nfsd: use DEFINE_SHOW_ATTRIBUTE to define client_info_fops

Use DEFINE_SHOW_ATTRIBUTE helper macro to simplify the code.

inode is converted from seq_file->file instead of seq_file->private in
client_info_show().

Signed-off-by: ChenXiaoSong <chenxiaosong2@huawei.com>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>

Author: ChenXiaoSong

fs/nfsd/nfs4state.c

@@ -2490,7 +2490,7 @@ static const char *cb_state2str(int state)
 
 static int client_info_show(struct seq_file *m, void *v)
 {
-	struct inode *inode = m->private;
+	struct inode *inode = file_inode(m->file);
 	struct nfs4_client *clp;
 	u64 clid;
 
@@ -2530,17 +2530,7 @@ static int client_info_show(struct seq_file *m, void *v)
 	return 0;
 }
 
-static int client_info_open(struct inode *inode, struct file *file)
-{
-	return single_open(file, client_info_show, inode);
-}
-
-static const struct file_operations client_info_fops = {
-	.open		= client_info_open,
-	.read		= seq_read,
-	.llseek		= seq_lseek,
-	.release	= single_release,
-};
+DEFINE_SHOW_ATTRIBUTE(client_info);
 
 static void *states_start(struct seq_file *s, loff_t *pos)
 	__acquires(&clp->cl_lock)