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

[Oren Laadan]

the continuation of the thread.

On Wed, Nov 19, 2014 at 9:37 AM, Serge Hallyn <serge.hallyn at ubuntu.com>
wrote:

> 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
>
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