Hi Pali,


On 7/30/21 2:05 PM, Pali Rohár wrote:

quoted

quoted

+
+int
+main(int argc, char *argv[])
+{
+#if !defined(TCGETS2) || !defined(TCSETS2) || !defined(BOTHER)
+    fprintf(stderr, "TCGETS2, TCSETS2 or BOTHER is unsupported\\n");
+    return 1;
+#else

Do we want the program to compile if those are unsupported?

My intention was to provide example which compiles fine on any Linux
architecture and in case of error it reports it at runtime.

On architectures where are TCGETS2/TCSETS2 ioctls unsupported, there are
still supported TCGETS/TCSETS ioctls. So proper Linux portable program
should fallback to TCGETS/TCSETS ioctls with Bnnn constants.

So for example setting baudrate to 115200 would be possible via
predefined constant B115200 in c_cflag member even when struct termios2
with c_ospeed is unsupported.

I just did not put this fallback into this example as it would be quite
loooong (as it is needed to add big switch for every Bnnn constant and
convert numeric value into Bnnn) and example show how to use
TCGETS2/TCSETS2 (not TCGETS/TCSETS).

Okay, I leave it up to you what you consider best to do :)

quoted

Maybe you can #error there and simplify the reader having to parse the
preprocessor directive mentally:

#if !defined...
# error ...
#endif

I know it's non-standard, but I think it's common enough so that we can use
it here.

#error is standard. It is already defined in C99 (section 6.10.5 Error
directive).

Ahh, it is #warning that is non-standard!  Thanks.  I forgot that.

quoted

quoted

+    struct termios2 tio2;
+    int fd, rc;
+
+    if (argc != 2 && argc != 3) {
+        fprintf(stderr, "Usage: %s device [new_baudrate]\\n", argv[0]);

We use \e for printing the escape character.  Not \\

Ok!

quoted

CC: Branden

See groff_man(7):
    Portability
        [...]

        Similar  caveats  apply  to escapes.  Some escape sequences
        are however required for correct typesetting  even  in  man
        pages and usually do not cause portability problems:

        [...]

        \e     Widely used in man pages to  represent  a  backslash
               output  glyph.  It works reliably as long as the .ec
               request is not used, which should  never  happen  in
               man pages, and it is slightly more portable than the
               more exact ‘\(rs’  (“reverse  solidus”)  escape  se‐
               quence.

quoted

+        return 1;
+    }
+
+    fd = open(argv[1], O_RDWR | O_NONBLOCK | O_NOCTTY);
+    if (fd < 0) {
+        perror("open");
+        return 1;

exit(EXIT_FAILURE);

quoted

+    }
+
+    rc = ioctl(fd, TCGETS2, &tio2);
+    if (rc) {
+        perror("TCGETS2");
+        close(fd);
+        return 1;

exit(3)

quoted

+    }
+
+    printf("%u\\n", tio2.c_ospeed);

\e

quoted

+
+    if (argc == 3) {
+        tio2.c_cflag &= ~CBAUD;
+        tio2.c_cflag |= BOTHER;
+        tio2.c_ospeed = tio2.c_ispeed = atoi(argv[2]);
+
+        rc = ioctl(fd, TCSETS2, &tio2);
+        if (rc) {
+            perror("TCSETS2");
+            close(fd);
+            return 1;

exit(3)

quoted

+        }
+    }
+
+    close(fd);
+    return 0;

exit(3)

Interesting... Do you prefer to use exit(EXIT_SUCCESS) instead of return 0?

I don't care in my own code.
I typically use return 0 at the end of main.
But the historical convention in manual pages is using exit(EXIT_SUCCESS),
so let's follow that :)


Tanks,

Alex


-- 
Alejandro Colomar
Linux man-pages comaintainer; https://www.kernel.org/doc/man-pages/
http://www.alejandro-colomar.es/