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Re: [Qemu-devel] Making qemu images executable (and store command line a

From: Ben Taylor
Subject: Re: [Qemu-devel] Making qemu images executable (and store command line arguments in them =P)
Date: Thu, 16 Aug 2007 13:05:41 -0400

---- "Jorge Lucángeli Obes" <address@hidden> wrote: 
> I've been giving some thought to Anthony's idea:
> http://kvm.qumranet.com/kvmwiki/Specs/StoringCommandLineInImage
> However, maybe I'm just too much on vacations, but I don't seem to
> come up with a nice way of doing this. Everything keeps coming back to
> creating a new 'container' image format and then implementing block
> layer functions that only add the number of sectors occupied by the
> command-line to the read and write calls made by QEMU, and then just
> relay those calls to the image-specific functions. That doesn't sound
> very efficient.

No, and it fundamentally breaks using a real disk with QEMU.

> The '#!' trick works nice with scripts, but I don't see it playing
> very well with images. ¿Comments? ¿Pointers?

Personally, I'm not sure why we wouldn't just write out the command line
data to a file tied to the primary image file, with some kind of time stamp
to correlate the data from the command line and the last updated time
of the primary image file.  It's intuitive, and doesn't require a bucket of
programming to make work.  The down side is if qemu crashes, the
time stamp between the parameter file and the image file may indicate
the potential for "difference", but this can just be a notice (just as snapshots
used to do with the image files in 0.7.x)

The only hard part  here is when a real physical disk is used with
QEMU since it's harder to make sure the name is valid.



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