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Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk fo
From: |
Blue Swirl |
Subject: |
Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system |
Date: |
Thu, 17 Jan 2013 20:22:40 +0000 |
On Mon, Jan 14, 2013 at 9:13 AM, Stefan Hajnoczi <address@hidden> wrote:
> On Sat, Jan 12, 2013 at 12:00:45PM +0000, Blue Swirl wrote:
>> On Fri, Jan 11, 2013 at 7:27 AM, 马磊 <address@hidden> wrote:
>> >
>> >
>> > On Fri, Jan 11, 2013 at 2:28 PM, Wanlong Gao <address@hidden>
>> > wrote:
>> >>
>> >> On 01/11/2013 11:39 AM, 马磊 wrote:
>> >> >
>> >> >
>> >> > On Thu, Jan 10, 2013 at 8:20 PM, Daniel P. Berrange <address@hidden
>> >> > <mailto:address@hidden>> 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 <address@hidden
>> >> > <mailto:address@hidden>> wrote:
>> >> > > >
>> >> > > >
>> >> > > >>> Hi,
>> >> > > >>> The final effect is as follows:
>> >> > > >>>
>> >> > > >>>
>> >> > > >>> address@hidden 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
>> >> > > >>>
>> >> > > >>> address@hidden 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.
>>
>> For maximum speed, the backing formats (QCOW etc) should be
>> implemented in the kernel directly, somewhat like device mapper or
>> /dev/loop device.
>>
>> A very simple and fast approach without any changes would be to
>> convince the guest to not to use partitions and instead use one file
>> system for an entire block device, then the backing file (in raw
>> format, no QCOW etc) could be manipulated by mounting it with the
>> loopback device.
>>
>> Alternatively, we could implement in QEMU a way to concatenate several
>> separate files into one, each of the files containing a partition or
>> some space for partition table. Then the files could be again accessed
>> with loopback mount. The partition table could be also synthesized.
>>
>> I don't know why the loopback mount in the kernel does not support
>> partitions, that would also solve the problem when using raw files.
>
> The loop module supports partitions through the offset= parameter.
>
> For example:
>
> # fdisk -lu /dev/sda
> [...]
> Device Boot Start End Blocks Id System
> /dev/sda1 * 2048 1026047 512000 83 Linux
> /dev/sda2 1026048 500117503 249545728 83 Linux
> # mount -o loop,offset=$((2048 * 512)) /dev/sda /mnt/boot # mount sda1
Doesn't this make also the space after sda1, up to end of the device
accessible via the partition? It could be a problem if the file system
in sda1 (due to a bug) referenced blocks in sda2, or someone did dd
if=/dev/zero of=/dev/loop0 to clear the partition.
>
> Stefan
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, (continued)
Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Daniel P. Berrange, 2013/01/10
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, 马磊, 2013/01/10
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Wanlong Gao, 2013/01/11
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, 马磊, 2013/01/11
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Stefan Hajnoczi, 2013/01/11
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Blue Swirl, 2013/01/12
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Wanlong Gao, 2013/01/13
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Stefan Hajnoczi, 2013/01/14
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system,
Blue Swirl <=
- Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Stefan Hajnoczi, 2013/01/18
Re: [Qemu-devel] [PATCH] reading files from qcow2-formated image disk for windows system, Stefan Hajnoczi, 2013/01/10