[aclug-L] Re: Serial port logging and redirection?

[Tom Hull <thull@xxxxxxxxxxx>]

Cheez-Czar wrote:
> 
> not being the most knowledgeable about devices, but with the idea that
> everything is a file, here is my idea
> 
> cat /dev/ttyS0 tee log > /dev/ttyS1

Of course, Clint meant:

  cat /dev/ttyS0 | tee log > /dev/ttyS1

The main problem with this is that tee(1) usually buffers its output (especially
to log), which means that data can get stuck inside tee's own buffers.

The script(1) program may work better in some cases (e.g., logging a telnet
session).

> On Mon, 23 Jul 2001, james l wrote:
> 
> >
> > is there some way to redirect input from say ttyS0 to both, a log file and
> > ttyS1 under linux? Aside from writing my own program, is there an easy way 
> > to
> > do this?

It's pretty close to trivial to write such a program -- just use 
read(2)/write(2).
Where:

    #define BUFMAX 4096  /* size of buffer to use, multiple of block size,
                            and <= maximum pipe buffer */
    char buf[BUFMAX];    /* buffer to use */
    int in_fd;           /* input file descriptor */
    int out_fds[];       /* output file descriptors */
    int i, nfd;          /* number of output file descriptors */
    size_t sz;           /* read(2) size */

The basic loop is:

    while ((sz = read(in_fd, buf, BUFMAX)) != (size_t) -1) {
        for (i = 0; i < nfd; i++) {
            write(out_fds[i], buf, sz);
        }
    }

Most likely, someone else has indeed written this program. Question is, how long
does it take to find it?

> > James L

-- 
/*
 *  Tom Hull * thull at kscable.com * http://www.ocston.org/~thull/
 */
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