Xen devel - Jan 2005 - starting domain when block device already mounted

I just had a filesystem hosed in an unpriv domain (ext3 errors all over
the place), and then when I went to do a fsck on the block device it
told me it was already mounted, and sure enough, dom0 already had the
device mounted. Would that cause a filesystem crash, or at least errors?
Dom0 wasn''t doing anything to the filesystem, and the unpriv domain had
been up for a few weeks before this occurred.

Anyway, I''ve done this a few times before by mistake - made a few
changes to the unpriv domain''s filesystem from dom0 and forgot to
unmount it before starting the domain. Is there any easy way to get ''xm
create'' to check before starting that none of the block devices it is
about to export are in use? Such a thing would probably save me
countless headaches in the future! (or maybe it''s been done already?
I''m
running 2.0.1)

Thanks

James


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> I just had a filesystem hosed in an unpriv domain (ext3 
> errors all over
> the place), and then when I went to do a fsck on the block device it
> told me it was already mounted, and sure enough, dom0 already had the
> device mounted. Would that cause a filesystem crash, or at 
> least errors?
> Dom0 wasn''t doing anything to the filesystem, and the unpriv 
> domain had
> been up for a few weeks before this occurred.
Mounting an ext3 file system writeable in two domains is almost certain
to destroy it.

The tools try and prevent this. Was it a ''file:'' vbd?
There''s currently
no safety checks for those, but there should be for physical partition
and LVM volumes.

Ian
> Anyway, I''ve done this a few times before by mistake - made a few
> changes to the unpriv domain''s filesystem from dom0 and forgot to
> unmount it before starting the domain. Is there any easy way 
> to get ''xm
> create'' to check before starting that none of the block devices it
is
> about to export are in use? Such a thing would probably save me
> countless headaches in the future! (or maybe it''s been done 
> already? I''m
> running 2.0.1)
> 
> Thanks
> 
> James
> 
> 
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> https://lists.sourceforge.net/lists/listinfo/xen-devel
> 

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My disks line is:

disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]

The unpriv domain is up and running again, although I don''t know what
damage has been done. /etc/passwd was missing though which is not a good
sign. I found it in /lost+found, but who knows what else is missing!

Thanks

James
> -----Original Message-----
> From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
> Sent: Monday, 17 January 2005 09:34
> To: James Harper; xen-devel@lists.sourceforge.net
> Subject: RE: [Xen-devel] starting domain when block device already
mounted
> 
> > I just had a filesystem hosed in an unpriv domain (ext3
> > errors all over
> > the place), and then when I went to do a fsck on the block device it
> > told me it was already mounted, and sure enough, dom0 already had
the
> > device mounted. Would that cause a filesystem crash, or at
> > least errors?
> > Dom0 wasn''t doing anything to the filesystem, and the unpriv
> > domain had
> > been up for a few weeks before this occurred.
> 
> Mounting an ext3 file system writeable in two domains is almost
certain
> to destroy it.
> 
> The tools try and prevent this. Was it a ''file:'' vbd?
There''s
currently
> no safety checks for those, but there should be for physical partition
> and LVM volumes.
> 
> Ian
> 
> > Anyway, I''ve done this a few times before by mistake - made a
few
> > changes to the unpriv domain''s filesystem from dom0 and
forgot to
> > unmount it before starting the domain. Is there any easy way
> > to get ''xm
> > create'' to check before starting that none of the block
devices it
is
> > about to export are in use? Such a thing would probably save me
> > countless headaches in the future! (or maybe it''s been done
> > already? I''m
> > running 2.0.1)
> >
> > Thanks
> >
> > James
> >
> >
> > -------------------------------------------------------
> > The SF.Net email is sponsored by: Beat the post-holiday blues
> > Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek.
> > It''s fun and FREE -- well,
almost....http://www.thinkgeek.com/sfshirt
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/xen-devel
> >


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> My disks line is:
> 
> disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]
The double-mount protection might need tweaking to work with LVM volumes
- I doubt its been tested.

Could you add some debugging to check_mounted in xend/server/blkif.py ?

Thanks,
Ian


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Is it even present in 2.0.1? I can''t see any reference to check_mounted
in xend/server/blkif.py, or any .py files there.

