd, it can boot
successfully.
it is that i modified:
	mount -o defaults --ro -t ext3 /dev/root /sysroot
to 
	mount -o defaults --ro -t ext3 /dev/sda1 /sysroot
it seems DomU loader just can''t find out which is the root device.

I don''t know why it works, so I checked the mails before, and still
can''t know why...

Best,
Binbin 

======= 2006-12-13 20:40:29 you wrote:======
>> -----Original Message-----
>> From: Zhang Binbin [mailto:binbinzh@126.com] 
>> Sent: 13 December 2006 12:22
>> To: Petersson, Mats
>> Subject: Re: RE: [Xen-users] Why creating DomU failed (seems 
>> it is due toLVM)
>> 
>> I can''t understand using the same kernel(i.e. 2.6.16-xen), 
>> why Dom0 boots up smoothly, but DomU can''t, if it is a driver 
>> missing problem.
>
>No, and I don''t think that''s the post I was actually
commenting on.
>Since you seem to have snipped the original post I was commenting on,
>the original context I was commenting on isn''t in this post... 
>
>That sounds like some other problem - particularly since DomU
doesn''t
>actually touch any of the hardware directly (unless you specifically add
>pci_hide to Dom0 and assign the device using pci = ... In the
>configuration of DomU). 
>
>If your initrd is the same as that of Dom0, then it wouldn''t have
the
>frontend drivers that the para-virtual device is required to use (unless
>you''re using a HVM domain, in which case you shouldn''t
just copy the
>original Xen installation, but use a standard non-xen kernel for the
>DomU). 
>
>Note that initrd should contain the drivers necessary to boot the
>system, and that''s different for Dom0 and DomU, since DomU uses the
>para-virtual frontend/backend driver pair (where the backend driver is
>in Dom0 and translates the request from DomU into a reasonable system
>request for Dom0 to perform the right operation on the "device"
that
>DomU uses). 
>
>--
>Mats
>
>
>> 
>> Thanks. 
>> 
>> >Creating an initrd file isn''t rocket surgery in itself
>> >
>> >Making a system boot when you haven''t got the right
drivers can be a
>> >pain in the posterior... 
>> >
>> >If you know what drivers you need to make the system boot and
you''re
>> >changing your config file to make that work, you may just as 
>> well skip
>> >the part of making something a module - it doesn''t
ACTUALLY help
>> >anything to have a module instead of a built-in driver. 
>> >
>> >On the other hand, if you don''t have a clue what driver
you actually
>> >need, and you''re adding drivers "wholesale", you
probably
>> don''t want to
>> >bloat the kernel by adding all of your drivers as
"builtin",
>> even if it
>> >saves you a bit of hassle by not creating an initrd. 
>> >
>> >It''s often a good idea to start by using a simple setup -
LVM, RAID,
>> >SCSI all add extra complications and more drivers are needed. Some
of
>> >which may not work in a particular permutation of Xen + Dom0! If
you
>> >can''t make the machine boot in a complex setup, you may
want to try a
>> >simpler setup before you try reconfiguring the kernel. 
>> Obviously, if you
>> >use LVM, you''ll need the relevant "lvm modules"
either builtin (my
>> >recommendation) or as a module when you build the initrd. 
>> >
>> >Carefull inspection of "dmesg" and any other "boot
output"
>> will also be
>> >useful. "lspci" is a good hint. 
>> >
>> >Note also that if you build Xen on one machine, and install 
>> on another,
>> >you''ll need to do "depmod" as well as
"mkinitrd" - and if
>> you''re copying
>> >individual files, make sure you copy the modules to the right place
>> >under /lib/modules/ - it happens automagically if you copy the
whole
>> >.../dist directory, but I sometimes try to cheat by copying 
>> individual
>> >files, and it''s been known to "fail". 
>> >
>> >--
>> >Mats
>> >> 
>> >> -- 
>> >> Steven
>> >> 
>> >> 
>> >> _______________________________________________
>> >> Xen-users mailing list
>> >> Xen-users@lists.xensource.com
>> >> http://lists.xensource.com/xen-users
>> >> 
>> >> 
>> >> 
>> >
>> >
>> >
>> >_______________________________________________
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>> >http://lists.xensource.com/xen-users
>> 
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>> 
>> 
>> 
>> 
>> 
>> 
>> 
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> -----Original Message-----
> From: Zhang Binbin [mailto:binbinzh@126.com] 
> Sent: 13 December 2006 13:06
> To: Petersson, Mats
> Cc: xen-users
> Subject: Re: RE: RE: [Xen-users] Why creating DomU failed 
> (seems it is duetoLVM)
> 
> Hi, Mats,
> 
> And more info:
> After I modified init script in DomU''s initrd, it can boot 
> successfully.
> it is that i modified:
> 	mount -o defaults --ro -t ext3 /dev/root /sysroot
> to 
> 	mount -o defaults --ro -t ext3 /dev/sda1 /sysroot
> it seems DomU loader just can''t find out which is the root device.
> 
> I don''t know why it works, so I checked the mails before, and 
> still can''t know why...
Ah, ok, sorry, missed the connection there. 

That makes sense. /dev/root is a "symbolic link", which probably
doesn''t
exist in your /dev on the DomU "disk"... You may be able to achieve
the
same thing by "ln -s /dev/sda1 /dev/root" before the mount command. (I
never get the arguments for ln right, so they are probably supposed to
go the other way around!)

--
Mats
 



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Thanks.
Then it is likely that DomU loader have no idea which is the root device.
I suppose there may be something missing when DomU creator parse DomU config and
create vbd.
DomU config file do give enough info about the root device.
But why I never encountered this problem before (I have smoothly installed
Xen-2.0 with redhat-***, Xen-3.0 with redhat-***, fedora-***, centos-4.), except
when I played it with CentOS-4.4-x86_64 and Fedora on new bought machines this
time.
Still don''t understand.

My solution isn''t a good idea. It will require different initrd for
DomU with a different root device...


======= 2006-12-13 21:36:27 you wrote:======
>> -----Original Message-----
>> From: Zhang Binbin [mailto:binbinzh@126.com] 
>> Sent: 13 December 2006 13:06
>> To: Petersson, Mats
>> Cc: xen-users
>> Subject: Re: RE: RE: [Xen-users] Why creating DomU failed 
>> (seems it is duetoLVM)
>> 
>> Hi, Mats,
>> 
>> And more info:
>> After I modified init script in DomU''s initrd, it can boot 
>> successfully.
>> it is that i modified:
>> 	mount -o defaults --ro -t ext3 /dev/root /sysroot
>> to 
>> 	mount -o defaults --ro -t ext3 /dev/sda1 /sysroot
>> it seems DomU loader just can''t find out which is the root
device.
>> 
>> I don''t know why it works, so I checked the mails before, and 
>> still can''t know why...
>
>Ah, ok, sorry, missed the connection there. 
>
>That makes sense. /dev/root is a "symbolic link", which probably
doesn''t
>exist in your /dev on the DomU "disk"... You may be able to
achieve the
>same thing by "ln -s /dev/sda1 /dev/root" before the mount
command. (I
>never get the arguments for ln right, so they are probably supposed to
>go the other way around!)
>
>--
>Mats
> 
>
>
>
>_______________________________________________
>Xen-users mailing list
>Xen-users@lists.xensource.com
>http://lists.xensource.com/xen-users
= = = = = = = = = = = = = = = = = = = 			





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