ANDROID: mnt: Add filesystem private data to mount points

This starts to add private data associated directly
to mount points. The intent is to give filesystems
a sense of where they have come from, as a means of
letting a filesystem take different actions based on
this information.

Bug: 62094374
Bug: 120446149
Change-Id: Ie769d7b3bb2f5972afe05c1bf16cf88c91647ab2
Signed-off-by: Daniel Rosenberg <drosen@google.com>
[astrachan: Folded 89a54ed3bf68 ("ANDROID: mnt: Fix next_descendent")
            into this patch]
Signed-off-by: Alistair Strachan <astrachan@google.com>

fs/namespace.c

@@ -200,6 +200,7 @@ static struct mount *alloc_vfsmnt(const char *name)
 		mnt->mnt_count = 1;
 		mnt->mnt_writers = 0;
 #endif
+		mnt->mnt.data = NULL;
 
 		INIT_HLIST_NODE(&mnt->mnt_hash);
 		INIT_LIST_HEAD(&mnt->mnt_child);
@@ -552,6 +553,7 @@ int sb_prepare_remount_readonly(struct super_block *sb)
 
 static void free_vfsmnt(struct mount *mnt)
 {
+	kfree(mnt->mnt.data);
 	kfree_const(mnt->mnt_devname);
 #ifdef CONFIG_SMP
 	free_percpu(mnt->mnt_pcp);
@@ -955,6 +957,14 @@ vfs_kern_mount(struct file_system_type *type, int flags, const char *name, void
 	if (!mnt)
 		return ERR_PTR(-ENOMEM);
 
+	if (type->alloc_mnt_data) {
+		mnt->mnt.data = type->alloc_mnt_data();
+		if (!mnt->mnt.data) {
+			mnt_free_id(mnt);
+			free_vfsmnt(mnt);
+			return ERR_PTR(-ENOMEM);
+		}
+	}
 	if (flags & SB_KERNMOUNT)
 		mnt->mnt.mnt_flags = MNT_INTERNAL;
 
@@ -1002,6 +1012,14 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,
 	if (!mnt)
 		return ERR_PTR(-ENOMEM);
 
+	if (sb->s_op->clone_mnt_data) {
+		mnt->mnt.data = sb->s_op->clone_mnt_data(old->mnt.data);
+		if (!mnt->mnt.data) {
+			err = -ENOMEM;
+			goto out_free;
+		}
+	}
+
 	if (flag & (CL_SLAVE | CL_PRIVATE | CL_SHARED_TO_SLAVE))
 		mnt->mnt_group_id = 0; /* not a peer of original */
 	else
@@ -2286,8 +2304,14 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 		err = change_mount_flags(path->mnt, ms_flags);
 	else if (!ns_capable(sb->s_user_ns, CAP_SYS_ADMIN))
 		err = -EPERM;
-	else
+	else {
 		err = do_remount_sb(sb, sb_flags, data, 0);
+		namespace_lock();
+		lock_mount_hash();
+		propagate_remount(mnt);
+		unlock_mount_hash();
+		namespace_unlock();
+	}
 	if (!err) {
 		lock_mount_hash();
 		mnt_flags |= mnt->mnt.mnt_flags & ~MNT_USER_SETTABLE_MASK;

fs/pnode.c

@@ -607,3 +607,37 @@ int propagate_umount(struct list_head *list)
 
 	return 0;
 }
+
+/*
+ *  Iterates over all slaves, and slaves of slaves.
+ */
+static struct mount *next_descendent(struct mount *root, struct mount *cur)
+{
+	if (!IS_MNT_NEW(cur) && !list_empty(&cur->mnt_slave_list))
+		return first_slave(cur);
+	do {
+		struct mount *master = cur->mnt_master;
+
+		if (!master || cur->mnt_slave.next != &master->mnt_slave_list) {
+			struct mount *next = next_slave(cur);
+
+			return (next == root) ? NULL : next;
+		}
+		cur = master;
+	} while (cur != root);
+	return NULL;
+}
+
+void propagate_remount(struct mount *mnt)
+{
+	struct mount *m = mnt;
+	struct super_block *sb = mnt->mnt.mnt_sb;
+
+	if (sb->s_op->copy_mnt_data) {
+		m = next_descendent(mnt, m);
+		while (m) {
+			sb->s_op->copy_mnt_data(m->mnt.data, mnt->mnt.data);
+			m = next_descendent(mnt, m);
+		}
+	}
+}

fs/pnode.h

@@ -44,6 +44,7 @@ int propagate_mnt(struct mount *, struct mountpoint *, struct mount *,
 int propagate_umount(struct list_head *);
 int propagate_mount_busy(struct mount *, int);
 void propagate_mount_unlock(struct mount *);
+void propagate_remount(struct mount *);
 void mnt_release_group_id(struct mount *);
 int get_dominating_id(struct mount *mnt, const struct path *root);
 unsigned int mnt_get_count(struct mount *mnt);

include/linux/fs.h

@@ -1861,6 +1861,8 @@ struct super_operations {
 	int (*unfreeze_fs) (struct super_block *);
 	int (*statfs) (struct dentry *, struct kstatfs *);
 	int (*remount_fs) (struct super_block *, int *, char *);
+	void *(*clone_mnt_data) (void *);
+	void (*copy_mnt_data) (void *, void *);
 	void (*umount_begin) (struct super_block *);
 
 	int (*show_options)(struct seq_file *, struct dentry *);
@@ -2123,6 +2125,7 @@ struct file_system_type {
 #define FS_RENAME_DOES_D_MOVE	32768	/* FS will handle d_move() during rename() internally. */
 	struct dentry *(*mount) (struct file_system_type *, int,
 		       const char *, void *);
+	void *(*alloc_mnt_data) (void);
 	void (*kill_sb) (struct super_block *);
 	struct module *owner;
 	struct file_system_type * next;

include/linux/mount.h

@@ -68,6 +68,7 @@ struct vfsmount {
 	struct dentry *mnt_root;	/* root of the mounted tree */
 	struct super_block *mnt_sb;	/* pointer to superblock */
 	int mnt_flags;
+	void *data;
 } __randomize_layout;
 
 struct file; /* forward dec */