libfs: support RENAME_NOREPLACE in simple_rename()

This is trivial to do:

 - add flags argument to simple_rename()
 - check if flags doesn't have any other than RENAME_NOREPLACE
 - assign simple_rename() to .rename2 instead of .rename

Filesystems converted:

hugetlbfs, ramfs, bpf.

Debugfs uses simple_rename() to implement debugfs_rename(), which is for
debugfs instances to rename files internally, not for userspace filesystem
access.  For this case pass zero flags to simple_rename().
Signed-off-by: Miklos Szeredi <mszeredi@redhat.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Alexei Starovoitov <ast@kernel.org>

fs/debugfs/inode.c

@@ -748,7 +748,7 @@ struct dentry *debugfs_rename(struct dentry *old_dir, struct dentry *old_dentry,
 	old_name = fsnotify_oldname_init(old_dentry->d_name.name);
 
 	error = simple_rename(d_inode(old_dir), old_dentry, d_inode(new_dir),
-		dentry);
+			      dentry, 0);
 	if (error) {
 		fsnotify_oldname_free(old_name);
 		goto exit;

fs/hugetlbfs/inode.c

@@ -988,7 +988,7 @@ static const struct inode_operations hugetlbfs_dir_inode_operations = {
 	.mkdir		= hugetlbfs_mkdir,
 	.rmdir		= simple_rmdir,
 	.mknod		= hugetlbfs_mknod,
-	.rename		= simple_rename,
+	.rename2	= simple_rename,
 	.setattr	= hugetlbfs_setattr,
 };
 

fs/libfs.c

@@ -349,11 +349,15 @@ int simple_rmdir(struct inode *dir, struct dentry *dentry)
 EXPORT_SYMBOL(simple_rmdir);
 
 int simple_rename(struct inode *old_dir, struct dentry *old_dentry,
-		struct inode *new_dir, struct dentry *new_dentry)
+		  struct inode *new_dir, struct dentry *new_dentry,
+		  unsigned int flags)
 {
 	struct inode *inode = d_inode(old_dentry);
 	int they_are_dirs = d_is_dir(old_dentry);
 
+	if (flags & ~RENAME_NOREPLACE)
+		return -EINVAL;
+
 	if (!simple_empty(new_dentry))
 		return -ENOTEMPTY;
 

fs/ramfs/inode.c

@@ -146,7 +146,7 @@ static const struct inode_operations ramfs_dir_inode_operations = {
 	.mkdir		= ramfs_mkdir,
 	.rmdir		= simple_rmdir,
 	.mknod		= ramfs_mknod,
-	.rename		= simple_rename,
+	.rename2	= simple_rename,
 };
 
 static const struct super_operations ramfs_ops = {

include/linux/fs.h

@@ -2950,7 +2950,8 @@ extern int simple_open(struct inode *inode, struct file *file);
 extern int simple_link(struct dentry *, struct inode *, struct dentry *);
 extern int simple_unlink(struct inode *, struct dentry *);
 extern int simple_rmdir(struct inode *, struct dentry *);
-extern int simple_rename(struct inode *, struct dentry *, struct inode *, struct dentry *);
+extern int simple_rename(struct inode *, struct dentry *,
+			 struct inode *, struct dentry *, unsigned int);
 extern int noop_fsync(struct file *, loff_t, loff_t, int);
 extern int simple_empty(struct dentry *);
 extern int simple_readpage(struct file *file, struct page *page);

kernel/bpf/inode.c

@@ -189,7 +189,7 @@ static const struct inode_operations bpf_dir_iops = {
 	.mknod		= bpf_mkobj,
 	.mkdir		= bpf_mkdir,
 	.rmdir		= simple_rmdir,
-	.rename		= simple_rename,
+	.rename2	= simple_rename,
 	.link		= simple_link,
 	.unlink		= simple_unlink,
 };