Re: [PATCH 2/3] change libfs sb creation routines to avoid collisions with their root inodes

[Jeff Layton <jlayton@redhat.com>]

This patch makes it so that simple_fill_super and get_sb_pseudo assign their
root inodes to be number 1. It also fixes up a couple of callers of
simple_fill_super that were passing in files arrays that had an index at
number 1, and adds a warning for any caller that sends in such an array.

It would have been nice to have made it so that it wasn't possible to make
such a collision, but some callers need to be able to control what inode
number their entries get, so I think this is the best that can be done.

Signed-off-by: Jeff Layton <jlayton@redhat.com>

diff --git a/drivers/infiniband/hw/ipath/ipath_fs.c b/drivers/infiniband/hw/ipath/ipath_fs.c
index 79a60f0..6ce7926 100644
--- a/drivers/infiniband/hw/ipath/ipath_fs.c
+++ b/drivers/infiniband/hw/ipath/ipath_fs.c
@@ -510,7 +510,7 @@ static int ipathfs_fill_super(struct super_block *sb, void *data,
 	int ret;
 
 	static struct tree_descr files[] = {
-		[1] = {"atomic_stats", &atomic_stats_ops, S_IRUGO},
+		[2] = {"atomic_stats", &atomic_stats_ops, S_IRUGO},
 		{""},
 	};
 
diff --git a/fs/binfmt_misc.c b/fs/binfmt_misc.c
index c2e0825..023d825 100644
--- a/fs/binfmt_misc.c
+++ b/fs/binfmt_misc.c
@@ -727,8 +727,8 @@ static struct super_operations s_ops = {
 static int bm_fill_super(struct super_block * sb, void * data, int silent)
 {
 	static struct tree_descr bm_files[] = {
-		[1] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
-		[2] = {"register", &bm_register_operations, S_IWUSR},
+		[2] = {"status", &bm_status_operations, S_IWUSR|S_IRUGO},
+		[3] = {"register", &bm_register_operations, S_IWUSR},
 		/* last one */ {""}
 	};
 	int err = simple_fill_super(sb, 0x42494e4d, bm_files);
diff --git a/fs/inode.c b/fs/inode.c
diff --git a/fs/libfs.c b/fs/libfs.c
index 503898d..9b77f89 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -217,6 +217,12 @@ int get_sb_pseudo(struct file_system_type *fs_type, char *name,
 	root = new_inode(s);
 	if (!root)
 		goto Enomem;
+	/*
+	 * since this is the first inode, make it number 1. New inodes created
+	 * after this must take care not to collide with it (by passing
+	 * max_reserved of 1 to iunique).
+	 */
+	root->i_ino = 1;
 	root->i_mode = S_IFDIR | S_IRUSR | S_IWUSR;
 	root->i_uid = root->i_gid = 0;
 	root->i_atime = root->i_mtime = root->i_ctime = CURRENT_TIME;
@@ -356,6 +362,11 @@ int simple_commit_write(struct file *file, struct page *page,
 	return 0;
 }
 
+/*
+ * the inodes created here are not hashed. If you use iunique to generate
+ * unique inode values later for this filesystem, then you must take care
+ * to pass it an appropriate max_reserved value to avoid collisions.
+ */
 int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files)
 {
 	static struct super_operations s_ops = {.statfs = simple_statfs};
@@ -373,6 +384,11 @@ int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files
 	inode = new_inode(s);
 	if (!inode)
 		return -ENOMEM;
+	/*
+	 * because the root inode is 1, the files array must not contain an
+	 * entry at index 1
+	 */
+	inode->i_ino = 1;
 	inode->i_mode = S_IFDIR | 0755;
 	inode->i_uid = inode->i_gid = 0;
 	inode->i_blocks = 0;
@@ -388,6 +404,13 @@ int simple_fill_super(struct super_block *s, int magic, struct tree_descr *files
 	for (i = 0; !files->name || files->name[0]; i++, files++) {
 		if (!files->name)
 			continue;
+
+		/* warn if it tries to conflict with the root inode */
+		if (unlikely(i == 1))
+			printk(KERN_WARNING "%s: %s passed in a files array"
+				"with an index of 1!\n", __func__,
+				s->s_type->name);
+
 		dentry = d_alloc_name(root, files->name);
 		if (!dentry)
 			goto out;