[lxc-devel] [PATCH] pass lxcpath to lxc_command

[Serge Hallyn]

Quoting Stéphane Graber (stgraber at ubuntu.com):
> On 02/11/2013 03:43 PM, Serge Hallyn wrote:
> > 
> > The previous lxcpath patches added support for a custom LXCPATH set
> > through a system-wide configuration file.
> > 
> > This was also exposed through the C api, so that a custom lxcpath could
> > be set at the container object instanciation time, or set at runtime.
> > 
> > However the command sock filename was always located under the global
> > lxcpath, which could be confusing, and would be a problem for users
> > with insufficient perms to the system-wide lxc path (i.e. if setting
> > lxcpath to $HOME/lxcbase).  This patch changes that by passing the
> > lxcpath to all callers of lxc_command().
> > 
> > It remains to add an lxcpath command line argument to most of the
> > command line tools (which are not using the C api) - lxc-start,
> > lxc-info, lxc-stop, etc.
> > 
> > At this point it becomes tempting to do something like
> > 
> > 	c = lxc.Container("r1", "/var/lib/lxc")
> > 	c2 = lxc.Container("r1", "$HOME/lxcbase")
> > 
> > However, that's problematic - those two will use the same directory
> > names for cgroup directories.
> > 
> > What would be the best way to handle this?  One way (which I kind
> > of like) is to give up on naming the cgroups after the container.
> > use mkstemp for the cgroup name, let lxc keep track of the cgroup
> > name based on the command socket, and make users use lxc-cgroup to get
> > and change settings.
> 
> As we discussed on IRC, I think it'd be best to do two things:
> 1) Add a new lxc.cgroup.directory option which would default to "lxc"
> (our current directory) and let people easily override to another name
> to avoid the conflict.
> 2) Add a simple conflict checker in the cgroup code. If the cgroup path
> already exists, then simply prefix -X to the directory name,
> incrementing X as needed.

Sounds good.  The main thing we'll need (in either case) is to have a
lxc_cgroup_callback, analogous to lxc_pid_callback, in start.c which can
return the name of a cgroup if asked by a new LXC_COMMAND_CGROUP_NAME.

-serge