socket-util: error number to string for sockets.

For winsock2 functions, error number has to be converted to string
using FormatMessage().

Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>

lib/socket-util.c

@@ -35,6 +35,7 @@
 #include <unistd.h>
 #include "dynamic-string.h"
 #include "fatal-signal.h"
+#include "ovs-thread.h"
 #include "packets.h"
 #include "poll-loop.h"
 #include "util.h"
@@ -64,6 +65,13 @@ VLOG_DEFINE_THIS_MODULE(socket_util);
  * space for a null terminator. */
 #define MAX_UN_LEN (sizeof(((struct sockaddr_un *) 0)->sun_path) - 1)
 
+#ifdef _WIN32
+/* Buffer used by sock_strerror(). */
+DEFINE_STATIC_PER_THREAD_DATA(struct { char s[128]; },
+                              sockerror_buffer,
+                              { "" });
+#endif
+
 static int getsockopt_int(int fd, int level, int option, const char *optname,
                           int *valuep);
 
@@ -1344,3 +1352,25 @@ ss_length(const struct sockaddr_storage *ss)
         OVS_NOT_REACHED();
     }
 }
+
+/* For Windows socket calls, 'errno' is not set.  One has to call
+ * WSAGetLastError() to get the error number and then pass it to
+ * FormatMessage() (through this function) to get the correct error string.
+
+ * ovs_strerror() calls strerror_r() and would not get the correct error
+ * string for Windows sockets, but is good for POSIX. */
+const char *
+sock_strerror(int error)
+{
+#ifdef _WIN32
+    enum { BUFSIZE = sizeof sockerror_buffer_get()->s };
+    char *buffer = sockerror_buffer_get()->s;
+
+    FormatMessage(FORMAT_MESSAGE_FROM_SYSTEM
+                  | FORMAT_MESSAGE_IGNORE_INSERTS, NULL, error, 0,
+                  buffer, BUFSIZE, NULL);
+    return buffer;
+#else
+    return ovs_strerror(error);
+#endif
+}