Thanks

James
> -----Original Message-----
> From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
> Sent: Monday, 17 January 2005 10:01
> To: James Harper; xen-devel@lists.sourceforge.net
> Subject: RE: [Xen-devel] starting domain when block device already
mounted
> 
> > My disks line is:
> >
> > disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]
> 
> The double-mount protection might need tweaking to work with LVM
volumes
> - I doubt its been tested.
> 
> Could you add some debugging to check_mounted in xend/server/blkif.py
?
> 
> Thanks,
> Ian


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Are you mounting the device within dom0 after creating the domU?  I''m 
not sure there''s anything Xend can do about that.

Regards,

James Harper wrote:
>My disks line is:
>
>disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]
>
>The unpriv domain is up and running again, although I don''t know
what
>damage has been done. /etc/passwd was missing though which is not a good
>sign. I found it in /lost+found, but who knows what else is missing!
>
>Thanks
>
>James
>
>  
>
>>-----Original Message-----
>>From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
>>Sent: Monday, 17 January 2005 09:34
>>To: James Harper; xen-devel@lists.sourceforge.net
>>Subject: RE: [Xen-devel] starting domain when block device already
>>    
>>
>mounted
>  
>
>>>I just had a filesystem hosed in an unpriv domain (ext3
>>>errors all over
>>>the place), and then when I went to do a fsck on the block device it
>>>told me it was already mounted, and sure enough, dom0 already had
>>>      
>>>
>the
>  
>
>>>device mounted. Would that cause a filesystem crash, or at
>>>least errors?
>>>Dom0 wasn''t doing anything to the filesystem, and the
unpriv
>>>domain had
>>>been up for a few weeks before this occurred.
>>>      
>>>
>>Mounting an ext3 file system writeable in two domains is almost
>>    
>>
>certain
>  
>
>>to destroy it.
>>
>>The tools try and prevent this. Was it a ''file:'' vbd?
There''s
>>    
>>
>currently
>  
>
>>no safety checks for those, but there should be for physical partition
>>and LVM volumes.
>>
>>Ian
>>
>>    
>>
>>>Anyway, I''ve done this a few times before by mistake - made
a few
>>>changes to the unpriv domain''s filesystem from dom0 and
forgot to
>>>unmount it before starting the domain. Is there any easy way
>>>to get ''xm
>>>create'' to check before starting that none of the block
devices it
>>>      
>>>
>is
>  
>
>>>about to export are in use? Such a thing would probably save me
>>>countless headaches in the future! (or maybe it''s been done
>>>already? I''m
>>>running 2.0.1)
>>>
>>>Thanks
>>>
>>>James
>>>
>>>
>>>-------------------------------------------------------
>>>The SF.Net email is sponsored by: Beat the post-holiday blues
>>>Get a FREE limited edition SourceForge.net t-shirt from ThinkGeek.
>>>It''s fun and FREE -- well,
>>>      
>>>
>almost....http://www.thinkgeek.com/sfshirt
>  
>
>>>_______________________________________________
>>>Xen-devel mailing list
>>>Xen-devel@lists.sourceforge.net
>>>https://lists.sourceforge.net/lists/listinfo/xen-devel
>>>
>>>      
>>>
>
>
>
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>https://lists.sourceforge.net/lists/listinfo/xen-devel
>
>  
>


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Oops. This machine is actually using something pre-2.0, so please ignore
everything I''ve said :) I''ll complain again if it
doesn''t work when I
upgrade this machine.

Sorry about that.

