9P2010.L handshake: Add mount option

Add new mount V9FS mount option to specify protocol version

This patch adds a new mount option to specify protocol version.
With this option it is possible to use "-o version=" switch to
specify 9P protocol version to use. Valid options for version
are:
9p2000
9p2000.u
9p2010.L

Signed-off-by: Sripathi Kodi <sripathik@in.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

include/net/9p/client.h

@@ -29,6 +29,19 @@
 /* Number of requests per row */
 #define P9_ROW_MAXTAG 255
 
+/** enum p9_proto_versions - 9P protocol versions
+ * @p9_proto_legacy: 9P Legacy mode, pre-9P2000.u
+ * @p9_proto_2000u: 9P2000.u extension
+ * @p9_proto_2010L: 9P2010.L extension
+ */
+
+enum p9_proto_versions{
+	p9_proto_legacy = 0,
+	p9_proto_2000u = 1,
+	p9_proto_2010L = 2,
+};
+
+
 /**
  * enum p9_trans_status - different states of underlying transports
  * @Connected: transport is connected and healthy
@@ -111,6 +124,7 @@ struct p9_req_t {
  * @lock: protect @fidlist
  * @msize: maximum data size negotiated by protocol
  * @dotu: extension flags negotiated by protocol
+ * @proto_version: 9P protocol version to use
  * @trans_mod: module API instantiated with this client
  * @trans: tranport instance state and API
  * @conn: connection state information used by trans_fd
@@ -138,6 +152,7 @@ struct p9_client {
 	spinlock_t lock; /* protect client structure */
 	int msize;
 	unsigned char dotu;
+	unsigned char proto_version;
 	struct p9_trans_module *trans_mod;
 	enum p9_trans_status status;
 	void *trans;

net/9p/client.c

@@ -46,16 +46,38 @@ enum {
 	Opt_msize,
 	Opt_trans,
 	Opt_legacy,
+	Opt_version,
 	Opt_err,
 };
 
 static const match_table_t tokens = {
 	{Opt_msize, "msize=%u"},
 	{Opt_legacy, "noextend"},
 	{Opt_trans, "trans=%s"},
+	{Opt_version, "version=%s"},
 	{Opt_err, NULL},
 };
 
+/* Interpret mount option for protocol version */
+static unsigned char get_protocol_version(const substring_t *name)
+{
+	unsigned char version = -EINVAL;
+	if (!strncmp("9p2000", name->from, name->to-name->from)) {
+		version = p9_proto_legacy;
+		P9_DPRINTK(P9_DEBUG_9P, "Protocol version: Legacy\n");
+	} else if (!strncmp("9p2000.u", name->from, name->to-name->from)) {
+		version = p9_proto_2000u;
+		P9_DPRINTK(P9_DEBUG_9P, "Protocol version: 9P2000.u\n");
+	} else if (!strncmp("9p2010.L", name->from, name->to-name->from)) {
+		version = p9_proto_2010L;
+		P9_DPRINTK(P9_DEBUG_9P, "Protocol version: 9P2010.L\n");
+	} else {
+		P9_DPRINTK(P9_DEBUG_ERROR, "Unknown protocol version %s. ",
+							name->from);
+	}
+	return version;
+}
+
 static struct p9_req_t *
 p9_client_rpc(struct p9_client *c, int8_t type, const char *fmt, ...);
 
@@ -120,6 +142,12 @@ static int parse_opts(char *opts, struct p9_client *clnt)
 		case Opt_legacy:
 			clnt->dotu = 0;
 			break;
+		case Opt_version:
+			ret = get_protocol_version(&args[0]);
+			if (ret == -EINVAL)
+				goto free_and_return;
+			clnt->proto_version = ret;
+			break;
 		default:
 			continue;
 		}