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

[Andrew Vagin]

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...

> +	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?

> +
> +	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
>