James
> -----Original Message-----
> From: xen-devel-admin@lists.sourceforge.net [mailto:xen-devel-
> admin@lists.sourceforge.net] On Behalf Of James Harper
> Sent: Monday, 17 January 2005 09:49
> To: Ian Pratt; xen-devel@lists.sourceforge.net
> Subject: RE: [Xen-devel] starting domain when block device already
mounted
> 
> My disks line is:
> 
> disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]
> 
> The unpriv domain is up and running again, although I don''t know
what
> damage has been done. /etc/passwd was missing though which is not a
good
> sign. I found it in /lost+found, but who knows what else is missing!
> 
> Thanks
> 
> James
> 
> > -----Original Message-----
> > From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
> > Sent: Monday, 17 January 2005 09:34
> > To: James Harper; xen-devel@lists.sourceforge.net
> > Subject: RE: [Xen-devel] starting domain when block device already
> mounted
> >
> > > I just had a filesystem hosed in an unpriv domain (ext3
> > > errors all over
> > > the place), and then when I went to do a fsck on the block device
it
> > > told me it was already mounted, and sure enough, dom0 already had
> the
> > > device mounted. Would that cause a filesystem crash, or at
> > > least errors?
> > > Dom0 wasn''t doing anything to the filesystem, and the
unpriv
> > > domain had
> > > been up for a few weeks before this occurred.
> >
> > Mounting an ext3 file system writeable in two domains is almost
> certain
> > to destroy it.
> >
> > The tools try and prevent this. Was it a ''file:''
vbd? There''s
> currently
> > no safety checks for those, but there should be for physical
partition
> > and LVM volumes.
> >
> > Ian
> >
> > > Anyway, I''ve done this a few times before by mistake -
made a few
> > > changes to the unpriv domain''s filesystem from dom0 and
forgot to
> > > unmount it before starting the domain. Is there any easy way
> > > to get ''xm
> > > create'' to check before starting that none of the block
devices it
> is
> > > about to export are in use? Such a thing would probably save me
> > > countless headaches in the future! (or maybe it''s been
done
> > > already? I''m
> > > running 2.0.1)
> > >
> > > Thanks
> > >
> > > James
> > >
> > >
> > > -------------------------------------------------------
> > > The SF.Net email is sponsored by: Beat the post-holiday blues
> > > Get a FREE limited edition SourceForge.net t-shirt from
ThinkGeek.
> > > It''s fun and FREE -- well,
> almost....http://www.thinkgeek.com/sfshirt
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/xen-devel
> > >
> 
> 
> 
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> Are you mounting the device within dom0 after creating the domU? 
I''m
> not sure there''s anything Xend can do about that.
Yes that''s correct - if you try and mount domain filesystems read /
write
after the domain is started then it''ll probably succeed but the
filesystem
will get hosed.

Even mounting read-only in dom0 will confuse the filesystem driver if the 
domain writes anything.

Cheers,
Mark
> Regards,
>
> James Harper wrote:
> >My disks line is:
> >
> >disk = [ ''phy:vg00/mail,0301,w'',
''phy:vg00/mail-swap,0302,w'' ]
> >
> >The unpriv domain is up and running again, although I don''t
know what
> >damage has been done. /etc/passwd was missing though which is not a
good
> >sign. I found it in /lost+found, but who knows what else is missing!
> >
> >Thanks
> >
> >James
> >
> >>-----Original Message-----
> >>From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
> >>Sent: Monday, 17 January 2005 09:34
> >>To: James Harper; xen-devel@lists.sourceforge.net
> >>Subject: RE: [Xen-devel] starting domain when block device already
> >
> >mounted
> >
> >>>I just had a filesystem hosed in an unpriv domain (ext3
> >>>errors all over
> >>>the place), and then when I went to do a fsck on the block
device it
> >>>told me it was already mounted, and sure enough, dom0 already
had
> >
> >the
> >
> >>>device mounted. Would that cause a filesystem crash, or at
> >>>least errors?
> >>>Dom0 wasn''t doing anything to the filesystem, and the
unpriv
> >>>domain had
> >>>been up for a few weeks before this occurred.
> >>
> >>Mounting an ext3 file system writeable in two domains is almost
> >
> >certain
> >
> >>to destroy it.
> >>
> >>The tools try and prevent this. Was it a ''file:''
vbd? There''s
> >
> >currently
> >
> >>no safety checks for those, but there should be for physical
partition
> >>and LVM volumes.
> >>
> >>Ian
> >>
> >>>Anyway, I''ve done this a few times before by mistake -
made a few
> >>>changes to the unpriv domain''s filesystem from dom0
and forgot to
> >>>unmount it before starting the domain. Is there any easy way
> >>>to get ''xm
> >>>create'' to check before starting that none of the
block devices it
> >
> >is
> >
> >>>about to export are in use? Such a thing would probably save me
> >>>countless headaches in the future! (or maybe it''s been
done
> >>>already? I''m
> >>>running 2.0.1)
> >>>
> >>>Thanks
> >>>
> >>>James
> >>>
> >>>
> >>>-------------------------------------------------------
> >>>The SF.Net email is sponsored by: Beat the post-holiday blues
> >>>Get a FREE limited edition SourceForge.net t-shirt from
ThinkGeek.
> >>>It''s fun and FREE -- well,
> >
> >almost....http://www.thinkgeek.com/sfshirt
> >
> >>>_______________________________________________
> >>>Xen-devel mailing list
> >>>Xen-devel@lists.sourceforge.net
> >>>https://lists.sourceforge.net/lists/listinfo/xen-devel
> >
> >-------------------------------------------------------
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>
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