[lxc-devel] [PATCH 1/1] lxc-start-ephemeral: handle the overlayfs workdir option (v2)

[Serge Hallyn]

Quoting KATOH Yasufumi (karma at jazz.email.ne.jp):
> Hi,
> 
> I tested on kernel 3.18.1 with your patch. It works fine, but there is
> one problem.
> 
> >>> On Tue, 13 Jan 2015 00:08:37 +0000
>     in message   "[lxc-devel] [PATCH 1/1] lxc-start-ephemeral: handle the overlayfs workdir option (v2)"
>                   Serge Hallyn-san wrote:
> 
> > We fixed this some time ago for basic lxc-start, but never did
> > lxc-start-ephemeral.
> 
> > Since the lxc-start patches were pushed, Miklos has given us a
> > way to detect whether we need the workdir= option.  So the
> > bdev.c code could be simplified to check for "overlay\n" in
> > /proc/filesystems just as lxc-start-ephemeral does.  This
> > patch doesn't do that.
> 
> 
> 
> > Changelog (v2):
> > 	1. use 'overlay' fstype for new overlay upstream module
> > 	2. avoid using unneeded readlines().
> 
> > Signed-off-by: Serge Hallyn <serge.hallyn at ubuntu.com>
> > ---
> >  src/lxc/lxc-start-ephemeral.in | 25 ++++++++++++++++++++++++-
> >  1 file changed, 24 insertions(+), 1 deletion(-)
> 
> > diff --git a/src/lxc/lxc-start-ephemeral.in b/src/lxc/lxc-start-ephemeral.in
> > index c999e74..36e2579 100644
> > --- a/src/lxc/lxc-start-ephemeral.in
> > +++ b/src/lxc/lxc-start-ephemeral.in
> > @@ -219,6 +219,14 @@ for entry in args.cdir:
> >          dst_path = "%s/rootfs/%s" % (dest_path, src_path)
> >          overlay_dirs += [(src_path, dst_path)]
>  
> > +# do we have the new overlay fs which requires workdir, or the older
> > +# overlayfs which does not?
> > +have_new_overlay = False
> > +with open("/proc/filesystems", "r") as fd:
> > +    for line in fd:
> > +        if line == "nodev\toverlay\n":
> > +            have_new_overlay = True
> 
> When the overlayfs is module, and the module is not loaded at this
> moment, "have_new_overlay" is False and the mount will fail.
> 
> We need to load the overlayfs module before the check.

Yeah I thought of that when I started, then I guess ended up
ignoring it.  What would be the cleanest way to do this in
python?  Stéphane?

> > +
> >  # Generate pre-mount script
> >  with open(os.path.join(dest_path, "pre-mount"), "w+") as fd:
> >      os.fchmod(fd.fileno(), 0o755)
> > @@ -231,16 +239,31 @@ LXC_NAME="%s"
> >      count = 0
> >      for entry in overlay_dirs:
> >          target = "%s/delta%s" % (dest_path, count)
> > +        workdir = "%s/work%s" % (dest_path, count)
> >          fd.write("mkdir -p %s %s\n" % (target, entry[1]))
> > +        if have_new_overlay:
> > +            fd.write("mkdir -p %s\n" % workdir)
>  
> >          if args.storage_type == "tmpfs":
> >              fd.write("mount -n -t tmpfs -o mode=0755 none %s\n" % (target))
> > +            if have_new_overlay:
> > +                fd.write("mount -n -t tmpfs -o mode=0755 none %s\n" % (workdir))
>  
> >          fd.write("getfacl -a %s | setfacl --set-file=- %s || true\n" % (entry[0], target))
> >          fd.write("getfacl -a %s | setfacl --set-file=- %s || true\n" % (entry[0], entry[1]))
> > +        if have_new_overlay:
> > +            fd.write("getfacl -a %s | setfacl --set-file=- %s || true\n" % (entry[0], workdir))
>  
> >          if args.union_type == "overlayfs":
> > -            fd.write("mount -n -t overlayfs"
> > +            if have_new_overlay:
> > +                fd.write("mount -n -t overlay"
> > +                     " -oupperdir=%s,lowerdir=%s,workdir=%s none %s\n" % (
> > +                         target,
> > +                         entry[0],
> > +                         workdir,
> > +                         entry[1]))
> > +            else:
> > +                fd.write("mount -n -t overlayfs"
> >                       " -oupperdir=%s,lowerdir=%s none %s\n" % (
> >                           target,
> >                           entry[0],
> > -- 
> > 2.1.0
> 
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