[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, 97 insertions, 0 deletions

diff --git a/net/9p/trans_common.c b/net/9p/trans_common.c
new file mode 100644
index 000000000000..d62b9aa58df8
--- /dev/null
+++ b/net/9p/trans_common.c
@@ -0,0 +1,97 @@
+/*
+ * Copyright IBM Corporation, 2010
+ * Author Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify it
+ * under the terms of version 2.1 of the GNU Lesser General Public License
+ * as published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it would be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
+ *
+ */
+
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <net/9p/9p.h>
+#include <net/9p/client.h>
+#include <linux/scatterlist.h>
+#include "trans_common.h"
+
+/**
+ *  p9_release_req_pages - Release pages after the transaction.
+ *  @*private: PDU's private page of struct trans_rpage_info
+ */
+void
+p9_release_req_pages(struct trans_rpage_info *rpinfo)
+{
+	int i = 0;
+
+	while (rpinfo->rp_data[i] && rpinfo->rp_nr_pages--) {
+		put_page(rpinfo->rp_data[i]);
+		i++;
+	}
+}
+EXPORT_SYMBOL(p9_release_req_pages);
+
+/**
+ * p9_nr_pages - Return number of pages needed to accomodate the payload.
+ */
+int
+p9_nr_pages(struct p9_req_t *req)
+{
+	int start_page, end_page;
+	start_page =  (unsigned long long)req->tc->pubuf >> PAGE_SHIFT;
+	end_page = ((unsigned long long)req->tc->pubuf + req->tc->pbuf_size +
+			PAGE_SIZE - 1) >> PAGE_SHIFT;
+	return end_page - start_page;
+}
+EXPORT_SYMBOL(p9_nr_pages);
+
+/**
+ * payload_gup - Translates user buffer into kernel pages and
+ * pins them either for read/write through get_user_pages_fast().
+ * @req: Request to be sent to server.
+ * @pdata_off: data offset into the first page after translation (gup).
+ * @pdata_len: Total length of the IO. gup may not return requested # of pages.
+ * @nr_pages: number of pages to accomodate the payload
+ * @rw: Indicates if the pages are for read or write.
+ */
+int
+p9_payload_gup(struct p9_req_t *req, size_t *pdata_off, int *pdata_len,
+		int nr_pages, u8 rw)
+{
+	uint32_t first_page_bytes = 0;
+	uint32_t pdata_mapped_pages;
+	struct trans_rpage_info  *rpinfo;
+
+	*pdata_off = (size_t)req->tc->pubuf & (PAGE_SIZE-1);
+
+	if (*pdata_off)
+		first_page_bytes = min((PAGE_SIZE - *pdata_off),
+				req->tc->pbuf_size);
+
+	rpinfo = req->tc->private;
+	pdata_mapped_pages = get_user_pages_fast((unsigned long)req->tc->pubuf,
+			nr_pages, rw, &rpinfo->rp_data[0]);
+
+	if (pdata_mapped_pages < 0) {
+		printk(KERN_ERR "get_user_pages_fast failed:%d udata:%p"
+				"nr_pages:%d\n", pdata_mapped_pages,
+				req->tc->pubuf, nr_pages);
+		pdata_mapped_pages = 0;
+		return -EIO;
+	}
+	rpinfo->rp_nr_pages = pdata_mapped_pages;
+	if (*pdata_off) {
+		*pdata_len = first_page_bytes;
+		*pdata_len += min((req->tc->pbuf_size - *pdata_len),
+				((size_t)pdata_mapped_pages - 1) << PAGE_SHIFT);
+	} else {
+		*pdata_len = min(req->tc->pbuf_size,
+				(size_t)pdata_mapped_pages << PAGE_SHIFT);
+	}
+	return 0;
+}
+EXPORT_SYMBOL(p9_payload_gup);