[net/9p] readdir zerocopy changes for 9P2000.L protocol.

Modify p9_client_readdir() to check the transport preference and act according
If the preference is P9_TRANS_PREF_PAYLOAD_SEP, send the payload
separately instead of putting it directly on PDU.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>
diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index 7bca242..2ce515b 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -125,6 +125,15 @@
 	return 0;
 }
 
+static size_t
+pdu_write_readdir(struct p9_fcall *pdu, const char *kdata, size_t size)
+{
+	BUG_ON(pdu->size > P9_READDIRHDRSZ);
+	pdu->pkbuf = (char *)kdata;
+	pdu->pbuf_size = size;
+	return 0;
+}
+
 /*
 	b - int8_t
 	w - int16_t
@@ -466,6 +475,15 @@
 					errcode = -EFAULT;
 			 }
 			 break;
+		case 'F':{
+				 int32_t cnt = va_arg(ap, int32_t);
+				 const char *k = va_arg(ap, const void *);
+				 errcode = p9pdu_writef(pdu, proto_version, "d",
+						 cnt);
+				 if (!errcode && pdu_write_readdir(pdu, k, cnt))
+					errcode = -EFAULT;
+			 }
+			 break;
 		case 'U':{
 				int32_t count = va_arg(ap, int32_t);
 				const char __user *udata =