[CRIU] [PATCH 3/5] mounts: make pivot_root after restoring mount points

[Pavel Emelyanov]

On 02/21/2014 05:51 PM, Andrey Vagin wrote:
> In this case we can use tar for restoring tmpfs, we don't need to
> premount external mounts, etc

This comment is bad.
And, the link on bug is missing.

> Signed-off-by: Andrey Vagin <avagin at openvz.org>
> ---
>  mount.c | 109 +++++++++++-----------------------------------------------------
>  1 file changed, 19 insertions(+), 90 deletions(-)
> 
> diff --git a/mount.c b/mount.c
> index d315e4c..0aa7238 100644
> --- a/mount.c
> +++ b/mount.c
> @@ -1080,30 +1080,6 @@ static int restore_ext_mount(struct mount_info *mi)
>  {
>  	int ret;
>  
> -	if (opts.root) {
> -		char temp[32];
> -
> -		/*
> -		 * The mount was created in premount_one, just move it
> -		 * in the desired place, now it's available.
> -		 */
> -		sprintf(temp, "/crt-premount.%d", mi->mnt_id);
> -		pr_debug("Moving mountpoint %s -> %s\n", temp, mi->mountpoint);
> -		if (mount(temp, mi->mountpoint, NULL, MS_MOVE, NULL) < 0) {
> -			pr_perror("Can't move mount %s", mi->mountpoint);
> -			return -1;
> -		}
> -
> -		if (mi->is_file)
> -			ret = unlink(temp);
> -		else
> -			ret = rmdir(temp);
> -		if (ret < 0)
> -			pr_perror("Can't remove temp dir");
> -
> -		return 0;
> -	}
> -
>  	pr_debug("Restoring external bind mount %s\n", mi->mountpoint);
>  	ret = cr_plugin_restore_ext_mount(mi->mnt_id, mi->mountpoint, "/", NULL);
>  	if (ret)
> @@ -1221,52 +1197,7 @@ static int clean_mnt_ns(void)
>  	return mnt_tree_for_each_reverse(mntinfo_tree, do_umount_one);
>  }
>  
> -static int premount_one(struct mount_info *mi, char *old_root)
> -{
> -	int ret;
> -	char temp[32];
> -
> -	if (!mi->need_plugin)
> -		return 0;
> -
> -	/*
> -	 * We can't mount the source to proper target yet (the
> -	 * new tree is not yet ready. Instead, we ask plugin to
> -	 * mount it on a temporary path, later (opts.root branch
> -	 * of the restore_ext_mount) we will move the mountpoint
> -	 * in the proper place.
> -	 */
> -	sprintf(temp, "/crt-premount.%d", mi->mnt_id);
> -	pr_debug("Pre external %s -> %s\n", mi->mountpoint, temp);
> -
> -	/*
> -	 * Don't create anything on that path here -- the plugin
> -	 * might want to bind mount a file OR a directory and since
> -	 * those cannot be binded to each other, the plugin itself
> -	 * should create the target.
> -	 *
> -	 * BTW, the mi->is_file is about the same -- after we move
> -	 * the mount in place, we will either rmdir or unlink this
> -	 * temporary location.
> -	 */
> -	ret = cr_plugin_restore_ext_mount(mi->mnt_id, temp, old_root, &mi->is_file);
> -	if (ret)
> -		pr_perror("Can't premount ext mount (%d)", ret);
> -	return ret;
> -}
> -
> -static int premount_external(struct mount_info *mis, char *old_root)
> -{
> -	while (mis != 0) {
> -		if (premount_one(mis, old_root))
> -			return -1;
> -		mis = mis->next;
> -	}
> -
> -	return 0;
> -}
> -
> -static int cr_pivot_root(struct mount_info *mis)
> +static int cr_pivot_root(void)
>  {
>  	char put_root[] = "crtools-put-root.XXXXXX";
>  
> @@ -1284,14 +1215,6 @@ static int cr_pivot_root(struct mount_info *mis)
>  		return -1;
>  	}
>  
> -	/*
> -	 * Before we get rid of the old FS view, call plugins
> -	 * to let them bind-mount whatever is necessary into
> -	 * the new tree (see comment in premount_one.
> -	 */
> -	if (premount_external(mis, put_root))
> -		return -1;
> -
>  	if (umount2(put_root, MNT_DETACH)) {
>  		pr_perror("Can't umount %s", put_root);
>  		return -1;
> @@ -1457,12 +1380,6 @@ int prepare_mnt_ns(int ns_pid)
>  	if (!mis)
>  		goto out;
>  
> -	/*
> -	 * The new mount namespace is filled with the mountpoint
> -	 * clones from the original one. We have to umount them
> -	 * prior to recreating new ones.
> -	 */
> -
>  	if (mount("none", "/", "none", MS_REC|MS_PRIVATE, NULL)) {
>  		pr_perror("Can't remount root with MS_PRIVATE");
>  		return -1;
> @@ -1473,15 +1390,27 @@ int prepare_mnt_ns(int ns_pid)
>  		return -1;
>  	}
>  
> -	if (opts.root)
> -		ret = cr_pivot_root(mis);
> -	else
> -		ret = clean_mnt_ns();
> +	/*
> +	 * The new mount namespace is filled with the mountpoint
> +	 * clones from the original one. We have to umount them
> +	 * prior to recreating new ones.
> +	 */
> +	if (!opts.root && clean_mnt_ns())
> +		return -1;
>  
>  	free_mounts();
>  
> -	if (!ret)
> -		ret = populate_mnt_ns(ns_pid, mis);
> +	if (chdir(opts.root ? : "/")) {
> +		pr_perror("chdir(%s) failed", opts.root);
> +		return -1;
> +	}
> +
> +	ret = populate_mnt_ns(ns_pid, mis);
> +	if (ret)
> +		goto out;
> +
> +	if (opts.root)
> +		ret = cr_pivot_root();
>  out:
>  	return ret;
>  }
>