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

[Abin Shahab]

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>
> > ---
> >  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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