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[Qemu-devel] Re: [PATCH] Snapshot block device support

From: Fabrice Bellard
Subject: [Qemu-devel] Re: [PATCH] Snapshot block device support
Date: Fri, 04 Jul 2003 16:51:25 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:0.9.9) Gecko/20020408

Rusty Russell wrote:
> In message <address@hidden> you write:
>> I had plans to implement "copy on write" disk images...I find your
>>  approach original. My initial plan was just to add a second disk
>> image for each disk containing the changes. It should be easy to
>> do it from your code (for example by adding options '-hdacow file'
>> where file is the snapshot file you use).
> Sure: I used a temporary (unlinked) file because I couldn't see much
> point in keeping it around.  Since most filesystems do sparse files,
> it's quite efficient, too.
> -hdacow with an optional argument would work really well, if that's desired
> behaviour.
> I'm glad I finally beat you to implementing something: you're
> usually too quick 8)

Well, I don't have to maintain parts of the Linux kernel at the same time :-)

I am going to modify your patch today so that -hdacow is supported.

>> About IDE, it is working (at least with kernel 2.4.20). Someone
>> has even compiled a linux kernel inside QEMU (slowdown factor of
>> about 15), so vl begins to be usable for real tasks. There are
>> still known problems if several processes use floating point at
>> the same time.
> OK, I'm getting errors with IDE on 2.5, but shouldn't be too hard to
> track down.

I tested with 2.5.74 and fixed the initial IDE error. I also added the
emulation of the PC 'reset' pin so that vl can be shut down as a normal Linux system (only hard reset is supported, not power off, as it would require a more complicated real mode APM bios emulation).

Now I am looking for potential original uses of vl/QEMU !


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