inode numbering: change libfs sb creation routines to avoid collisions with their root inodes

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>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 23 insertions, 0 deletions

diff --git a/fs/libfs.c b/fs/libfs.c
index d93842d3c0a0..1247ee90253a 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -220,6 +220,12 @@ 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;
@@ -360,6 +366,11 @@ 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)
 {
         struct inode *inode;
@@ -376,6 +387,11 @@ 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;
@@ -391,6 +407,13 @@ 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;