knfsd: exportfs: remove iget abuse

When the exportfs interface was added the expectation was that filesystems
provide an operation to convert from a file handle to an inode/dentry, but it
kept a backwards compat option that still calls into iget.

Calling into iget from non-filesystem code is very bad, because it gives too
little information to filesystem, and simply crashes if the filesystem doesn't
implement the ->read_inode routine.

Fortunately there are only two filesystems left using this fallback: efs and
jfs.  This patch moves a copy of export_iget to each of those to implement the
get_dentry method.

While this is a temporary increase of lines of code in the kernel it allows
for a much cleaner interface and important code restructuring in later
patches.

[[email protected]: add jfs_get_inode_flags() declaration]
Signed-off-by: Dave Kleikamp <[email protected]>
Signed-off-by: Christoph Hellwig <[email protected]>
Signed-off-by: Neil Brown <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

fs/efs/namei.c

@@ -75,6 +75,38 @@ struct dentry *efs_lookup(struct inode *dir, struct dentry *dentry, struct namei
 	return NULL;
 }
 
+struct dentry *efs_get_dentry(struct super_block *sb, void *vobjp)
+{
+	__u32 *objp = vobjp;
+	unsigned long ino = objp[0];
+	__u32 generation = objp[1];
+	struct inode *inode;
+	struct dentry *result;
+
+	if (ino == 0)
+		return ERR_PTR(-ESTALE);
+	inode = iget(sb, ino);
+	if (inode == NULL)
+		return ERR_PTR(-ENOMEM);
+
+	if (is_bad_inode(inode) ||
+	    (generation && inode->i_generation != generation)) {
+	    	result = ERR_PTR(-ESTALE);
+		goto out_iput;
+	}
+
+	result = d_alloc_anon(inode);
+	if (!result) {
+		result = ERR_PTR(-ENOMEM);
+		goto out_iput;
+	}
+	return result;
+
+ out_iput:
+	iput(inode);
+	return result;
+}
+
 struct dentry *efs_get_parent(struct dentry *child)
 {
 	struct dentry *parent;

fs/efs/super.c

@@ -114,6 +114,7 @@ static const struct super_operations efs_superblock_operations = {
 };
 
 static struct export_operations efs_export_ops = {
+	.get_dentry	= efs_get_dentry,
 	.get_parent	= efs_get_parent,
 };