Re: [uml-user] Cannot move COW backing file

[Blaisorblade <bla...@ya...>]

On Saturday 24 September 2005 20:12, mj...@es... wrote:
> Hi,

> I cannot successfully move the backing file of a COW file. I am
> following the instructions for moving the backing file given at:

> http://user-mode-linux.sourceforge.net/shared_fs.html
>
> e.g. I had
> /somewhere/root_fs
> /somewhere/root_fs_cow
>
> starting um with:
> ./linux ubd0=/somewhere/root_fs_cow,/somewhere/root_fs
> all works fine
>
> Now move the root_fs
> mv /somewhere/root_fs /new/root_fs
>
> now start um:
> ./linux ubd0=/somewhere/root_fs_cow,/new/root_fs
> ....

> Couldn't stat '/somewhere/root_fs', err = 2
> Couldn't stat "/somewhere/root_fs" : err = 2
This is what you complain about, but
> Failed to get modification time of backing file "/somewhere/root_fs", err =
> 2

> Failed to open '/somewhere/root_fs_cow', errno = 2 
What's this? It doesn't even find the COW file. Would you please double check 
your configuration (say a startup script broken by the move or anyway some 
other change)?

> VFS: Cannot open root device "98:0" or unknown-block(98,0)
> Please append a correct "root=" boot option
> Kernel panic - not syncing: VFS: Unable to mount root fs on
> unknown-block(98,0)

> I checked that the root_fs system was not corrupted by reverting to
> the original location
> cp -a /new/root_fs /somewhere/root_fs

> Now it works again using the first um invocation showing that the move
> itself was not a problem.

> The documentation implies that starting um with the new backing file
> location updates the original COW file:
>
> "UML will notice the mismatch between the command line and COW header,
> check the size and mtime of the new backing file path, and update the
> COW header to reflect it if it checks out."
>
> Can anyone report if this actually works:
>
> I am using a gentoo 2005.1 system with:
> 2.6.12-gentoo-r6-skas3-v8.2 host kernel
> UM kernel is the same source tree (gentoo patched 2.6.12)
Btw:
> usermode-utilities-20040406
Hope that's the -r1 Gentoo release (which contains a local DoS security fix - 
an unprivileged user could easily bring down an interface).
-- 
Inform me of my mistakes, so I can keep imitating Homer Simpson's "Doh!".
Paolo Giarrusso, aka Blaisorblade (Skype ID "PaoloGiarrusso", ICQ 215621894)
http://www.user-mode-linux.org/~blaisorblade

	

	
		
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