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

Modify p9_client_read() to check the transport preference and act accordingly.
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>

net/9p/client.c

@@ -1270,7 +1270,15 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
 	if (count < rsize)
 		rsize = count;
 
-	req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset, rsize);
+	/* Don't bother zerocopy form small IO (< 1024) */
+	if (((clnt->trans_mod->pref & P9_TRANS_PREF_PAYLOAD_MASK) ==
+			P9_TRANS_PREF_PAYLOAD_SEP) && (rsize > 1024)) {
+		req = p9_client_rpc(clnt, P9_TREAD, "dqE", fid->fid, offset,
+				rsize, data, udata);
+	} else {
+		req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
+				rsize);
+	}
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		goto error;
@@ -1284,13 +1292,15 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
 
 	P9_DPRINTK(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
 
-	if (data) {
-		memmove(data, dataptr, count);
-	} else {
-		err = copy_to_user(udata, dataptr, count);
-		if (err) {
-			err = -EFAULT;
-			goto free_and_error;
+	if (!req->tc->pbuf_size) {
+		if (data) {
+			memmove(data, dataptr, count);
+		} else {
+			err = copy_to_user(udata, dataptr, count);
+			if (err) {
+				err = -EFAULT;
+				goto free_and_error;
+			}
 		}
 	}
 	p9_free_req(clnt, req);

net/9p/protocol.c

@@ -114,6 +114,17 @@ pdu_write_u(struct p9_fcall *pdu, const char __user *udata, size_t size)
 	return size - len;
 }
 
+static size_t
+pdu_write_urw(struct p9_fcall *pdu, const char *kdata, const char __user *udata,
+		size_t size)
+{
+	BUG_ON(pdu->size > P9_IOHDRSZ);
+	pdu->pubuf = (char __user *)udata;
+	pdu->pkbuf = (char *)kdata;
+	pdu->pbuf_size = size;
+	return 0;
+}
+
 /*
 	b - int8_t
 	w - int16_t
@@ -445,6 +456,16 @@ p9pdu_vwritef(struct p9_fcall *pdu, int proto_version, const char *fmt,
 					errcode = -EFAULT;
 			}
 			break;
+		case 'E':{
+				 int32_t cnt = va_arg(ap, int32_t);
+				 const char *k = va_arg(ap, const void *);
+				 const char *u = va_arg(ap, const void *);
+				 errcode = p9pdu_writef(pdu, proto_version, "d",
+						 cnt);
+				 if (!errcode && pdu_write_urw(pdu, k, u, cnt))
+					errcode = -EFAULT;
+			 }
+			 break;
 		case 'U':{
 				int32_t count = va_arg(ap, int32_t);
 				const char __user *udata =