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Eric Blake d1333dd0fb storage: don't follow backing chain symlinks too eagerly 
If you have a qcow2 file /path1/to/file pointed to by symlink
/path2/symlink, and pass qemu /path2/symlink, then qemu treats
a relative backing file in the qcow2 metadata as being relative
to /path2, not /path1/to.  Yes, this means that it is possible
to create a qcow2 file where the choice of WHICH directory and
symlink you access its contents from will then determine WHICH
backing file (if any) you actually find; the results can be
rather screwy, but we have to match what qemu does.

Libvirt and qemu default to creating absolute backing file
names, so most users don't hit this.  But at least VDSM uses
symlinks and relative backing names alongside the
--reuse-external flags to libvirt snapshot operations, with the
result that libvirt was failing to follow the intended chain of
backing files, and then backing files were not granted the
necessary sVirt permissions to be opened by qemu.

See https://bugzilla.redhat.com/show_bug.cgi?id=903248 for
more gory details.  This fixes a regression introduced in
commit 8250783.

I tested this patch by creating the following chain:

ls /home/eblake/Downloads/Fedora.iso # raw file for base
cd /var/lib/libvirt/images
qemu-img create -f qcow2 \
  -obacking_file=/home/eblake/Downloads/Fedora.iso,backing_fmt=raw one
mkdir sub
cd sub
ln -s ../one onelink
qemu-img create -f qcow2 \
  -obacking_file=../sub/onelink,backing_fmt=qcow2 two
mv two ..
ln -s ../two twolink
qemu-img create -f qcow2 \
  -obacking_file=../sub/twolink,backing_fmt=qcow2 three
mv three ..
ln -s ../three threelink

then pointing my domain at /var/lib/libvirt/images/sub/threelink.
Prior to this patch, I got complaints about missing backing
files; afterwards, I was able to verify that the backing chain
(and hence DAC and SELinux relabels) of the entire chain worked.

* src/util/virstoragefile.h (_virStorageFileMetadata): Add
directory member.
* src/util/virstoragefile.c (absolutePathFromBaseFile): Drop,
replaced by...
(virFindBackingFile): ...better function.
(virStorageFileGetMetadataInternal): Add an argument.
(virStorageFileGetMetadataFromFD, virStorageFileChainLookup)
(virStorageFileGetMetadata): Update callers.
 		2013-02-15 16:07:01 -07:00
.gnulib@819b1c38b9 maint: update to latest gnulib 2013-02-01 09:24:00 -07:00
build-aux Document bracket whitespace rules & add syntax-check rule 2012-11-02 14:00:32 +00:00
daemon build: Regenerate man pages on version bump 2013-01-29 13:23:19 +01:00
docs S390: Documentation for CCW address type 2013-02-11 16:27:45 -07:00
examples Remove more trailing semicolons in Python files 2013-02-07 19:52:44 +01:00
gnulib maint: update to latest gnulib 2013-01-02 09:38:30 -07:00
include Introduce API virNodeDeviceLookupSCSIHostByWWN 2013-02-12 00:23:57 +08:00
m4 Fix typo in configure.ac causing $LIBS to gain a copy of $CFLAGS 2013-02-05 18:04:16 +00:00
po Release of libvirt-1.0.2 2013-01-30 10:42:05 +01:00
python Check if classes are derived from object 2013-02-11 18:00:10 +01:00
src storage: don't follow backing chain symlinks too eagerly 2013-02-15 16:07:01 -07:00
tests regex: gnulib guarantees that we have regex support 2013-02-15 13:01:23 -07:00
tools virsh-volume.c: Switch to c99 initialization of vshCmdInfo 2013-02-12 17:50:22 +01:00
.dir-locals.el build: avoid tabs that failed syntax-check 2012-09-06 09:43:46 -06:00
.gitignore util: add virendian.h macros 2013-02-12 09:00:15 -07:00
.gitmodules make .gnulib a submodule 2009-07-08 16:17:51 +02:00
.mailmap Autogenerate AUTHORS 2012-10-19 12:44:56 -04:00
AUTHORS.in Add John Ferlan to the committers list 2013-02-05 10:59:32 -05:00
COPYING.LIB remove all trailing blank lines 2009-07-16 15:06:42 +02:00
ChangeLog-old virterror.c: Fix several spelling mistakes 2012-02-03 11:32:51 -07:00
HACKING Turn virSecurityManager into a virObjectLockable 2013-02-11 12:33:41 +00:00
Makefile.am build: Fix AUTHORS generation 2012-12-17 21:17:55 +01:00
Makefile.nonreentrant Ban use of all inet_* functions 2010-10-22 11:59:23 +01:00
README Correct typos in the documentation (Atsushi SAKAI) 2008-01-24 10:15:13 +00:00
README-hacking maint: relax git minimum version 2010-02-24 14:29:27 -05:00
TODO Update todo list file to point at bugzilla/website 2010-10-13 16:45:26 +01:00
autobuild.sh Switch automated builds to use Mingw64 toolchain instead of Mingw32 2012-06-25 10:41:10 +01:00
autogen.sh build: fix incremental autogen.sh when no AUTHORS is present 2012-12-03 14:59:09 -07:00
bootstrap maint: update to latest gnulib 2013-02-01 09:24:00 -07:00
bootstrap.conf build: more mingw fixes 2013-02-15 15:45:52 -07:00
cfg.mk hacking: Add some details to handle Valgrind output 2013-02-07 14:08:14 -05:00
configure.ac Release of libvirt-1.0.2 2013-01-30 10:42:05 +01:00
libvirt.pc.in build: silence warning from autoconf 2012-05-30 09:22:02 -06:00
libvirt.spec.in spec: Fix minor changelog issues 2013-02-05 10:00:32 +01:00
mingw-libvirt.spec.in spec: indent %if to make it easier to see conditions 2013-01-21 10:36:14 -07:00
run.in Add a virtlockd client as a lock driver impl 2012-12-13 15:26:57 +00:00

README 

         LibVirt : simple API for virtualization

  Libvirt is a C toolkit to interact with the virtualization capabilities
of recent versions of Linux (and other OSes). It is free software
available under the GNU Lesser General Public License. Virtualization of
the Linux Operating System means the ability to run multiple instances of
Operating Systems concurrently on a single hardware system where the basic
resources are driven by a Linux instance. The library aim at providing
long term stable C API initially for the Xen paravirtualization but
should be able to integrate other virtualization mechanisms if needed.

Daniel Veillard <veillard@redhat.com>