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

[Daniel P. Berrange]

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> 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
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