[RFC] [PATCH 1/7] [net/9p] Additional elements to p9_fcall to accomodate zero copy.

["Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com>]

In addition, this patch also avoids zero copy for short reads in !dotl case.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>

Conflicts:

	net/9p/protocol.c
---
 include/net/9p/9p.h |    2 +
 net/9p/client.c     |   74 +++++++++++++++++++++++++++++++++-----------------
 2 files changed, 51 insertions(+), 25 deletions(-)

diff --git a/include/net/9p/9p.h b/include/net/9p/9p.h
index 9c939c2..7313801 100644
--- a/include/net/9p/9p.h
+++ b/include/net/9p/9p.h
@@ -320,6 +320,8 @@ enum p9_qid_t {
 /* Room for readdir header */
 #define P9_READDIRHDRSZ	24
 
+#define P9_ERRMAX 256 /* FIXME: Check what is the correct value */
+
 /**
  * struct p9_str - length prefixed string type
  * @len: length of the string
diff --git a/net/9p/client.c b/net/9p/client.c
index f939edf..7f34c42 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -443,6 +443,7 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 {
 	int8_t type;
 	int err;
+	int ecode;
 
 	err = p9_parse_header(req->rc, NULL, &type, NULL, 0);
 	if (err) {
@@ -450,36 +451,53 @@ static int p9_check_errors(struct p9_client *c, struct p9_req_t *req)
 		return err;
 	}
 
-	if (type == P9_RERROR || type == P9_RLERROR) {
-		int ecode;
-
-		if (!p9_is_proto_dotl(c)) {
-			char *ename;
+	if (type != P9_RERROR && type != P9_RLERROR) 
+		return 0;
 
-			err = p9pdu_readf(req->rc, c->proto_version, "s?d",
-								&ename, &ecode);
-			if (err)
-				goto out_err;
+	if (!p9_is_proto_dotl(c)) {
+		char *ename;
+
+		if (req->tc->pbuf_size) {
+			/* Handle user buffers */
+			size_t len = req->rc->size - req->rc->offset;
+			if (req->tc->pbuf &&
+					!segment_eq(get_fs(), KERNEL_DS)) {
+				/* User Buffer */
+				err = copy_from_user(
+					&req->rc->sdata[req->rc->offset],
+					req->tc->pbuf, len);
+				if (err) {
+					err = -EFAULT;
+					return err;
+				}
+			} else {
+				/* Kernel Buffer */
+				memmove(&req->rc->sdata[req->rc->offset],
+						req->tc->pbuf, len);
+			}
+		}
+		err = p9pdu_readf(req->rc, c->proto_version, "s?d",
+				&ename, &ecode);
+		if (err)
+			goto out_err;
 
-			if (p9_is_proto_dotu(c))
-				err = -ecode;
+		if (p9_is_proto_dotu(c))
+			err = -ecode;
 
-			if (!err || !IS_ERR_VALUE(err)) {
-				err = p9_errstr2errno(ename, strlen(ename));
+		if (!err || !IS_ERR_VALUE(err)) {
+			err = p9_errstr2errno(ename, strlen(ename));
 
-				P9_DPRINTK(P9_DEBUG_9P, "<<< RERROR (%d) %s\n", -ecode, ename);
+			P9_DPRINTK(P9_DEBUG_9P, "<<< RERROR (%d) %s\n", -ecode, ename);
 
-				kfree(ename);
-			}
-		} else {
-			err = p9pdu_readf(req->rc, c->proto_version, "d", &ecode);
-			err = -ecode;
-
-			P9_DPRINTK(P9_DEBUG_9P, "<<< RLERROR (%d)\n", -ecode);
+			kfree(ename);
 		}
+	} else {
+		err = p9pdu_readf(req->rc, c->proto_version, "d", &ecode);
+		err = -ecode;
+
+		P9_DPRINTK(P9_DEBUG_9P, "<<< RLERROR (%d)\n", -ecode);
+	}
 
-	} else
-		err = 0;
 
 	return err;
 
@@ -1270,8 +1288,14 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
 	if (count < rsize)
 		rsize = count;
 
-	if ((clnt->trans_mod->pref & P9_TRANS_PREF_PAYLOAD_MASK) ==
-			P9_TRANS_PREF_PAYLOAD_SEP) {
+	/* for !p9_proto_2000L, we need to have enough space on PDU
+	 * to handle TREAD/RERROR. Hence don't attempt payload
+	 * seperaion for small reads even if the transport prefers
+	 * P9_TRANS_PREF_PAYLOAD_SEP */
+	if (((clnt->trans_mod->pref & P9_TRANS_PREF_PAYLOAD_MASK) ==
+			P9_TRANS_PREF_PAYLOAD_SEP) &&
+			((clnt->proto_version == p9_proto_2000L) ||
+			 rsize > 2 * P9_ERRMAX) ) {
 		req = p9_client_rpc(clnt, P9_TREAD, "dqE", fid->fid, offset,
 				rsize, data ? data : udata);
 	} else {
-- 
1.6.5.2