[lxc-devel] [PATCH 2/2] daemon: remove pidfile when daemon container is stopped

[Stéphane Graber]

On Tue, Jan 21, 2014 at 11:33:42AM +0800, Qiang Huang wrote:
> On 2014/1/21 11:20, Stéphane Graber wrote:
> > On Tue, Jan 21, 2014 at 10:54:50AM +0800, Qiang Huang wrote:
> >> Hi Stéphane,
> >>
> >> I'm not sure I understand this.
> >>
> >> In my understanding, anything using the API to control an already
> >> running backgrounded container will use lxc_container_new to create
> >> a new lxc_container, it only share the original one's name and config
> >> and so on. After dealing, will call lxc_container_put to free this
> >> lxc_container, this *new* lxc_container doesn't contain the PID file
> >> information, so it's freeing won't remove PID file.
> > 
> > Hmm, yeah, seems like you're right, I should have rechecked the patch
> > rather than speak from the vague memory of what I saw when you initialy
> > posted it.
> > 
> > 
> > So, re-reading more carefully, I don't completely disagree with the
> > approach, though I don't like having to extend lxc_container just for
> > that...
> 
> Without 1/2 patch, this patch won't work, I'll send new patches.
> So would it be better if I put this into lxc_conf?
> 
> > 
> > There's however one rather big problem, the PID file will contain the
> > wrong PID. The PID being written is getpid() from the parent lxc-start,
> > not the running, forked lxc-start process and that child PID is only
> > known by the start() function in lxccontainer.c, so you can't create the
> > PID file from lxc_start.c
> 
> Yeah, I noticed that before, I thought that's exactly what we want,
> because we can get the init pid of container from lxc_info command.
> 
> If it's not, we can fix it incrementally. :)

No, what I meant is that the PID we are writing is that of a
non-existing process, which makes the pid file entirely useless.

When you start a container, you have at least 3 processes:
 1) The command the user start (lxc-start -d)
 2) The backgrounded fork of that command after start() is done
 3) The container init process

lxc-info and the API init_pid() function gives us (3), what we want to
see in a pidfile is (2) and what we are currently writing is (1).

As (1) exits as soon as the container is started, it's completely
useless as you can't use that to check whether LXC still has control
over the container (i.e. is lxc-start still running in the background).

-- 
Stéphane Graber
Ubuntu developer
http://www.ubuntu.com
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 836 bytes
Desc: Digital signature
URL: <http://lists.linuxcontainers.org/pipermail/lxc-devel/attachments/20140120/ecee4f10/attachment.pgp>