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Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Int

From: Richard W.M. Jones
Subject: Re: [Qemu-devel] [RFC] block-trace Low Level Command Supporting Disk Introspection
Date: Wed, 22 May 2013 17:42:19 +0100
User-agent: Mutt/1.5.20 (2009-12-10)

On Wed, May 22, 2013 at 11:51:16AM -0400, Wolfgang Richter wrote:
> This is actually interesting.  Does the QEMU nbd server support multiple
> readers?

Yes.  qemu-nbd has a -e/--shared=<N> option which appears to do
exactly what it says in the man page.

$ guestfish -N fs exit
$ ls -lh test1.img 
-rw-rw-r--. 1 rjones rjones 100M May 22 17:37 test1.img
$ qemu-nbd -e 3 -r -t test1.img

>From another shell:

$ guestfish --format=raw -a nbd://localhost

Welcome to guestfish, the guest filesystem shell for
editing virtual machine filesystems and disk images.

Type: 'help' for help on commands
      'man' to read the manual
      'quit' to quit the shell

><fs> run
><fs> list-filesystems 
/dev/sda1: ext2

Run up to two extra guestfish instances, with the same result.  The
fourth guestfish instance hangs at the 'run' command until one of the
first three is told to exit.


Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
virt-top is 'top' for virtual machines.  Tiny program with many
powerful monitoring features, net stats, disk stats, logging, etc.

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