win32: handle /dev/zero and /dev/urandom in open and read functions

Currently /dev/zero is handled as a special case in dd.  Add hacks
to the open and read functions in mingw.c to handle the zero and
urandom devices.

- Opening /dev/zero or /dev/urandom actually opens the special
  Windows file 'nul' which behaves like /dev/null.  This allows
  manipulation of the file descriptor with things like seek and
  close

- When /dev/zero or /dev/urandom is opened the resulting file
  descriptor is stored and used to override the behaviour of read.

- No attempt is made to track duplicated file descriptors, so using
  these devices for redirections in the shell isn't going to work
  and won't be permitted.  (Could be, but won't.)

- Limited control of the special file descriptors is provided by
  allowing the internal variables to be changed.

- The numbers from /dev/urandom aren't very random.

1 files changed, 5 insertions, 0 deletions

diff --git a/include/mingw.h b/include/mingw.h
index a59ce6fc4..46be4dc23 100644
--- a/include/mingw.h
+++ b/include/mingw.h
@@ -395,6 +395,10 @@ int kill(pid_t pid, int sig);
 int link(const char *oldpath, const char *newpath);
 NOIMPL(mknod,const char *name UNUSED_PARAM, mode_t mode UNUSED_PARAM, dev_t device UNUSED_PARAM);
 int mingw_open (const char *filename, int oflags, ...);
+void mingw_read_zero(int fd);
+void mingw_read_random(int fd);
+ssize_t mingw_read(int fd, void *buf, size_t count);
+int mingw_close(int fd);
 int pipe(int filedes[2]);
 NOIMPL(readlink,const char *path UNUSED_PARAM, char *buf UNUSED_PARAM, size_t bufsiz UNUSED_PARAM);
 NOIMPL(setgid,gid_t gid UNUSED_PARAM);
@@ -418,6 +422,7 @@ int mingw_isatty(int fd);
 #define getcwd mingw_getcwd
 #define lchown chown
 #define open mingw_open
+#define close mingw_close
 #define unlink mingw_unlink
 #define rmdir mingw_rmdir
 #undef lseek