[Libguestfs] question about backing file path of a qcow2 image

[bigclouds]

thanks . now i know qcow2 only store relative path.
look at my error message,  6a3256bb-b247-4fb5-9f75-8ffa7151eeda  i a symlink to a LV. it is the backing_file of several images(LV)..
i have no idea of  the reason of the error.

# virt-win-reg 6a3256bb-b247-4fb5-9f75-8ffa7151eeda 'HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion' 'Productname'
hivex: /tmp/libguestfsIdLWuF/0-software: trailing garbage at end of file (at 0x86e000, after 2088 pages)
hivex_open: Operation not supported at /usr/bin/virt-win-reg line 259.
#qemu-img info 6a3256bb-b247-4fb5-9f75-8ffa7151eeda
image: 6a3256bb-b247-4fb5-9f75-8ffa7151eeda
file format: raw
virtual size: 10G (10737418240 bytes)
disk size: 0
#ls -l 6a3256bb-b247-4fb5-9f75-8ffa7151eeda
lrwxrwxrwx. 1 vdsm kvm 78 Sep 11 13:54 6a3256bb-b247-4fb5-9f75-8ffa7151eeda -> /dev/28da8f65-abe7-4ffd-a16d-9155d12a8d72/6a3256bb-b247-4fb5-9f75-8ffa7151eeda




At 2013-09-11 20:38:59,"Richard W.M. Jones" <rjones at redhat.com> wrote:
>On Wed, Sep 11, 2013 at 10:33:06AM +0800, bigclouds wrote:
>> hi,all
>> images of qcow2 format with backing files, its backing files have
>> two path infos (absolute path and relative path),
>
>This is not true.  The file format only contains the relative path.
>qemu-img info will print an absolute path, but it's not stored inside
>the file.
>
>> how to let
>> libguestfs use absolute path rather than relative path. in some
>> case, this leads error.
>
>It's hard to know what the problem is you're describing since you give
>no details at all.  But anyway ...
>
>Libguestfs doesn't actually use or care about the backing file of
>qcow2 files.  That is entirely handled by qemu when it opens the qcow2
>file.
>
>There are three problems I know about:
>
>(1) If your backing file is located on tmpfs, then qemu can have
>    problems opening the file.  This is fixed upstream (commit
>    749e947bb010 / RHBZ#994517).
>
>(2) If your disk image refers to the backing file by its relative path
>    then it may not work if you move it around.  This should be
>    obvious, but seems to cause people enough trouble.
>
>(3) Certain characters in filenames may be forbidden (esp. ':') or may
>    require quoting (',').  Libguestfs (recent versions, anyhow)
>    should always do the right thing when it encounters one of these
>    characters.  If not, file a bug.
>
>The solution to (2) is to always use absolute paths to files and/or
>not to move files around.
>
>So long as you don't move the file around, qemu handles the case where
>it is started from a different directory.  It searches for the backing
>file relative to the location of the qcow2 file, NOT relative to the
>current directory.
>
>If you find some other problem, please show us a clear reproducer and
>include all of the debugging and error messages:
>
>http://libguestfs.org/guestfs-faq.1.html#debug
>
>Rich.
>
>-- 
>Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
>libguestfs lets you edit virtual machines.  Supports shell scripting,
>bindings from many languages.  http://libguestfs.org
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