Le vendredi 25 janvier 2008 Ã 09:18 -0600, Anthony Liguori a Ãcrit :
> Laurent Vivier wrote:
> > Hi,
> > this patch allows to mount qemu disk images on the host.
Sorry, I didn't see you did a similar work 19 months ago.
> Note, the general problem with this approach is that mounting a NBD
> device locally with write access can lead to dead locks. If you look
> through the mailing list archives, you'll find a number of conversations
> on the topic.
Yes, I experimented some problems with heavily loaded I/O (2 * dbench 64
on a 4 CPUs SMP)
But perhaps to edit config files or fsck partition of a virtual machine
it is acceptable.
What I'm wondering is how loop and device mapper can work ?
> Anthony Liguori
> > It is based on the Network Block Device protocol and allows qemu-img to
> > become an NBD server (Yes, Anthony, userspace block device is the right
> > way to do that... :-P ).
> > Once you've applied the attached patch to Qemu and build the binaries,
> > you can use it like that:
> > # ./qemu-img server -d 1234 etch.qcow2
> > This starts an NBD server on port 1234. This server will expose
> > the disk image etch.qcow2. "-d" means it will be daemonize and will run
> > in background.
> > Then you need to connect the block device to the server:
> > # nbd-client localhost 1234 /dev/nbd0
> > Negotiation: ..size = 4194304KB
> > bs=1024, sz=4194304
> > This will link etch.qcow2 to /dev/nbd0.
> > Then to see partitions, you can use kpartx, as explained Daniel, or my
> > patched loop modules (I can send an updated and bug free version).
> > ...
> > # kpartx -a /dev/nbd0
> > ...
> > or
> > ...
> > # rmmod loop
> > # insmod drivers/block/loop.ko max_part=64
> > # losetup -f /dev/nbd0
> > ...
> > # mount /dev/loop0p1 /mnt
> > # ls /mnt
> > bench cdrom etc initrd.img media proc selinux tmp vmlinuz
> > bin clients home lib mnt root srv usr
> > boot dev initrd lost+found opt sbin sys var
> > # cd
> > # umount /mnt
> > # losetup -d /dev/loop0
> > # nbd-client -d /dev/nbd0
> > TODO: security/host client checking, device lock...
> > As usual all comments are welcome,
> > have fun,
> > Laurent
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