nfsd4: fix minorversion support interface

You can turn on or off support for minorversions using e.g.

	echo "-4.2" >/proc/fs/nfsd/versions

However, the current implementation is a little wonky.  For example, the
above will turn off 4.2 support, but it will also turn *on* 4.1 support.

This didn't matter as long as we only had 2 minorversions, which was
true till very recently.

And do a little cleanup here.
Signed-off-by: J. Bruce Fields <bfields@redhat.com>

fs/nfsd/nfs4proc.c

@@ -1293,7 +1293,7 @@ nfsd4_proc_compound(struct svc_rqst *rqstp,
 	 * According to RFC3010, this takes precedence over all other errors.
 	 */
 	status = nfserr_minor_vers_mismatch;
-	if (args->minorversion > nfsd_supported_minorversion)
+	if (nfsd_minorversion(args->minorversion, NFSD_TEST) <= 0)
 		goto out;
 
 	status = nfs41_check_op_ordering(args);

fs/nfsd/nfsd.h

@@ -53,7 +53,6 @@ struct readdir_cd {
 extern struct svc_program	nfsd_program;
 extern struct svc_version	nfsd_version2, nfsd_version3,
 				nfsd_version4;
-extern u32			nfsd_supported_minorversion;
 extern struct mutex		nfsd_mutex;
 extern spinlock_t		nfsd_drc_lock;
 extern unsigned long		nfsd_drc_max_mem;

fs/nfsd/nfssvc.c

@@ -116,7 +116,10 @@ struct svc_program		nfsd_program = {
 
 };
 
-u32 nfsd_supported_minorversion = 1;
+static bool nfsd_supported_minorversions[NFSD_SUPPORTED_MINOR_VERSION + 1] = {
+	[0] = 1,
+	[1] = 1,
+};
 
 int nfsd_vers(int vers, enum vers_op change)
 {
@@ -151,15 +154,13 @@ int nfsd_minorversion(u32 minorversion, enum vers_op change)
 		return -1;
 	switch(change) {
 	case NFSD_SET:
-		nfsd_supported_minorversion = minorversion;
+		nfsd_supported_minorversions[minorversion] = true;
 		break;
 	case NFSD_CLEAR:
-		if (minorversion == 0)
-			return -1;
-		nfsd_supported_minorversion = minorversion - 1;
+		nfsd_supported_minorversions[minorversion] = false;
 		break;
 	case NFSD_TEST:
-		return minorversion <= nfsd_supported_minorversion;
+		return nfsd_supported_minorversions[minorversion];
 	case NFSD_AVAIL:
 		return minorversion <= NFSD_SUPPORTED_MINOR_VERSION;
 	}