nfsd: formally deprecate legacy nfsd syscall interface

The syscall interface is has been replaced by a more flexible
interface since 2.6.0.  It is time to work towards discarding
the old interface.

So add a entry in feature-removal-schedule.txt and print a warning
when the interface is used.
Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

Documentation/feature-removal-schedule.txt

@@ -564,3 +564,13 @@ Who:	FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
 
 ----------------------------
 
+What:   access to nfsd auth cache through sys_nfsservctl or '.' files
+        in the 'nfsd' filesystem.
+When:   2.6.40
+Why:    This is a legacy interface which have been replaced by a more
+        dynamic cache.  Continuing to maintain this interface is an
+        unnecessary burden.
+Who:    NeilBrown <neilb@suse.de>
+
+----------------------------
+	

fs/nfsd/nfsctl.c

@@ -121,6 +121,16 @@ static ssize_t nfsctl_transaction_write(struct file *file, const char __user *bu
 
 static ssize_t nfsctl_transaction_read(struct file *file, char __user *buf, size_t size, loff_t *pos)
 {
+	static int warned;
+	if (file->f_dentry->d_name.name[0] == '.' && !warned) {
+		char name[sizeof(current->comm)];
+		printk(KERN_INFO
+		       "Warning: \"%s\" uses deprecated NFSD interface: %s."
+		       "  This will be removed in 2.6.40\n",
+		       get_task_comm(name, current),
+		       file->f_dentry->d_name.name);
+		warned = 1;
+	}
 	if (! file->private_data) {
 		/* An attempt to read a transaction file without writing
 		 * causes a 0-byte write so that the file can return