[libvirt] [PATCH] Allow use of file images for LXC container filesystems

Eric Blake eblake at redhat.com
Tue Sep 27 23:27:42 UTC 2011

On 08/04/2011 09:41 AM, Daniel P. Berrange wrote:
> From: "Daniel P. Berrange"<berrange at redhat.com>
> A previous commit gave the LXC driver the ability to mount
> block devices for the container filesystem. Through use of
> the loopback device functionality, we can build on this to
> support use of plain file images for LXC filesytems.
> By setting the LO_FLAGS_AUTOCLEAR flag we can ensure that
> the loop device automatically disappears when the container
> dies / shuts down

> +static int lxcSetupLoopDevice(virDomainFSDefPtr fs)
> +{
> +    int lofd = -1;
> +    int fsfd = -1;
> +    struct loop_info64 lo;
> +    char *loname = NULL;
> +    int ret = -1;
> +
> +    if ((lofd = lxcGetLoopFD(&loname))<  0)
> +        return -1;
> +
> +    memset(&lo, 0, sizeof(lo));
> +    lo.lo_flags = LO_FLAGS_AUTOCLEAR;

The kernel headers available on RHEL 5 or CentOS 5 lack this enum value, 
which causes compilation to fail if you are trying to build lxc support 
for these older systems.  When I have some time, I will probably just 
write a patch that adds a configure.ac probe for LO_FLAGS_AUTOCLEAR, and 
where it is missing, make any attempt to do plan9 file system 
passthrough to lxc guests fail since they are unsupported on these old 
kernels.  You should still be able to use the other aspects of lxc that 
don't involve file system passthrough, although obviously lxc isn't 
getting much testing on these older systems.

Eric Blake   eblake at redhat.com    +1-801-349-2682
Libvirt virtualization library http://libvirt.org

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