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H A Dblock.cdiff d80ac658f2caacfb14ea386211c4a9bea0cea280 Wed Jan 08 13:43:25 CST 2014 Peter Feiner <peter@gridcentric.ca> block: fix backing file segfault

When a backing file is opened such that (1) a protocol is directly
used as the block driver and (2) the block driver has bdrv_file_open,
bdrv_open_backing_file segfaults. The problem arises because
bdrv_open_common returns without setting bd->backing_hd->file.

To effect (1), you seem to have to use the -F flag in qemu-img. There
are several block drivers that satisfy (2), such as "file" and "nbd".
Here are some concrete examples:

#!/bin/bash

echo Test file format
./qemu-img create -f file base.file 1m
./qemu-img create -f qcow2 -F file -o backing_file=base.file\
file-overlay.qcow2
./qemu-img convert -O raw file-overlay.qcow2 file-convert.raw

echo Test nbd format
SOCK=$PWD/nbd.sock
./qemu-img create -f raw base.raw 1m
./qemu-nbd -t -k $SOCK base.raw &
trap "kill $!" EXIT
while ! test -e $SOCK; do sleep 1; done
./qemu-img create -f qcow2 -F nbd -o backing_file=nbd:unix:$SOCK\
nbd-overlay.qcow2
./qemu-img convert -O raw nbd-overlay.qcow2 nbd-convert.raw

Without this patch, the two qemu-img convert commands segfault.

This is a regression that was introduced in v1.7 by
dbecebddfa4932d1c83915bcb9b5ba5984eb91be.

Signed-off-by: Peter Feiner <peter@gridcentric.ca>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff dbecebddfa4932d1c83915bcb9b5ba5984eb91be Sun Sep 22 07:05:06 CDT 2013 Fam Zheng <famz@redhat.com> block: fix backing file overriding

Providing backing.file.filename doesn't override backing file as expected:

$ x86_64-softmmu/qemu-system-x86_64 -drive \
file=/tmp/child.qcow2,backing.file.filename=/tmp/fake.qcow2

qemu-system-x86_64: -drive \
file=/tmp/child.qcow2,backing.file.filename=/tmp/fake.qcow2: could not
open disk image /tmp/child.qcow2: Can't specify 'file' and 'filename'
options at the same time

With

$ qemu-img info /tmp/child.qcow2
image: /tmp/child.qcow2
file format: qcow2
virtual size: 1.0G (1073741824 bytes)
disk size: 196K
cluster_size: 65536
backing file: /tmp/fake.qcow2

This fixes it by calling bdrv_get_full_backing_filename only if
backing.file.filename is not provided. Also save the backing file name
to bs->backing_file so the information is correct with HMP "info block".

Signed-off-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>