[CRIU] [PATCH] mount: rework perparation for pivot_root

[Andrew Vagin]

On Fri, Aug 08, 2014 at 09:34:39AM -0500, Tycho Andersen wrote:
> Hi Andrey,
> 
> On Fri, Aug 08, 2014 at 04:18:10PM +0400, Andrey Vagin wrote:
> > We can't bind-mount the required root into itself instead of
> > resolving a parent mount.
> > 
> > This patch is required to support userns, because if we want to make
> > pivot_root, the parent mount can't be locked. When we create userns
> > and mntns, all inherited mounts are marked as locked.
> > 
> > Cc: Tycho Andersen <tycho.andersen at canonical.com>
> > Signed-off-by: Andrey Vagin <avagin at openvz.org>
> > ---
> >  mount.c | 48 +++++++++++++++++++++---------------------------
> >  1 file changed, 21 insertions(+), 27 deletions(-)
> > 
> > diff --git a/mount.c b/mount.c
> > index 3287282..15902c7 100644
> > --- a/mount.c
> > +++ b/mount.c
> > @@ -1910,20 +1910,13 @@ int fini_mnt_ns(void)
> >  int prepare_mnt_ns(void)
> >  {
> >  	int ret = -1;
> > -	struct mount_info *mis, *old;
> > -	struct ns_id ns = { .pid = PROC_SELF, .nd = &mnt_ns_desc };
> > +	struct mount_info *mis;
> >  
> >  	if (!(root_ns_mask & CLONE_NEWNS))
> >  		return rst_collect_local_mntns();
> >  
> >  	pr_info("Restoring mount namespace\n");
> >  
> > -	old = collect_mntinfo(&ns);
> > -	if (old == NULL)
> > -		return -1;
> > -
> > -	close_proc();
> > -
> >  	mis = read_mnt_ns_img();
> >  	if (!mis)
> >  		goto out;
> > @@ -1939,36 +1932,37 @@ int prepare_mnt_ns(void)
> >  	 * prior to recreating new ones.
> >  	 */
> >  	if (!opts.root) {
> > -		if (clean_mnt_ns(ns.mnt.mntinfo_tree))
> > +		struct ns_id ns = { .pid = PROC_SELF, .nd = &mnt_ns_desc };
> > +		struct mount_info *old;
> > +		int err;
> > +
> > +		old = collect_mntinfo(&ns);
> > +		if (old == NULL)
> >  			return -1;
> > -	} else {
> > -		struct mount_info *mi;
> >  
> > -		/* moving a mount residing under a shared mount is invalid. */
> > -		mi = mount_resolve_path(ns.mnt.mntinfo_tree, opts.root);
> > -		if (mi == NULL) {
> > -			pr_err("Unable to find mount point for %s\n", opts.root);
> > +		close_proc();
> > +
> > +		err = clean_mnt_ns(ns.mnt.mntinfo_tree);
> > +		free_mntinfo(old);
> > +		if (err)
> >  			return -1;
> > -		}
> > -		if (mi->parent == NULL) {
> > -			pr_err("New root and old root are the same\n");
> > +	} else {
> > +		close_proc();
> > +
> > +		if (mount("none", opts.root, "none", MS_SLAVE, NULL)) {
> > +			pr_perror("Can't remount the parent of the new root with MS_SLAVE");
> >  			return -1;
> >  		}
> 
> I get this error:
> 
> Error (mount.c:1953): Can't remount the parent of the new root with MS_SLAVE: Invalid argument
> 
> when I try with this patch.

Is the opts.root path a mount point?

Could you try the attached patcn?

> 
> Tycho
> 
> > -
> > -		/* Our root is mounted over the parent (in the same directory) */
> > -		if (!strcmp(mi->parent->mountpoint, mi->mountpoint)) {
> > -			pr_err("The parent of the new root is unreachable\n");
> > +		if (mount(opts.root, opts.root, NULL, MS_BIND, NULL)) {
> > +			pr_perror("Unable to bind-mount %s", opts.root);
> >  			return -1;
> >  		}
> > -
> > -		if (mount("none", mi->parent->mountpoint + 1, "none", MS_SLAVE, NULL)) {
> > -			pr_perror("Can't remount the parent of the new root with MS_SLAVE");
> > +		if (chdir(opts.root)) {
> > +			pr_perror("chdir(%s) failed", opts.root);
> >  			return -1;
> >  		}
> >  	}
> >  
> > -	free_mntinfo(old);
> > -
> >  	ret = populate_mnt_ns(mis);
> >  	if (ret)
> >  		goto out;
> > -- 
> > 1.9.3
> >