Add per-platform file-open flags to std.os. Open buffers as desired in std._io.

src/lib/linux_os.rs

@@ -3,7 +3,7 @@ import _vec.vbuf;
 
 native mod libc = "libc.so.6" {
 
-  fn open(sbuf s, int flags) -> int;
+  fn open(sbuf s, int flags, uint mode) -> int;
   fn read(int fd, vbuf buf, uint count) -> int;
   fn write(int fd, vbuf buf, uint count) -> int;
   fn close(int fd) -> int;
@@ -17,3 +17,18 @@ native mod libc = "libc.so.6" {
   fn setenv(sbuf n, sbuf v, int overwrite) -> int;
   fn unsetenv(sbuf n) -> int;
 }
+
+mod libc_constants {
+  fn O_RDONLY() -> int { ret 0x0000; }
+  fn O_WRONLY() -> int { ret 0x0001; }
+  fn O_RDWR()   -> int { ret 0x0002; }
+  fn O_APPEND() -> int { ret 0x0400; }
+  fn O_CREAT()  -> int { ret 0x0040; }
+  fn O_EXCL()   -> int { ret 0x0080; }
+  fn O_TRUNC()  -> int { ret 0x0200; }
+  fn O_TEXT()   -> int { ret 0x0000; } // nonexistent in linux libc
+  fn O_BINARY() -> int { ret 0x0000; } // nonexistent in linux libc
+
+  fn S_IRUSR() -> uint { ret 0x0100u; }
+  fn S_IWUSR() -> uint { ret 0x0080u; }
+}