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From: | Anthony Liguori |
Subject: | Re: [Qemu-devel] [PATCH] block: fix the use of protocols in backing files |
Date: | Thu, 28 Oct 2010 09:10:30 -0500 |
User-agent: | Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.12) Gecko/20100915 Lightning/1.0b1 Thunderbird/3.0.8 |
On 10/28/2010 04:51 AM, Daniel P. Berrange wrote:
The problem is that this wouldn't work in the general case. It's rather an exception that it makes sense for file: backing files with file: images. Consider this: # qemu-img create -o backing_file=nbd:foo:1234 /tmp/main.img Without this patch, you'll end up with /tmp/nbd:foo:1234, which is probably not what you wanted. With a patch that would work for file: you would get a hardly better path nbd:/tmp/foo:1234Since we know the protocol, there could be a per-protocol function used for resolving the backing store URI relative to the master URI. That would avoid needing to special case file: in the shared generic code.
Relative resolution of a backing files makes me very nervous. Any time a disk image can reasonably resolve to something other than what the user expected is potentially a very nasty security issue.
The less obvious the resolution, the worse the problem becomes. I think resolution based on current path is probably the most obvious implementation.
Regards, Anthony Liguori
Daniel
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