Re: [Qemu-devel] [PATCH 4/4][RFC] Add logic to QEMU to read command line options from qcow2 images

[Philip Boulain <prb@ecs.soton.ac.uk>]

Anthony Liguori wrote:
> Philip Boulain wrote:
>> That should probably be "#!/usr/bin/env qemu", or something similar...
> I think the magic should just be "#!".  Whatever you put as the QEMU 
> executable is your choice.  Separating the args to the next line 
> actually does make it pretty portable.

Not really; you'd still have to use the editing tool (qemu-img?) to prep it for 
your particular QEMU binary location on that particular host. But, yes: being 
able to set arbitrary binaries is essential. Using env is probably a good 
/default/, though.

> Yes, I think that another argument should be required as Dan suggested 
> although I'd like something more explicit like "-read-args-from-image".  
> In the case where the image was directly executable, it would be 
> embedded as part of the interpreter arguments.

This works, so long as qemu disregards "-read-args-from-image" unless it's 
being called as an interpreter. Otherwise, you've put the lock and the key in 
the same place. :)

If an image says:
   #!/whatever/qemu -read-args-from-image
   -curious-and-interesting-flags

This should use those flags:
   $ ./image.qcow2

And this shouldn't, because you don't need to have made it executable:
   $ qemu -hda image.qcow2

(But this would:)
   $ qemu -read-args-from-image -hda image.qcow2

(Side thought: presumably, we're assuming that the in-file and on-command-line 
arguments are unioned, ideally with the latter taking precidence if mutually 
exclusive.)

>> This also doesn't apply outside of UNIX-like environments, e.g. 
>> Windows...
> I think this is covered by requiring the additional argument.

Agreed.

LionsPhil