[net/9p] Preparation and helper functions for zero copy

This patch prepares p9_fcall structure for zero copy. Added
fields send the payload buffer information to the transport layer.
In addition it adds a 'private' field for the transport layer to
store mapped/pinned page information so that it can be freed/unpinned
during req_done.

This patch also creates trans_common.[ch] to house helper functions.
It adds the following helper functions.

p9_release_req_pages - Release pages after the transaction.
p9_nr_pages - Return number of pages needed to accomodate the payload.
payload_gup - Translates user buffer into kernel pages.

Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
Signed-off-by: Eric Van Hensbergen <ericvh@gmail.com>

1 files changed, 4 insertions, 0 deletions

diff --git a/net/9p/protocol.c b/net/9p/protocol.c
index 1e308f210928..d888847db56e 100644
--- a/net/9p/protocol.c
+++ b/net/9p/protocol.c
@@ -606,6 +606,10 @@ void p9pdu_reset(struct p9_fcall *pdu)
 {
         pdu->offset = 0;
         pdu->size = 0;
+        pdu->private = NULL;
+        pdu->pubuf = NULL;
+        pdu->pkbuf = NULL;
+        pdu->pbuf_size = 0;
 }
 
 int p9dirent_read(char *buf, int len, struct p9_dirent *dirent,