Re: [PATCH] kvmtool: don't rely on $HOME

[Will Deacon <will.deacon@arm.com>]

On Fri, Sep 18, 2015 at 11:51:37AM +0100, Riku Voipio wrote:
> On 17 September 2015 at 18:53, Will Deacon <will.deacon@arm.com> wrote:
> > On Thu, Sep 17, 2015 at 03:03:15PM +0100, Alban Crequy wrote:
> >> kvm__set_dir() called in main() and kvm__get_dir() rely on $HOME. But in
> >> some environments (such as starting lkvm through systemd-run), $HOME is
> >> undefined. This causes bind() to use a socket path containing "(null)"
> >> and this fails. The current code does not check errors returned by
> >> realpath().
> >>
> >> Symptoms:
> >>
> >> | bind: No such file or directory
> >> |   Error: Failed adding socket to epoll
> >> |  Warning: Failed init: kvm_ipc__init
> >> |
> >> |  Fatal: Initialisation failed
> >>
> >> This bug was first reported on https://github.com/coreos/rkt/issues/1393
> >>
> >> Instead of using "$HOME/.lkvm/" (i.e. "/root/.lkvm/"), this patch uses
> >> "/var/lib/lkvm/". This also improve the error reporting by printing the
> >> socket filename.
> >
> > Hmm, but that requires lkvm to be run with sufficient privileges to
> > write to /var/lib, which I don't think is generally the case. I think we
> > have a few options:
> >
> >   (1) Try /var/lib/lkvm if $HOME is NULL
> >   (2) Use an alternative environment variable for the pid prefix
> >   (3) Add a --pid command line option for the pidfile
> >   (4) ???
> >
> > Any preferences? What do other projects do?
> 
> The right place to put a pid file would be $XDG_RUNTIME_DIR aka
> /run/user/$UID/. System services write their pidfiles and sockets to
> plain /run

Ok, that certainly sounds like the right things to do for temporary
structures then. Thanks.

> The place where to put the rootfs structure created in builtin-setup.c
> is more complicated. Is the  created rootfs epheremal? Then sticking
> under /run(user/UID) is fine.

Currently, the filesystem persists across multiple invocations of lkvm,
so I can imagine somebody being surprised if what they thought was
persistent was lost over something like a reboot.

Will