1 files changed, 80 insertions, 0 deletions
diff --git a/results/classifier/118/debug/1524546 b/results/classifier/118/debug/1524546
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+semantic: 0.938
+virtual: 0.929
+mistranslation: 0.921
+register: 0.917
+graphic: 0.903
+assembly: 0.895
+architecture: 0.889
+socket: 0.887
+boot: 0.885
+peripherals: 0.885
+VMM: 0.877
+performance: 0.872
+arm: 0.869
+x86: 0.865
+device: 0.861
+PID: 0.852
+risc-v: 0.847
+hypervisor: 0.841
+permissions: 0.834
+user-level: 0.831
+files: 0.830
+KVM: 0.824
+kernel: 0.817
+vnc: 0.796
+network: 0.772
+TCG: 0.770
+ppc: 0.738
+i386: 0.712
+
+qemu-img rebase error message mentions wrong file name
+
+While doing 'qemu-img rebase' for linking to a different backing file, if the old backing file does not exist, the command fails. During this failure, the error message shown is misleading.
+e.g. qemu-img rebase -b <backing_file> <filename> throws error saying "Could not open <filename>"
+Ideally it should "Could not open <old_backing_file>"
+
+snippet -
+[root@oxy-dev ~]# qemu-img info /opt/stack/data/nova/instances/94864a64-ebf8-45e6-a777-615921216a0a/disk
+image: /opt/stack/data/nova/instances/94864a64-ebf8-45e6-a777-615921216a0a/disk
+file format: qcow2
+virtual size: 20G (21474836480 bytes)
+disk size: 174M
+cluster_size: 65536
+backing file: /tmp/3559241a79b79ae663ec6e3d9b75d469967b383b
+Format specific information:
+    compat: 1.1
+    lazy refcounts: false
+[root@oxy-dev ~]# mv /tmp/3559241a79b79ae663ec6e3d9b75d469967b383b /tmp/3559241a79b79ae663ec6e3d9b75d469967b383a
+[root@oxy-dev ~]# file !$
+file /tmp/3559241a79b79ae663ec6e3d9b75d469967b383a
+/tmp/3559241a79b79ae663ec6e3d9b75d469967b383a: x86 boot sector; partition 1: ID=0x83, active, starthead 32, startsector 2048, 409600 sectors; partition 2: ID=0x8e, starthead 159, startsector 411648, 16365568 sectors, code offset 0xc0
+[root@oxy-dev ~]# file /tmp/3559241a79b79ae663ec6e3d9b75d469967b383b
+/tmp/3559241a79b79ae663ec6e3d9b75d469967b383b: cannot open (No such file or directory)
+[root@oxy-dev ~]# qemu-img rebase -b /tmp/3559241a79b79ae663ec6e3d9b75d469967b383a /opt/stack/data/nova/instances/94864a64-ebf8-45e6-a777-615921216a0a/disk
+qemu-img: Could not open '/opt/stack/data/nova/instances/94864a64-ebf8-45e6-a777-615921216a0a/disk': Could not open file: No such file or directory
+[root@oxy-dev ~]# 
+qemu-img version 1.5.3
+OS: RHEL7 - 3.10.0-229
+libvirtd (libvirt) 1.2.8
+
+I'm pretty sure this is working as intended.
+If you observe the code, qemu-img first opens filename. When qemu opens a file, it needs full access to it's chain of backing files - Hence, if the old backing file does not exist, opening filename fails.
+
+(Not an active qemu dev, just passing through)
+
+The full story is that in 2015, qemu probably did not note that it failed to open the overlay (<filename>) because it failed to open the backing file.  It does that, now, though:
+
+$ qemu-img rebase -b new.qcow2 top.qcow2 
+qemu-img: Could not open 'top.qcow2': Could not open backing file: Could not open 'base.qcow2': No such file or directory
+
+So that should be a fix.
+
+Max
+
+What to do if the old file has been moved? 
+
+Say the backing file was /path/to/os.qcow2 and it was moved to /new/path/to/os.qcow2.
+
+How can we tell snapshot.qcow2 to update the backing file from /path/to/os.qcow2 to /new/path/to/os.qcow2?
+