Re: qcow2 relative paths (was: [PATCH] rev5: support colon in filenames)

[Ram Pai <linuxram@us.ibm.com>]

On Wed, 2009-07-15 at 22:04 +0100, Jamie Lokier wrote:
> Ram Pai wrote:
> > I have successfully verified qcow2 files. But then I may not be trying
> > out the exact thing that you are talking about. Can you give me a test 
> > case that I can verify.
> 
> Commands tried with qemu-0.10.0-1ubuntu1:
> 
> $ mkdir unlikely_subdir
> $ cd unlikely_subdir
> $ qemu-img create -f qcow2 backing.img 10
> Formatting 'backing.img', fmt=qcow2, size=10 kB
> $ qemu-img create -f qcow2 -b ../unlikely_subdir/backing.img main.img 10
> Formatting 'main.img', fmt=qcow2, backing_file=../unlikely_subdir/backing.img, size=10 kB
> $ cd ..
> $ qemu-img info unlikely_subdir/main.img 
> image: unlikely_subdir/main.img
> file format: qcow2
> virtual size: 10K (10240 bytes)
> disk size: 16K
> cluster_size: 4096
> highest_alloc: 16384
> backing file: ../unlikely_subdir/backing.img (actual path: unlikely_subdir/../unlikely_subdir/backing.img)
> 
> See especially the "actual path" line.
> 
> $ mv unlikely_subdir other_subdir
> $ ls -l other_subdir
> total 32
> -rw-r--r-- 1 jamie jamie 16384 2009-07-15 21:59 backing.img
> -rw-r--r-- 1 jamie jamie 16384 2009-07-15 21:59 main.img
> $ qemu-img info other_subdir/main.img 
> qemu-img: Could not open 'other_subdir/main.img'

Turns out that I did introduce a bug by deleting the call
to path_combine() before calling bdrv_open() on the backing
filename. However the call to realpath() is still not needed.
It feels like a kludge introduced to stop path_combine() from
munging backing_filename. 

I will send out yet another revision with the fix. I just dont' know
what else I will be breaking without having a regression test
harness. :( 


> 
> What an unhelpful error message...  There isn't even a way to find out
> the backing file path which the tool is looking for.

Ok. i have introduced a message towards the effect, in the next revision
of the patch.  Hope that will make things a little easier.

I have to go through the all the other mails to understand what has been
proposed, and what I need to incorporate. Looks like a tall order.

For now i will send out revision 6 in the next few hours.

RP


> 
> > And one other thing. Let me know if there a test-suite that I can try
> > for regressions.
> 
> Sorry, I don't know anything about any QEMU test suites.
> 
> -- Jamie

RP