Fix compilation with VS2017

The primary issue is that in MSVC 14.00 (VS2015) Microsoft added
snprintf as a function to the standard library and prevents users from
defining it to something else (typically, this was _snprintf). So, only
define it when using _MSC_VER < 1900.

Other changes are:
- Fix macro definition of dup2
- Add macro for getpid
- Add function definition for win32_dup
- Add missing EXTERNs

Signed-off-by: Tim Crawford <crawfxrd@gmail.com>

include/iscsi.h

@@ -166,7 +166,7 @@ enum iscsi_immediate_data {
 	ISCSI_IMMEDIATE_DATA_NO  = 0,
 	ISCSI_IMMEDIATE_DATA_YES = 1
 };
-int iscsi_set_immediate_data(struct iscsi_context *iscsi, enum iscsi_immediate_data immediate_data);
+EXTERN int iscsi_set_immediate_data(struct iscsi_context *iscsi, enum iscsi_immediate_data immediate_data);
 
 /*
  * This function is used to set the desired mode for initial_r2t
@@ -179,7 +179,7 @@ enum iscsi_initial_r2t {
 	ISCSI_INITIAL_R2T_NO  = 0,
 	ISCSI_INITIAL_R2T_YES = 1
 };
-int
+EXTERN int
 iscsi_set_initial_r2t(struct iscsi_context *iscsi, enum iscsi_initial_r2t initial_r2t);
 
 

lib/init.c

@@ -22,6 +22,7 @@
 #define _GNU_SOURCE
 
 #if defined(WIN32)
+#include "win32/win32_compat.h"
 #else
 #include <strings.h>
 #include <unistd.h>

lib/socket.c

@@ -1102,7 +1102,7 @@ void iscsi_set_bind_interfaces(struct iscsi_context *iscsi, char * interfaces _U
 #endif
 }
 
-#ifdef WIN32
+#if defined(_MSC_VER) && _MSC_VER < 1900
 static iscsi_transport iscsi_transport_tcp = {
 	iscsi_tcp_connect,
 	iscsi_tcp_queue_pdu,

win32/win32_compat.h

@@ -22,9 +22,10 @@ THE SOFTWARE.
 */
 /*Adaptions by memphiz@xbmc.org*/
 
-#ifdef WIN32
 #ifndef win32_COMPAT_H_
 #define win32_COMPAT_H_
+
+#ifdef WIN32
 #define NO_IPv6 1
 
 #include <winsock2.h>
@@ -65,16 +66,22 @@ typedef int socklen_t;
 #define writev               win32_writev
 #define strncasecmp          _strnicmp
 #define strdup               _strdup
-#define dup2(x, y, z)        win32_dup2(x, y)
+#define dup2(x, y)           win32_dup2(x, y)
 #define poll(x, y, z)        win32_poll(x, y, z)
 #define inet_pton(x,y,z)     win32_inet_pton(x,y,z)
 #define sleep(x)             Sleep(x * 1000)
+#define getpid               GetCurrentProcessId
+
+#if defined(_MSC_VER) && _MSC_VER < 1900
 #define snprintf(a, b, c, ...) _snprintf_s(a, b, b, c, ## __VA_ARGS__)
+#endif
+
 int     win32_inet_pton(int af, const char * src, void * dst);
 int     win32_poll(struct pollfd *fds, unsigned int nfsd, int timeout);
 int     win32_gettimeofday(struct timeval *tv, struct timezone *tz);
 ssize_t win32_writev(int fd, const struct iovec *iov, int iovcnt);
 ssize_t win32_readv(int fd, const struct iovec *iov, int iovcnt);
+int     win32_dup2(int oldfd, int newfd);
 
 struct iovec {
     void *iov_base;
@@ -83,5 +90,5 @@ struct iovec {
 
 #define inline
 
-#endif//win32_COMPAT_H_
-#endif//WIN32
+#endif // WIN32
+#endif // win32_COMPAT_H_