From 8b8a4148ec14363d75ad76c1fb9542c85b66b8c5 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Petr=20Men=C5=A1=C3=ADk?= <pemensik@redhat.com>
Date: Tue, 2 Mar 2021 21:36:45 +0000
Subject: [PATCH] Move flags to recvmsg function in netlink

netlink_multicast used 3 calls to fcntl in order to set O_NONBLOCK on
socket. It is possible to pass MSG_DONTWAIT flag just to recvmsg function,
without setting it permanently on socket. Save few kernel calls and use
recvmsg flags.

It is supported since kernel 2.2, should be fine for any device still
receiving updates.
---
 src/netlink.c | 19 ++++++-------------
 1 file changed, 6 insertions(+), 13 deletions(-)

diff --git a/src/netlink.c b/src/netlink.c
index 3ad18a6..9762bfa 100644
--- a/src/netlink.c
+++ b/src/netlink.c
@@ -102,7 +102,7 @@ char *netlink_init(void)
   return NULL;
 }
 
-static ssize_t netlink_recv(void)
+static ssize_t netlink_recv(int flags)
 {
   struct msghdr msg;
   struct sockaddr_nl nladdr;
@@ -118,7 +118,8 @@ static ssize_t netlink_recv(void)
       msg.msg_iovlen = 1;
       msg.msg_flags = 0;
       
-      while ((rc = recvmsg(daemon->netlinkfd, &msg, MSG_PEEK | MSG_TRUNC)) == -1 && errno == EINTR);
+      while ((rc = recvmsg(daemon->netlinkfd, &msg, flags | MSG_PEEK | MSG_TRUNC)) == -1 &&
+	     errno == EINTR);
       
       /* make buffer big enough */
       if (rc != -1 && (msg.msg_flags & MSG_TRUNC))
@@ -135,7 +136,7 @@ static ssize_t netlink_recv(void)
 
       /* read it for real */
       msg.msg_flags = 0;
-      while ((rc = recvmsg(daemon->netlinkfd, &msg, 0)) == -1 && errno == EINTR);
+      while ((rc = recvmsg(daemon->netlinkfd, &msg, flags)) == -1 && errno == EINTR);
       
       /* Make sure this is from the kernel */
       if (rc == -1 || nladdr.nl_pid == 0)
@@ -198,7 +199,7 @@ int iface_enumerate(int family, void *parm, int (*callback)())
     
   while (1)
     {
-      if ((len = netlink_recv()) == -1)
+      if ((len = netlink_recv(0)) == -1)
 	{
 	  if (errno == ENOBUFS)
 	    {
@@ -350,22 +351,14 @@ static void nl_multicast_state(unsigned state)
 {
   ssize_t len;
   struct nlmsghdr *h;
-  int flags;
-
-  if ((flags = fcntl(daemon->netlinkfd, F_GETFL)) == -1 ||
-      fcntl(daemon->netlinkfd, F_SETFL, flags | O_NONBLOCK) == -1) 
-    return;
 
   do {
     /* don't risk blocking reading netlink messages here. */
-    while ((len = netlink_recv()) != -1)
+    while ((len = netlink_recv(MSG_DONTWAIT)) != -1)
   
       for (h = (struct nlmsghdr *)iov.iov_base; NLMSG_OK(h, (size_t)len); h = NLMSG_NEXT(h, len))
 	state = nl_async(h, state);
   } while (errno == ENOBUFS);
-
-  /* restore non-blocking status */
-  fcntl(daemon->netlinkfd, F_SETFL, flags);
 }
 
 void netlink_multicast(void)