Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system

[Stefan Hajnoczi <stefanha@gmail.com>]

On Fri, Jan 11, 2013 at 03:27:52PM +0800, 马磊 wrote:
> On Fri, Jan 11, 2013 at 2:28 PM, Wanlong Gao <gaowanlong@cn.fujitsu.com>wrote:
> 
> > On 01/11/2013 11:39 AM, 马磊 wrote:
> > >
> > >
> > > On Thu, Jan 10, 2013 at 8:20 PM, Daniel P. Berrange <berrange@redhat.com<mailto:
> > berrange@redhat.com>> wrote:
> > >
> > >     On Wed, Jan 09, 2013 at 09:37:54PM +0000, Blue Swirl wrote:
> > >     > On Wed, Jan 9, 2013 at 7:31 AM, 马磊 <aware.why@gmail.com <mailto:
> > aware.why@gmail.com>> wrote:
> > >     > >
> > >     > >
> > >     > >>> Hi,
> > >     > >>>     The final effect is as follows:
> > >     > >>>
> > >     > >>>
> > >     > >>> [malei@xentest-4-1 Fri Dec 28 ~/honeypot/xen/xen-4.1.2]$
> > qemu-img-xen cat
> > >     > >>> -f /1/boot.ini ~/vm-check.img
> > >     > >>> [boot loader]
> > >     > >>> timeout=30
> > >     > >>> default=multi(0)disk(0)rdisk(0)partition(1)\WINDOWS
> > >     > >>> [operating systems]
> > >     > >>> multi(0)disk(0)rdisk(0)partition(1)\WINDOWS="Microsoft Windows
> > XP
> > >     > >>> Professional" /noexecute=optin /fastdetect
> > >     > >>>
> > >     > >>> [malei@xentest-4-1 Fri Dec 28 ~/honeypot/xen/xen-4.1.2]$
> > qemu-img-xen ls
> > >     > >>> -l -d /1/ ~/vm-check.img
> > >     > >>> 【name                 size(bytes) dir?      date
> > >     > >>> create-time】
> > >     > >>> AUTOEXEC.BAT 0                file 2010-12-22        17:30:37
> > >     > >>> boot.ini               211                file 2010-12-23
> >    01:24:41
> > >     > >>> bootfont.bin  322730                file 2004-11-23
> >  20:00:00
> > >     > >>>
> > >     > >>>
> > >     > >>>
> > >     > >>> As you see above, the patch add two sub-commands for
> > qemu-img-xen：cat and
> > >     > >>> ls.
> > >     > >>>
> > >     > >>> For details in the patch, please check the attachment.
> > >     > >>>
> > >     > >>>
> > >     > >
> > >     > > Does anyone prefer this feature?!
> > >     >
> > >     > Nice feature, but this approach would just clutter QEMU and give
> > only
> > >     > readonly FAT or NTFS support. I think a more generally useful
> > approach
> > >     > would be to use NBD or iSCSI to export the block device data from
> > the
> > >     > image file (qemu-nbd already exists) and then make a tool that uses
> > >     > some combination of NBD/iSCSI client, all GRUB file systems and
> > FUSE
> > >     > or other user space methods to access the contents of the
> > filesystem.
> > >     > Probably also UML with a simple guest agent could provide
> > read/write
> > >     > access to any file system that Linux supports.
> > >
> > >     The latter is what libguestfs already provides. It boots a Linux
> > kernel
> > >     and mini initrd containing a guest agent, to provide APIs to do
> > arbitrary
> > >     manipulation of guest OS images.
> > >
> > >     The reason libguestfs used a linux guest was precisely to avoid
> > having
> > >     to re-implement drivers for every filesystem in existance like this
> > >     patch is trying todo.
> > >
> > >     I don't think QEMU wants to be in the business of maintaining
> > filesystem
> > >     drivers, so I'd reject this proposed patch.
> > >
> > >     Regards,
> > >     Daniel
> > >     --
> > >     |: http://berrange.com      -o-
> > http://www.flickr.com/photos/dberrange/ :|
> > >     |: http://libvirt.org              -o-
> > http://virt-manager.org :|
> > >     |: http://autobuild.org       -o-
> > http://search.cpan.org/~danberr/ :|
> > >     |: http://entangle-photo.org       -o-
> > http://live.gnome.org/gtk-vnc :|
> > >
> > >
> > >
> > > This feature could be configured to be optional in make file
> > configuration according to individual preference.
> > > _In addition, the fat32 and ntfs filesystem driver will not change for a
> > long time so it needs no much maintainence  once implemented._
> >
> > As Daniel and Stefan said, you can try to use libguestfs [libguestfs.org]
> > and qemu-nbd.
> > In libguestfs, we provide virt-cat, virt-ls, etc. And support all the disk
> > type which QEMU supported.
> >
> > Thanks,
> > Wanlong Gao
> >
> >
> *I used libguest, it's startup takes too long to meet specific requirements
> under some time-sensitive circumstance. *

Then use qemu-nbd instead.  It's fast and you can use all the file
systems supported by your host (ext4, xfs, fat, ntfs, etc), as well as
LVM or encrypted volumes.

Stefan