[lxc-devel] [PATCH] Remounts bind mounts if read-only flag is provided

[Serge Hallyn]

Quoting Abin Shahab (ashahab at altiscale.com):
> Yes. It's documented in the mount man page.
> Thanks for looking at the patch.
> On Nov 18, 2014 1:04 PM, "Serge Hallyn" <serge.hallyn at ubuntu.com> wrote:
> 
> > Quoting Abin Shahab (ashahab at altiscale.com):
> > > Bind mounts do not honor filesystem mount options. This change will
> > remount filesystems that are bind mounted if there are changes to
> > filesystem mount options, specifically if the mount is readonly.
> >
> > hi,
> >
> > Just to make sure I understand what you're saying,
> >
> > 'mount --bind -o ro /a /b' (when done through mount(2)) will not
> > actually make /b readonly, so we need to do a remount in that case
> > to get the -o ro to take effect at the vfsmount instead of the sb.
> > Is that right?
> >
> > > Signed-off-by: Abin Shahab <ashahab at altiscale.com>

Thanks, great catch.

Acked-by: Serge E. Hallyn <serge.hallyn at ubuntu.com>

Stéphane, this one is pretty important, please do get this into stable
as well.

> > > ---
> > >  src/lxc/conf.c | 8 +++++---
> > >  1 file changed, 5 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/src/lxc/conf.c b/src/lxc/conf.c
> > > index 5938c3e..a3779de 100644
> > > --- a/src/lxc/conf.c
> > > +++ b/src/lxc/conf.c
> > > @@ -1921,10 +1921,12 @@ static int mount_entry(const char *fsname, const
> > char *target,
> > >       if ((mountflags & MS_REMOUNT) || (mountflags & MS_BIND)) {
> > >               DEBUG("remounting %s on %s to respect bind or remount
> > options",
> > >                     fsname ? fsname : "(none)", target ? target :
> > "(none)");
> > > -
> > > +             unsigned long rqd_flags = 0;
> > > +             if (mountflags & MS_RDONLY)
> > > +                     rqd_flags |= MS_RDONLY;
> > >  #ifdef HAVE_STATVFS
> > >               if (statvfs(fsname, &sb) == 0) {
> > > -                     unsigned long required_flags = 0;
> > > +                     unsigned long required_flags = rqd_flags;
> > >                       if (sb.f_flag & MS_NOSUID)
> > >                               required_flags |= MS_NOSUID;
> > >                       if (sb.f_flag & MS_NODEV)
> > > @@ -1940,7 +1942,7 @@ static int mount_entry(const char *fsname, const
> > char *target,
> > >                        * mountflags, then skip the remount
> > >                        */
> > >                       if (!(mountflags & MS_REMOUNT)) {
> > > -                             if (!(required_flags & ~mountflags)) {
> > > +                             if (!(required_flags & ~mountflags) &&
> > rqd_flags == 0) {
> > >                                       DEBUG("mountflags already was %lu,
> > skipping remount",
> > >                                               mountflags);
> > >                                       goto skipremount;
> > > --
> > > 2.1.0
> > >
> > > _______________________________________________
> > > lxc-devel mailing list
> > > lxc-devel at lists.linuxcontainers.org
> > > http://lists.linuxcontainers.org/listinfo/lxc-devel
> > _______________________________________________
> > lxc-devel mailing list
> > lxc-devel at lists.linuxcontainers.org
> > http://lists.linuxcontainers.org/listinfo/lxc-devel
> >

> _______________________________________________
> lxc-devel mailing list
> lxc-devel at lists.linuxcontainers.org
> http://lists.linuxcontainers.org/listinfo/lxc-devel