SUNRPC: Refactor logic to NUL-terminate strings in pages

Clean up: Introduce a helper to '\0'-terminate XDR strings
that are placed in a page in the page cache.

Signed-off-by: Chuck Lever <[e-mail]>
Signed-off-by: Trond Myklebust <[e-mail]>

fs/nfs/nfs2xdr.c

···
 	struct kvec *iov = rcvbuf->head;
 	size_t hdrlen;
 	u32 len, recvd;
-	char	*kaddr;
 	int	status;
 
 	if ((status = ntohl(*p++)))
···
 		return -EIO;
 	}
 
-	/* NULL terminate the string we got */
-	kaddr = (char *)kmap_atomic(rcvbuf->pages[0], KM_USER0);
-	kaddr[len+rcvbuf->page_base] = '\0';
-	kunmap_atomic(kaddr, KM_USER0);
+	xdr_terminate_string(rcvbuf, len);
 	return 0;
 }
 

fs/nfs/nfs3xdr.c

···
 	struct kvec *iov = rcvbuf->head;
 	size_t hdrlen;
 	u32 len, recvd;
-	char	*kaddr;
 	int	status;
 
 	status = ntohl(*p++);
···
 		return -EIO;
 	}
 
-	/* NULL terminate the string we got */
-	kaddr = (char*)kmap_atomic(rcvbuf->pages[0], KM_USER0);
-	kaddr[len+rcvbuf->page_base] = '\0';
-	kunmap_atomic(kaddr, KM_USER0);
+	xdr_terminate_string(rcvbuf, len);
 	return 0;
 }
 

fs/nfs/nfs4xdr.c

···
 	size_t hdrlen;
 	u32 len, recvd;
 	__be32 *p;
-	char *kaddr;
 	int status;
 
 	status = decode_op_hdr(xdr, OP_READLINK);
···
 	 * and and null-terminate the text (the VFS expects
 	 * null-termination).
 	 */
-	kaddr = (char *)kmap_atomic(rcvbuf->pages[0], KM_USER0);
-	kaddr[len+rcvbuf->page_base] = '\0';
-	kunmap_atomic(kaddr, KM_USER0);
+	xdr_terminate_string(rcvbuf, len);
 	return 0;
 out_overflow:
 	print_overflow_msg(__func__, xdr);

include/linux/sunrpc/xdr.h

···
 			 unsigned int);
 void	xdr_inline_pages(struct xdr_buf *, unsigned int,
 			 struct page **, unsigned int, unsigned int);
+void	xdr_terminate_string(struct xdr_buf *, const u32);
 
 static inline __be32 *xdr_encode_array(__be32 *p, const void *s, unsigned int len)
 {

net/sunrpc/xdr.c

···
 }
 EXPORT_SYMBOL_GPL(xdr_decode_string_inplace);
 
+/**
+ * xdr_terminate_string - '\0'-terminate a string residing in an xdr_buf
+ * @buf: XDR buffer where string resides
+ * @len: length of string, in bytes
+ *
+ */
+void
+xdr_terminate_string(struct xdr_buf *buf, const u32 len)
+{
+	char *kaddr;
+
+	kaddr = kmap_atomic(buf->pages[0], KM_USER0);
+	kaddr[buf->page_base + len] = '\0';
+	kunmap_atomic(kaddr, KM_USER0);
+}
+EXPORT_SYMBOL(xdr_terminate_string);
+
 void
 xdr_encode_pages(struct xdr_buf *xdr, struct page **pages, unsigned int base,
 		 unsigned int len)