[CRIU] [PATCH 5/9] mounts: handle bind-mounts

[Andrey Vagin]

A non-root mount is bind-mounted to a proper root mount.

Non-root mount without root mount is not supported yet

Signed-off-by: Andrey Vagin <avagin at openvz.org>
---
 include/proc_parse.h |  2 ++
 mount.c              | 75 +++++++++++++++++++++++++++++++++++++---------------
 2 files changed, 55 insertions(+), 22 deletions(-)

diff --git a/include/proc_parse.h b/include/proc_parse.h
index 99255c4..1325424 100644
--- a/include/proc_parse.h
+++ b/include/proc_parse.h
@@ -114,9 +114,11 @@ struct mount_info {
 
 	/* tree linkage */
 	struct mount_info *parent;
+	struct mount_info *bind;
 	struct list_head children;
 	struct list_head siblings;
 
+	struct list_head mnt_bind;
 	struct list_head mnt_share;	/* circular list of shared mounts */
 	struct list_head mnt_slave_list;/* list of slave mounts */
 	struct list_head mnt_slave;	/* slave list entry */
diff --git a/mount.c b/mount.c
index 640cd12..31b1f3c 100644
--- a/mount.c
+++ b/mount.c
@@ -77,6 +77,16 @@ struct mount_info *lookup_mnt_sdev(unsigned int s_dev)
 	return NULL;
 }
 
+/* two bind-mounts are reported as equal if bind is true */
+static bool mntcmp(struct mount_info* mi, struct mount_info *c, bool bind)
+{
+	return (mi->s_dev == c->s_dev &&
+		(bind || !strcmp(c->root, mi->root)) &&
+		!strcmp(c->source, mi->source) &&
+		!strcmp(c->options, mi->options) &&
+		c->fstype == mi->fstype);
+}
+
 static struct mount_info *mnt_build_ids_tree(struct mount_info *list)
 {
 	struct mount_info *m, *root = NULL;
@@ -178,6 +188,21 @@ static void mnt_tree_show(struct mount_info *tree, int off)
 	pr_info("%*s<--\n", off, "");
 }
 
+static inline int is_root(char *p)
+{
+	return p[0] == '/' && p[1] == '\0';
+}
+
+static inline int is_root_mount(struct mount_info *mi)
+{
+	return is_root(mi->mountpoint);
+}
+
+static inline int fsroot_mounted(struct mount_info *mi)
+{
+	return is_root(mi->root);
+}
+
 static int collect_shared(struct mount_info *info)
 {
 	struct mount_info *m, *t;
@@ -197,6 +222,7 @@ static int collect_shared(struct mount_info *info)
 		for (t = info; t && (share || master); t = t->next) {
 			if (t == m)
 				continue;
+
 			if (master && t->shared_id == m->master_id) {
 				pr_debug("The mount %d is slave for %d\n", m->mnt_id, t->mnt_id);
 				list_add(&m->mnt_slave, &t->mnt_slave_list);
@@ -211,13 +237,20 @@ static int collect_shared(struct mount_info *info)
 				list_add(&m->mnt_share, &t->mnt_share);
 			}
 		}
-		if (!master)
-			continue;
 
-		pr_err("Mount %d (master_id: %d shared_id: %d) "
-		       "has unreachable sharing\n", m->mnt_id,
-			m->master_id, m->shared_id);
-		return -1;
+		if (master) {
+			pr_err("Mount %d (master_id: %d shared_id: %d) "
+			       "has unreachable sharing\n", m->mnt_id,
+				m->master_id, m->shared_id);
+			return -1;
+		}
+
+		/* Search bind-mounts */
+		if (list_empty(&m->mnt_bind))
+			for (t = m->next; t; t = t->next) {
+				if (mntcmp(m, t, true))
+					list_add(&t->mnt_bind, &m->mnt_bind);
+			}
 	}
 
 	return 0;
@@ -432,16 +465,6 @@ static struct fstype *decode_fstype(u32 fst)
 	return &fstypes[fst];
 }
 
-static inline int is_root(char *p)
-{
-	return p[0] == '/' && p[1] == '\0';
-}
-
-static inline int is_root_mount(struct mount_info *mi)
-{
-	return is_root(mi->mountpoint);
-}
-
 static int dump_one_mountpoint(struct mount_info *pm, int fd)
 {
 	MntEntry me = MNT_ENTRY__INIT;
@@ -565,6 +588,7 @@ static int do_new_mount(struct mount_info *mi)
 {
 	char *src;
 	struct fstype *tp = mi->fstype;
+	struct mount_info *t;
 
 	src = resolve_source(mi);
 	if (!src)
@@ -579,18 +603,24 @@ static int do_new_mount(struct mount_info *mi)
 	if (tp->restore && tp->restore(mi))
 		return -1;
 
+	list_for_each_entry(t, &mi->mnt_bind, mnt_bind)
+		t->bind = mi;
+
 	return 0;
 }
 
 static int do_bind_mount(struct mount_info *mi)
 {
-	pr_err("No bind mounts at %s\n", mi->mountpoint);
-	return -1;
-}
+	char rpath[PATH_MAX];
 
-static inline int fsroot_mounted(struct mount_info *mi)
-{
-	return is_root(mi->root);
+	snprintf(rpath, sizeof(rpath), "%s%s", mi->bind->mountpoint, mi->root);
+
+	if (mount(rpath, mi->mountpoint, NULL,
+				MS_BIND, NULL) < 0) {
+		pr_perror("Can't mount at %s", mi->mountpoint);
+		return -1;
+	}
+	return 0;
 }
 
 static int do_mount_one(struct mount_info *mi)
@@ -704,6 +734,7 @@ struct mount_info *mnt_entry_alloc()
 		INIT_LIST_HEAD(&new->siblings);
 		INIT_LIST_HEAD(&new->mnt_slave_list);
 		INIT_LIST_HEAD(&new->mnt_share);
+		INIT_LIST_HEAD(&new->mnt_bind);
 		new->mnt_master = NULL;
 	}
 	return new;
-- 
1.8.3.1