[Qemu-devel] backing_file Path

[Zhi Hui Li <zhihuili@linux.vnet.ibm.com>]

when I trace the code of qemu-img.c， I found in the image file, the 
backing_file use the relative path, I think Maybe it has some problems.

for example:

1: qemu-img create -o backing_file=../xxxx aa.img 5G

2: qemu-system-x86_64   aa.img

if you change aa.img's the path, the exec is wrong,it can't find the 
backing_file path, because the backing_file use the relative path,
Could we change the relative path to the absolute path?