[Qemu-devel] [RFC] Check backing_file chain's loop

[Dongxu Wang <wdongxu@linux.vnet.ibm.com>]

Hi,

Now block layer does not check whether backing_file chain can be a 
circle, do you think it is necessary to do a check?

For example,  1.qcow2's backing_file is 2.qcow2 and 2.qcow2's 
backing_file is 1.qcow2, then any IO operation will be a fault.

If necessary, I will post a patch to fix.

[$] qemu-img create -f qcow2 1.qcow2
qemu-img: Image creation needs a size parameter
[$] qemu-img create -f qcow2 1.qcow2 8M
Formatting '1.qcow2', fmt=qcow2 size=8388608 encryption=off 
cluster_size=65536 lazy_refcounts=off
[$] qemu-img create -f qcow2 2.qcow2 -o backing_file=1.qcow2
Formatting '2.qcow2', fmt=qcow2 size=8388608 backing_file='1.qcow2' 
encryption=off cluster_size=65536 lazy_refcounts=off
[$] qemu-img create -f qcow2 1.qcow2 -o backing_file=2.qcow2
Formatting '1.qcow2', fmt=qcow2 size=8388608 backing_file='2.qcow2' 
encryption=off cluster_size=65536 lazy_refcounts=off
[$] qemu-io -c "read -v 0 512" 1.qcow2
^CSegmentation fault (core dumped)



Thanks.