Help
hi I have been reading the Linux Device Drivers 3 book.
In Chapter 4 on debugging an example program for changing console for printk was given.
but it is not executing in my terminal what could be the reason? I have given the source code also.
Also when I googled for the TIOCLINUX command I was able find only 10 subcommands for it. what is the subcommand 11 doing in the code? Please direct me to any article or links or guide me.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <errno.h>
#include <unistd.h>
#include <sys/ioctl.h>
int main(int argc, char **argv)
{
char bytes[2] = {11,0}; /* 11 is the TIOCLINUX cmd number */
if (argc==2) bytes[1] = atoi(argv[1]); /* the chosen console */
else {
fprintf(stderr, "%s: need a single arg\n",argv[0]); exit(1);
}
if (ioctl(STDIN_FILENO, TIOCLINUX, bytes)<0) { /* use stdin */
fprintf(stderr,"%s: ioctl(stdin, TIOCLINUX): %s\n",
argv[0], strerror(errno));
exit(1);
}
exit(0);
}
Thank you
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usage of ioctl command TIOCLINUX1 Reply
Hi,
I passed your message on to the authors, and one of them replied with the following message. I hope that helps, Chris Olson O'Reilly Book Support ------ > In Chapter 4 on debugging an example program for changing console > for printk was given. but it is not executing in my terminal what > could be the reason? It must be executed in a linux terminal (text login on vga, or equivalent on non-pc platforms). I'm now running the "setconsole" program from our misc-progs directory. From a graphical terminal, it doesn't work: ostro% env | grep TERM= TERM=xterm ostro% ./setconsole 2 ./setconsole: ioctl(stdin, TIOCLINUX): Invalid argument And this is from a text login (control-alt-F2) in the same host: ostro% env | grep TERM= TERM=linux ostro% ./setconsole 2 ./setconsole: ioctl(stdin, TIOCLINUX): Operation not permitted ostro% sudo ./setconsole 2 ostro% > Also when I googled for the TIOCLINUX command I was able find only > 10 subcommands for it. what is the subcommand 11 doing in the code? > Please direct me to any article or links or guide me. You shouldn't google when you have the source code. In recent kernels the implementation is the function tioclinux() in ./drivers/tty/vt/vt.c (drivers/tty/vt/vt_ioctl.c implements ioctl and calls it). The implementation now uses symbolic names rather than numbers, and 11 is TIOCL_SETKMSGREDIRECT (defined in include/linux/tiocl.h): #define TIOCL_SETKMSGREDIRECT 11 /* restrict kernel messages to a vt */ And it works as advertised. Hope this helps /alessandro |
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