nl: Provide API to specify the default buffer size when receiving netlink messages

New functions:
  nl_socket_set_msg_buf_size(sk, size)
  nl_socket_get_msg_buf_size(sk)

Default remains getpagesize()

Signed-off-by: Thomas Graf <tgraf@redhat.com>

4 files changed, 34 insertions, 1 deletions

diff --git a/include/netlink-types.h b/include/netlink-types.h
index 2e80b05..e885571 100644
--- a/include/netlink-types.h
+++ b/include/netlink-types.h
@@ -69,6 +69,7 @@ struct nl_sock
 	unsigned int		s_seq_expect;
 	int			s_flags;
 	struct nl_cb *		s_cb;
+	size_t			s_bufsize;
 };
 
 struct nl_cache
diff --git a/include/netlink/socket.h b/include/netlink/socket.h
index d0f5a6a..1007eba 100644
--- a/include/netlink/socket.h
+++ b/include/netlink/socket.h
@@ -49,6 +49,8 @@ extern int nl_socket_modify_err_cb(struct nl_sock *, enum nl_cb_kind,
 				   nl_recvmsg_err_cb_t, void *);
 
 extern int		nl_socket_set_buffer_size(struct nl_sock *, int, int);
+extern int		nl_socket_set_msg_buf_size(struct nl_sock *, size_t);
+extern size_t		nl_socket_get_msg_buf_size(struct nl_sock *);
 extern int		nl_socket_set_passcred(struct nl_sock *, int);
 extern int		nl_socket_recv_pktinfo(struct nl_sock *, int);
 
diff --git a/lib/nl.c b/lib/nl.c
index ea3e087..5b37c2a 100644
--- a/lib/nl.c
+++ b/lib/nl.c
@@ -447,7 +447,7 @@ int nl_recv(struct nl_sock *sk, struct sockaddr_nl *nla,
 	if (page_size == 0)
 		page_size = getpagesize();
 
-	iov.iov_len = page_size;
+	iov.iov_len = sk->s_bufsize ? : page_size;
 	iov.iov_base = *buf = malloc(iov.iov_len);
 
 	if (sk->s_flags & NL_SOCK_PASSCRED) {
diff --git a/lib/socket.c b/lib/socket.c
index 7e3ebf6..d53a714 100644
--- a/lib/socket.c
+++ b/lib/socket.c
@@ -587,6 +587,36 @@ int nl_socket_set_buffer_size(struct nl_sock *sk, int rxbuf, int txbuf)
 }
 
 /**
+ * Set default message buffer size of netlink socket.
+ * @arg sk		Netlink socket.
+ * @arg bufsize		Default message buffer size in bytes.
+ *
+ * Sets the default message buffer size to the specified length in bytes.
+ * The default message buffer size limits the maximum message size the
+ * socket will be able to receive. It is generally recommneded to specify
+ * a buffer size no less than the size of a memory page.
+ *
+ * @return 0 on success or a negative error code.
+ */
+int nl_socket_set_msg_buf_size(struct nl_sock *sk, size_t bufsize)
+{
+	sk->s_bufsize = bufsize;
+
+	return 0;
+}
+
+/**
+ * Get default message buffer size of netlink socket.
+ * @arg sk		Netlink socket.
+ *
+ * @return Size of default message buffer.
+ */
+size_t nl_socket_get_msg_buf_size(struct nl_sock *sk)
+{
+	return sk->s_bufsize;
+}
+
+/**
  * Enable/disable credential passing on netlink socket.
  * @arg sk		Netlink socket.
  * @arg state		New state (0 - disabled, 1 - enabled)