[uml-devel] mounting COW on HOST?

[uml-devel] mounting COW on HOST?

[roland]

hi!
one thing came to my mind today: why not porting the COW feature of UML to 
the "mainstream" linuxkernel itself?
i would find this useful - not only in relation to UML.
maybe there is already something like this? don`t know....
what would we need? modifying loopdevice(mount -o loop...) code? perhaps using 
lufs for that? (btw: long awaited read/write support for ntfs partitions has 
been implemented via lufs and native windows ntfs.sys driver!) 
maybe this has been discussed already?

regards
roland



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Re: [uml-devel] mounting COW on HOST?

[greg]

Roland,

It wouldn't be that tough to write a COW block device for the standard
kernel.  In fact, if we did that, we could get rid of the COW hack in
the ubd device.  

The basic idea of COW is a bitmap to represent all the sectors of the
block device, a backing block device and a cow block device.  Any
blocking device should work.  

I have also thought of changing the index to be a 4 byte offset, this
would useful for live CD distros with a floppy device.  The floppy
device becomes the COW disk while the backing file is the CDROM.  I
haven't done the math on the usability of 1.4MB floppy or the recovery
mechanism in case of a kernel panic, etc...  But having a live CD in
which any sector could be changed might be interesting, at least make it
easier for the live CD people.

See ya,
Greg

On Mon, 2003-12-08 at 17:45, roland wrote:
> hi!
> one thing came to my mind today: why not porting the COW feature of UML to 
> the "mainstream" linuxkernel itself?
> i would find this useful - not only in relation to UML.
> maybe there is already something like this? don`t know....
> what would we need? modifying loopdevice(mount -o loop...) code? perhaps using 
> lufs for that? (btw: long awaited read/write support for ntfs partitions has 
> been implemented via lufs and native windows ntfs.sys driver!) 
> maybe this has been discussed already?
> 
> regards
> roland
> 
> 
> 
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Re: [uml-devel] mounting COW on HOST?

[Russell Coker]

On Tue, 9 Dec 2003 13:10, greg <greg@lonnon.org> wrote:
> It wouldn't be that tough to write a COW block device for the standard
> kernel.  In fact, if we did that, we could get rid of the COW hack in
> the ubd device.

Isn't this already done via LVM snapshots?

-- 
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Re: [uml-devel] mounting COW on HOST?

[Matt Zimmerman]

On Tue, Dec 09, 2003 at 01:45:59AM +0100, roland wrote:

> one thing came to my mind today: why not porting the COW feature of UML to 
> the "mainstream" linuxkernel itself?
> i would find this useful - not only in relation to UML.
> maybe there is already something like this? don`t know....
> what would we need? modifying loopdevice(mount -o loop...) code? perhaps using 
> lufs for that? (btw: long awaited read/write support for ntfs partitions has 
> been implemented via lufs and native windows ntfs.sys driver!) 
> maybe this has been discussed already?

This has come up several times before; search the mailing list archives.

-- 
 - mdz


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