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Re: [Qemu-devel][PATCH] qemu-fuse


From: Anthony Liguori
Subject: Re: [Qemu-devel][PATCH] qemu-fuse
Date: Wed, 27 Aug 2008 11:28:37 -0500
User-agent: Thunderbird 2.0.0.16 (X11/20080723)

Shahar Frank wrote:
Hi All,

        The attached is a small utility to mount qemu images as pseudo
partition files. It can be very useful to access (rw) images from the
host.
I would not use it for production, but it seems to be stable.

Heh, quite similar to:

http://hg.codemonkey.ws/qemu-img-mount/file/9f11265882b3/qemu-img-mount.diff

So this was my first approach to solving this problem that I ended up abandoning in favor of qemu-nbd (which is now in the tree). The main limitation I found with fuse is that by default (and it takes a lot to change this), fuse filesystems are unreadable by root. This means that you cannot easily mount -oloop something in a fuse filesystem.

What I really wanted, was the ability to say something like:

qemu-img mount -p1 foo.img /mnt

and it would Just Work. The only two options I found that could make this work is:

1) disable the root readable limitation in fuse, this has to be done globally and I suspect is unlikely to be done by distros.

2) add support to qemu-img-mount to use filesystems libraries like libe2fs to read and present the filesystem contents. This has the advantage of working entirely as the user who issues the command but has the disadvantage of requiring a lot of effort without being able to support all filesystems that Linux supports.

So that's why I settled on qemu-nbd.

Regards,

Anthony Liguori





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