Re: [Qemu-devel] Re: [PATCH] rev5: support colon in filenames

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

On Wed, 2009-07-15 at 19:20 +0100, Jamie Lokier wrote:
> Ram Pai wrote:
> > I have verified with relative paths and it works.
> > 
> > After analyzing the code, i came to the conclusion that call to
> > realpath()  adds no real value. 
> > 
> > The logic in bdrv_open2() is something like this
> > 
> > bdrv_open2()
> > {
> >    if (snapshot) {
> >          backup = realpath(filename);
> >          filename=generate_a_temp_file();
> >    }
> >    drv=parse_and_get_bdrv(filename);
> >    drv->bdrv_open(filename);
> >    if (backup) {
> >          bdrv_open2(backup);
> >    }
> > }
> >   
> > in the above function, the call to realpath() would have been useful had
> > it changed the current working directory before calling
> > bdrv_open2(backup). It does not. If in case any function within
> > drv->bdrv_open change the cwd, then I expect them to restore before
> > returning.
> > 
> > Also drv->bdrv_open() can anyway handle relative paths. 
> > 
> > Hence I conclude that the call to realpath() adds no value.
> > 
> > Do you see a flaw in this logic? 
> 
> I don't know about snapshot, but when a qcow2 file contains a relative
> path to it's backing file, QEMU cannot simply open using that relative
> path, because it's relative to the directory containing the qcow2 file,
> not QEMU's current directory.

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. I am pretty sure that the patch would work.
However i have not accumulated enough flight time on qemu; so i can be
wrong :(

And one other thing. Let me know if there a test-suite that I can try
for regressions.

RP

> 
> (That said, I find it quite annoying when renaming qcow2 files that
> there's no easy way to rename their backing files, and it's even worse
> when moving qcow2 files which refer to backing files in another
> directory, and _especially_ when the qcow2 file contains an absolute
> path to the backing file and you're asked to move it to another system
> which doesn't have those directories.)
> 
> -- Jamie
-- 
Ram Pai
System X Device-Driver Enablement Lead
Linux Technology Center
Beaverton OR-97006
503-5783752 t/l 7753752
linuxram@us.ibm.com