Re: [Xen-users] forcing disk in read only also if mounted

[Javier Guerra <javier@xxxxxxxxxxx>]

On Monday 15 January 2007 1:19 pm, Daniele Palumbo wrote:
> it is a "known issue" of my hosts.
>
> let's make a short example:
> if(i need new modules) then i have a new kernel && i have rebooted in a
> short time
> else i know that i have to reboot my domu to gain last modules.

first thing; as you know this isn't supported by any non-network non-cluster 
filesystem.

what you could do is not mount in Dom0 at all; then all DomUs would work 
read-only using regular 'r' flag.  then, to update it you shoud:

1) unmount from all DomUs
2) mount rw in Dom0
3) modify at will
4) umount from Dom0
5) mount on all DomUs (still ro)

but, you could also:  (**DANGEROUS**)
1) keep mounted ro in all DomUs
2) mount rw in Dom0
--- as soon as you do that, all DomUs are unstable!!  ---
3) modify in Dom0  (pray that DomUs don't crash!)
4) umount from Dom0
5) remount on all DomUs (still ro)

the point is that the 'r', 'w' or 'w!' flag is only checked at DomU creation 
time; if at that moment the block device isn't mounted rw by anybody 
(including Dom0), it will work.  later, you could mount it behind Xen's back 
(and risk all Dom0s, of course)

-- 
Javier

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