slcanpty: probe stdin capabilities at startup

/dev/null returns EOF therefore select() finishes immediately.
Now EOF is probed on start.

Other /dev/null as stdin workarounds:
- lscanpty ... < /dev/ptmx (dirty but works)
- cat </dev/null | slcanpty ... (doesn't work for me and even the patch
  is "disabled" then)

Signed-off-by: Janusz Uzycki <j.uzycki@elproma.com.pl>
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>

diff --git a/slcanpty.c b/slcanpty.c
index 8a11473a17328ea3e7ae08aa82caa72228bef7a6..2c1cabea262f2b80f10a40bd9cf912a7c03a2a7b 100644 (file)
--- a/slcanpty.c
+++ b/slcanpty.c
@@ -64,7 +64,7 @@ static int asc2nibble(char c)
 
 /* read data from pty, send CAN frames to CAN socket and answer commands */
 int pty2can(int pty, int socket, struct can_filter *fi,
-              int *is_open, int *tstamp)
+           int *is_open, int *tstamp)
 {
        int nbytes;
        char cmd;
@@ -386,6 +386,27 @@ int can2pty(int pty, int socket, int *tstamp)
        return 0;
 }
 
+int check_select_stdin(void)
+{
+       fd_set rdfs;
+       struct timeval timeout;
+       int ret;
+
+       FD_ZERO(&rdfs);
+       FD_SET(0, &rdfs);
+       timeout.tv_sec = 0;
+       timeout.tv_usec = 0;
+
+       ret = select(1, &rdfs, NULL, NULL, &timeout);
+
+       if (ret < 0)
+               return 0; /* not selectable */
+
+       if (ret > 0 && getchar() == EOF)
+               return 0; /* EOF, eg. /dev/null */
+
+       return 1;
+}
 
 int main(int argc, char **argv)
 {
@@ -395,6 +416,7 @@ int main(int argc, char **argv)
        struct sockaddr_can addr;
        struct termios topts;
        struct ifreq ifr;
+       int select_stdin = 0;
        int running = 1;
        int tstamp = 0;
        int is_open = 0;
@@ -416,6 +438,8 @@ int main(int argc, char **argv)
                return 1;
        }
 
+       select_stdin = check_select_stdin();
+
        /* open pty */
        p = open(argv[1], O_RDWR);
        if (p < 0) {
@@ -489,7 +513,10 @@ int main(int argc, char **argv)
        while (running) {
 
                FD_ZERO(&rdfs);
-               FD_SET(0, &rdfs);
+
+               if (select_stdin)
+                       FD_SET(0, &rdfs);
+
                FD_SET(p, &rdfs);
                FD_SET(s, &rdfs);