add locking to prevent file update problemsdebian/0.99.9-4

The vyatta-interfaces script needs to update the linkstatus file,
so locking is needed to prevent concurrent read/update problems.

1 files changed, 19 insertions, 1 deletions

diff --git a/watchlink/netlink_linkstatus.cc b/watchlink/netlink_linkstatus.cc
index 191625f7..9dd26fbd 100644
--- a/watchlink/netlink_linkstatus.cc
+++ b/watchlink/netlink_linkstatus.cc
@@ -8,9 +8,12 @@
  */
 #include <stdio.h>
 #include <sys/socket.h>
+#include <sys/file.h>
 #include <iostream>
 #include <string>
 #include <syslog.h>
+#include <errno.h>
+
 #include "rl_str_proc.hh"
 #include "netlink_send.hh"
 #include "netlink_event.hh"
@@ -138,11 +141,19 @@ NetlinkLinkStatus::process_going_up(const NetlinkEvent &event)
   string file = _link_dir + "/" + buf;
   FILE *fp = fopen(file.c_str(), "r");
   if (fp == NULL) {
-    syslog(LOG_INFO,"NetlinkLinkStatus::process_going_up(), failed to open state file");
+      syslog(LOG_INFO,"NetlinkLinkStatus::process_going_up(), failed to open state file: %s",
+	     strerror(errno));
     //    cerr << "NetlinkLinkStatus::process_going_up(), failed to open state file" << endl;
     return -1; //means we are still up, ignore...
   }
 
+  if (flock(fileno(fp), LOCK_SH)) {
+      syslog(LOG_INFO, "NetlinkLinkStatus::process_going_up() failed to acquire lock: %s",
+	     strerror(errno));
+      fclose(fp);
+      return -1;
+  }
+
   char str[1025];
   while (fgets(str, 1024, fp)) {
     string line(str);
@@ -233,6 +244,13 @@ NetlinkLinkStatus::process_down(const NetlinkEvent &event)
     return -1; 
   }
 
+  if (flock(fileno(fp), LOCK_EX)) {
+      syslog(LOG_INFO, "NetlinkLinkStatus::process_down() failed to acquire lock: %s",
+	     strerror(errno));
+      fclose(fp);
+      return -1;
+  }
+
   int ifindex = event.get_index();
   uint32_t local_addr = event.get_local_addr().get();
   int mask_len = event.get_mask_len();