Re: [Xen-users] Share of disks in read only between dom0 and domU.

[Michel Gaudet <Michel.Gaudet@xxxxxxxx>]

Goswin von Brederlow a écrit :
> Michel Gaudet <Michel.Gaudet@xxxxxxxx> writes:
>
> > Hello !
> >
> > Because of a special config of my grub boot system, i try to export in
> > a domU, in read only mode, one of my disk partition mounted in the
> > dom0 (in RW)  and i don't succeed because xen refuse to export this
> > disk partition in a domU.
> >
> > extract of the conf :
> >
> > disk = [ 'phy:/dev/sda,ioemu:hda,r' , 'phy:/dev/sda6,ioemu:sda6,r]' ,
> > 'phy:/dev/sda1,ioemu:sda1' ]
> >
> > The first disk for grub to access the MBR , the second for grub to obtain its 
> > 1.5 and
> > second stage and the third to reach the guest OS.
> >
> > I block at the export of the sda6 which is the / of my dom0 with the message :
> >
> > Error: Device 2054 (vbd) could not be connected.
> > Device /dev/sda6 is mounted read-write in the privileged domain,
> > and so cannot be mounted read-only by a guest.
> And it has good reason to refuse this.
And as i say belox i understand this.

> > If i don't mount the /dev/sda6 the domU begin the boot but it freeze with the 
> > error :
> >
> > Booting from Hard Disk
> > GRUB Loading stage1.5.
> >
> > GRUB loading, please wait...
> > Error 5
> >
> > Error 5 is : Partition table invalid or corrupt
> >
> > But we can boot normally our 2 OS without xen.
> You need sda there, not sda6. There is no partition table on sda6.
Yes the partition is on /dev/sda which is mounted also; but grub stage 1.5 and 2 are on 
/dev/sda6 and grub access its stage > 1 thru the file system onto it is installed then i 
think i do mount /dev/sda6 which contain the grub stage > 1.
> > I think it is because it don't see the partition onto which is the grub install 
> > : /dev/sda6
> >
> > I understand why it is forbidden to mount in RW the same disk but in R ?
> Because the filesystem structures will be in some inconsistent state
> and change underneath the caches the domU maintains without
> notice. You quickly get a mix of old and new data.
>
> For grub this might not matter as it is so low level but xen doesn't
> know you only want to start grub there.
>
> MfG
>         Goswin
Thanks.


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