[lxc-devel] [RFC 0/5] stop hook with namespace access

[Serge Hallyn]

So long as there are no other changes, please add my Acked-by
when you add your Signed-off-by (to the ones I acked)

Quoting Stéphane Graber (stgraber at ubuntu.com):
> Hi,
> 
> Please note that even though Serge acked most of this patchset, I won't
> be pushing it until it's re-sent with all commits including the required
> Signed-off-by line.
> 
> Thanks!
> 
> On Wed, Sep 23, 2015 at 04:12:05PM +0200, Wolfgang Bumiller wrote:
> > As I mentioned in an earlier email (sorry it took a little longer as
> > we were still going through some options), we'd like to have the
> > possibility to deal with mountpoints after the container has stopped.
> > 
> > This series adds an `lxc.hook.stop` option, and passes handles to the
> > container namespaces to it. The hook is executed between the STOPPING
> > and STOPPED states, which means the container processes are already
> > gone, and to be able to access the mount namespace the preserve_ns
> > function is used which opens the ns files. (They're closed in
> > lxc_fini.)
> > 
> > As for how they're passed to the hook: you might have a different
> > idea about how to do that better. Currently they're passed as paths to
> > the '/proc/*/fd' entry prefixed with their 'proc_name' (from ns_info).
> > (I did think about just passing the numbers and disabling CLOEXEC, but
> > that would mean stop-hooks are always forced to deal with them, even
> > if someone doesn't care, otherwise they might be leaked to other
> > processes.)
> > Environment variables would also be a possibility.
> > But this way the hook has the option to enter the namespaces by
> > opening the filedescriptors of the lxc process itself.
> > 
> > If you want the patches squashed/changed/... just say so. If you
> > decide they're worth adding I'll happily supplement them with patches
> > for the documentation (lxc.hook.stop man page entry).
> > 
> > Here's again our use-case summarized: When migrating a container from
> > one node to another, there's a chance that they might be accessing a
> > network filesystem (eg we can have the root disk as an image file on
> > an NFS share), and we need to know that the filesystems were unmounted
> > successfully before starting the container on another node (as NFS may
> > still be syncing, or worse: hanging due to a lost connection, which we
> > want to catch and prevent the container from starting with a broken
> > filesystem without user-intervention).
> > 
> > Wolfgang Bumiller (5):
> >   start.c:preserve_ns: added pid parameter
> >   preserve container namespace
> >   added stop-hook entries
> >   run stop hook between STOPPING and STOPPED states
> >   pass namespace handles to the stop hook
> > 
> >  src/lxc/conf.c    |  4 +++-
> >  src/lxc/conf.h    |  2 +-
> >  src/lxc/confile.c |  3 +++
> >  src/lxc/start.c   | 44 ++++++++++++++++++++++++++++++++++++++++----
> >  src/lxc/start.h   |  1 +
> >  5 files changed, 48 insertions(+), 6 deletions(-)
> > 
> > -- 
> > 2.1.4
> > 
> > 
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
> 
> -- 
> Stéphane Graber
> Ubuntu developer
> http://www.ubuntu.com



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