[CRIU] [PATCH 4/5] mount: migrate bindmounts of external mounts

[Andrew Vagin]

On Thu, Mar 02, 2017 at 09:26:40AM +0300, Pavel Tikhomirov wrote:
> ----Пользователь Andrew Vagin написал ----
> 
> > On Wed, Mar 01, 2017 at 04:17:44PM +0300, Pavel Tikhomirov wrote:
> > > If container has external bindmount given to criu through
> > > --ext-mount-map option by admin, container user can bindmount
> > > subdirs of these external bindmount to somewhere else inside
> > > container creating secondary external binmouns. Criu we will
> > > fail to restore them as having unreachable sharing. But we can
> > > restore secondary external bindmounts bindmounting them from
> > > primary external bindmount.
> > >
> > > https://jira.sw.ru/browse/PSBM-46753
> > > Signed-off-by: Pavel Tikhomirov <ptikhomirov at virtuozzo.com>
> > > ---
> > >  criu/mount.c | 41 ++++++++++++++++++++++++++++++++++++-----
> > >  1 file changed, 36 insertions(+), 5 deletions(-)
> > >
> > > diff --git a/criu/mount.c b/criu/mount.c
> > > index bd2497b..22a9c13 100644
> > > --- a/criu/mount.c
> > > +++ b/criu/mount.c
> > > @@ -640,6 +640,35 @@ static bool does_mnt_overmount(struct mount_info *m)
> > >  return false;
> > >  }
> > > 
> > > +/*
> > > + * Say we are external_bind if we are external or we
> > > + * will be bind from external, we set bind in propagate_mount
> > > + * and propagate_siblings
> > > + */
> > > +
> > > +static struct mount_info *external_bind(struct mount_info *m) {
> >
> > Can we call this function as mnt_is_external? A return value isn't
> > used...
> 
> Yes, will do boolean ret and rename.
> 
> >
> > > + struct mount_info *t;
> > > +
> > > + if (m->external)
> > > + return m;
> > > +
> > > + if (!list_empty(&m->mnt_share))
> > > + list_for_each_entry(t, &m->mnt_share, mnt_share)
> > > + if (t->external)
> > > + return t;
> > > +
> > > + if (m->mnt_master)
> > > + return external_bind(m->mnt_master);
> >
> > We do we need to check mnt_master here?
> 
> Imagine we have non-root external mount, it's shared bind-mount and latter's
> slave bind-mount, so that criu thinks that mnt_master of the third is the
> second. In that case we will first restore external, next restore the second
> (shared) as external's bind and last the third(slave) as a bind of shared
> (through mount propagation). We just need to allow third mount, and to find out
> that it is allowed we need to go through all masters and search their shares.
> 

Will the test fail if we remove this check? If the answer is no, could
you extand the test? Thanks.

> >
> > > +
> > > + if (m->master_id > 0)
> > > + return NULL;
> > > + if (!list_empty(&m->mnt_bind))
> > > + list_for_each_entry(t, &m->mnt_bind, mnt_bind)
> > > + if (issubpath(m->root, t->root) && t->external)
> > > + return t;
> > > + return NULL;
> > > +}
> > > +
> > >  static int validate_mounts(struct mount_info *info, bool for_dump)
> > >  {
> > >  struct mount_info *m, *t;
> > > @@ -652,7 +681,7 @@ static int validate_mounts(struct mount_info *info,
> bool for_dump)
> > >  if (m->shared_id && validate_shared(m))
> > >  return -1;
> > > 
> > > - if (m->external)
> > > + if (external_bind(m))
> > >  goto skip_fstype;
> > > 
> > >  /*
> > > @@ -908,9 +937,9 @@ static int resolve_shared_mounts(struct mount_info
> *info, int root_master_id)
> > > 
> > >  /*
> > >  * If we haven't already determined this mount is external,
> > > - * then we don't know where it came from.
> > > + * or bind of external, then we don't know where it came from.
> > >  */
> > > - if (need_master && m->parent && !m->external) {
> > > + if (need_master && m->parent && !external_bind(m)) {
> > >  pr_err("Mount %d %s (master_id: %d shared_id: %d) "
> > >         "has unreachable sharing. Try --enable-external-masters.\n", m->
> mnt_id,
> > >  m->mountpoint, m->master_id, m->shared_id);
> > > @@ -1222,7 +1251,7 @@ static int dump_one_fs(struct mount_info *mi)
> > >  struct mount_info *t;
> > >  bool first = true;
> > > 
> > > - if (mi->is_ns_root || mi->need_plugin || mi->external || !mi->fstype->
> dump)
> > > + if (mi->is_ns_root || mi->need_plugin || external_bind(mi) || !mi->
> fstype->dump)
> > >  return 0;
> > > 
> > >  /* mnt_bind is a cycled list, so list_for_each can't be used here. */
> > > @@ -1634,7 +1663,7 @@ static int propagate_mount(struct mount_info *mi)
> > >  * FIXME Currently non-root mounts can be restored
> > >  * only if a proper root mount exists
> > >  */
> > > - if (fsroot_mounted(mi) || mi->parent == root_yard_mp) {
> > > + if (fsroot_mounted(mi) || mi->parent == root_yard_mp || mi->external) {
> > >  list_for_each_entry(t, &mi->mnt_bind, mnt_bind) {
> > >  if (t->mounted)
> > >  continue;
> > > @@ -1642,6 +1671,8 @@ static int propagate_mount(struct mount_info *mi)
> > >  continue;
> > >  if (t->master_id > 0)
> > >  continue;
> > > + if (!issubpath(t->root, mi->root))
> > > + continue;
> > >  t->bind = mi;
> > >  t->s_dev_rt = mi->s_dev_rt;
> > >  }
> > > --
> > > 2.9.3
> > >