RPC: Allow struc xdr_stream to read the page section of an xdr_buf

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>

include/linux/sunrpc/xdr.h

@@ -194,6 +194,7 @@ extern void xdr_write_pages(struct xdr_stream *xdr, struct page **pages,
 extern void xdr_init_decode(struct xdr_stream *xdr, struct xdr_buf *buf, uint32_t *p);
 extern uint32_t *xdr_inline_decode(struct xdr_stream *xdr, size_t nbytes);
 extern void xdr_read_pages(struct xdr_stream *xdr, unsigned int len);
+extern void xdr_enter_page(struct xdr_stream *xdr, unsigned int len);
 
 #endif /* __KERNEL__ */
 

net/sunrpc/xdr.c

@@ -568,8 +568,7 @@ EXPORT_SYMBOL(xdr_inline_decode);
  *
  * Moves data beyond the current pointer position from the XDR head[] buffer
  * into the page list. Any data that lies beyond current position + "len"
- * bytes is moved into the XDR tail[]. The current pointer is then
- * repositioned at the beginning of the XDR tail.
+ * bytes is moved into the XDR tail[].
  */
 void xdr_read_pages(struct xdr_stream *xdr, unsigned int len)
 {
@@ -606,6 +605,31 @@ void xdr_read_pages(struct xdr_stream *xdr, unsigned int len)
 }
 EXPORT_SYMBOL(xdr_read_pages);
 
+/**
+ * xdr_enter_page - decode data from the XDR page
+ * @xdr: pointer to xdr_stream struct
+ * @len: number of bytes of page data
+ *
+ * Moves data beyond the current pointer position from the XDR head[] buffer
+ * into the page list. Any data that lies beyond current position + "len"
+ * bytes is moved into the XDR tail[]. The current pointer is then
+ * repositioned at the beginning of the first XDR page.
+ */
+void xdr_enter_page(struct xdr_stream *xdr, unsigned int len)
+{
+	char * kaddr = page_address(xdr->buf->pages[0]);
+	xdr_read_pages(xdr, len);
+	/*
+	 * Position current pointer at beginning of tail, and
+	 * set remaining message length.
+	 */
+	if (len > PAGE_CACHE_SIZE - xdr->buf->page_base)
+		len = PAGE_CACHE_SIZE - xdr->buf->page_base;
+	xdr->p = (uint32_t *)(kaddr + xdr->buf->page_base);
+	xdr->end = (uint32_t *)((char *)xdr->p + len);
+}
+EXPORT_SYMBOL(xdr_enter_page);
+
 static struct kvec empty_iov = {.iov_base = NULL, .iov_len = 0};
 
 void