mount: Handle deleted bindmounts

To handle deleted bindmounts we simply create
the former directory bindmount lived at, mount
the target and remove the directory back.

For this sake we add @deleted entry into the image.
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>

include/mount.h

@@ -58,6 +58,7 @@ struct mount_info {
 	};
 	bool			need_plugin;
 	bool			is_ns_root;
+	bool			deleted;
 	struct mount_info	*next;
 	struct ns_id		*nsid;
 

mount.c

@@ -1590,6 +1590,10 @@ static int dump_one_mountpoint(struct mount_info *pm, struct cr_img *img)
 		me.has_with_plugin = true;
 		me.with_plugin = true;
 	}
+	if (pm->deleted) {
+		me.has_deleted	= true;
+		me.deleted	= true;
+	}
 
 	if (pm->internal_sharing) {
 		me.has_internal_sharing = true;
@@ -1990,11 +1994,25 @@ static int do_bind_mount(struct mount_info *mi)
 		root = rpath;
 do_bind:
 		pr_info("\tBind %s to %s\n", root, mi->mountpoint);
-		if (mount(root, mi->mountpoint, NULL,
-					MS_BIND, NULL) < 0) {
+
+		if (unlikely(mi->deleted)) {
+			if (mkdir(root, 0700)) {
+				pr_perror("Can't re-create deleted %s\n", root);
+				return -1;
+			}
+		}
+
+		if (mount(root, mi->mountpoint, NULL, MS_BIND, NULL) < 0) {
 			pr_perror("Can't mount at %s", mi->mountpoint);
 			return -1;
 		}
+
+		if (unlikely(mi->deleted)) {
+			if (rmdir(root)) {
+				pr_perror("Can't remove deleted %s\n", root);
+				return -1;
+			}
+		}
 	} else {
 		if (restore_ext_mount(mi))
 			return -1;
@@ -2308,6 +2326,7 @@ static int collect_mnt_from_image(struct mount_info **pms, struct ns_id *nsid)
 		pm->shared_id		= me->shared_id;
 		pm->master_id		= me->master_id;
 		pm->need_plugin		= me->with_plugin;
+		pm->deleted		= me->deleted;
 		pm->is_ns_root		= is_root(me->mountpoint);
 
 		pr_debug("\t\tGetting source for %d\n", pm->mnt_id);

proc_parse.c

@@ -29,6 +29,7 @@
 #include "sysfs_parse.h"
 #include "seccomp.h"
 #include "namespaces.h"
+#include "files-reg.h"
 
 #include "protobuf.h"
 #include "protobuf/fdinfo.pb-c.h"
@@ -1008,6 +1009,7 @@ replace:
 
 static int parse_mountinfo_ent(char *str, struct mount_info *new, char **fsname)
 {
+	struct fd_link root_link;
 	unsigned int kmaj, kmin;
 	int ret, n;
 	char *sub, *opt = NULL;
@@ -1027,6 +1029,13 @@ static int parse_mountinfo_ent(char *str, struct mount_info *new, char **fsname)
 	cure_path(new->mountpoint);
 	cure_path(new->root);
 
+	root_link.len = strlen(new->root);
+	strcpy(root_link.name, new->root);
+	if (strip_deleted(&root_link)) {
+		strcpy(new->root, root_link.name);
+		new->deleted = true;
+	}
+
 	new->mountpoint = xrealloc(new->mountpoint, strlen(new->mountpoint) + 1);
 	if (!new->mountpoint)
 		goto err;

protobuf/mnt.proto

@@ -41,4 +41,6 @@ message mnt_entry {
 
 	optional string		fsname			= 14;
 	optional bool		internal_sharing	= 15;
+
+	optional bool		deleted			= 16;
 }