osdep/io: add ftruncate for win32

Trivial wrapper around _chsize_s() to return -1 on errors always.
_chsize_s() returns errno value. At the same time errno is set to the
same value.

FILE_WRITE_DATA has to be added in append mode, because _chsize_s()
requires write permissions, not only append. We lose atomic append, but
we follow POSIX here, so that's fine, I guess.

osdep/io.c

@@ -369,8 +369,9 @@ int mp_open(const char *filename, int oflag, ...)
         FILE_SHARE_READ | FILE_SHARE_WRITE | FILE_SHARE_DELETE;
     // Setting FILE_APPEND_DATA and avoiding GENERIC_WRITE/FILE_WRITE_DATA
     // will make the file handle use atomic append behavior
+    // However to implement ftruncate we need FILE_WRITE_DATA
     static const DWORD append =
-        FILE_APPEND_DATA | FILE_WRITE_ATTRIBUTES | FILE_WRITE_EA;
+        FILE_APPEND_DATA | FILE_WRITE_ATTRIBUTES | FILE_WRITE_EA | FILE_WRITE_DATA;
 
     DWORD access = 0;
     DWORD disposition = 0;
@@ -709,6 +710,13 @@ off_t mp_lseek64(int fd, off_t offset, int whence)
     return _lseeki64(fd, offset, whence);
 }
 
+int mp_ftruncate64(int fd, off_t length)
+{
+    if (_chsize_s(fd, length) == 0)
+        return 0;
+    return -1;
+}
+
 _Thread_local
 static struct {
     DWORD errcode;

osdep/io.h

@@ -100,6 +100,7 @@ char *mp_to_utf8(void *talloc_ctx, const wchar_t *s);
 #include "dirent-win.h"
 #else
 #include <dirent.h>
+#include <unistd.h>
 #endif
 
 #ifdef _WIN32
@@ -133,6 +134,7 @@ char ***mp_penviron(void);
 #undef off_t
 #define off_t int64_t
 off_t mp_lseek64(int fd, off_t offset, int whence);
+int mp_ftruncate64(int fd, off_t length);
 void *mp_dlopen(const char *filename, int flag);
 void *mp_dlsym(void *handle, const char *symbol);
 char *mp_dlerror(void);
@@ -198,6 +200,9 @@ void mp_globfree(mp_glob_t *pglob);
 #undef lseek
 #define lseek(...) mp_lseek64(__VA_ARGS__)
 
+#undef ftruncate
+#define ftruncate(...) mp_ftruncate64(__VA_ARGS__)
+
 #define RTLD_NOW 0
 #define RTLD_LOCAL 0
 #define dlopen(fn,fg) mp_dlopen((fn), (fg))