On 11/15/2013 09:42 AM, Max Reitz wrote: > Actually, the same problem can occur anyway if you have a path with a > couple of “.” and “..” in it – or even just a hardlink. Thus, to be > completely safe, we'd have to check whether the snapshot file (if it > already exists) has a different inode number and/or is located on a > different filesystem.
See also the recent thread on detecting backing file loops - this should be part of that solution (if it isn't already): https://lists.gnu.org/archive/html/qemu-devel/2013-11/msg01840.html Backing file loops might get away with string-only detection; but then I start to worry that the string-only detection will misbehave on relative paths (consider: /dir1/a <- /dir1/b [backed by relative 'a'] <- /dir2/a [backed by absolute /dir1/b] <- /dir2/a [backed by relative 'a']); devno/inode pairs are the only reliable to detect loops when only the filesystem is involved, but then you also introduce network protocols (and there, it's worse: gluster://host1/vol/img and gluster://host2/vol/img could be the same file, if host1 and host2 are part of the same storage cluster, but there is no devno/inode to tell you that). -- Eric Blake eblake redhat com +1-919-301-3266 Libvirt virtualization library http://libvirt.org
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