Re: What's in my kernel?

[Jyan-Min Fang]

On Fri, 8 May 1998, Michael Jinks wrote:

> Sometimes when I'm doing lots of reconfiguration on several machines, or
> if it's been a while since I've tinkered with a particular box, it can
> be easy to forget how a particular machine's kernel was configured.  Is
> there a way to get a kernel to spit out something that vaguely resembles
> the configuration options I gave it at compile time?
> 
> Of course I could just keep better records, but that doesn't help me
> much with regard to past sins. . .

Dave Wreski once posted a program on this list which basically let you
look into a kernel what is in it. compile the program and run the follwing
command will tell you the Linux version. just grep whatever configuration
you want to know if your specific kernel has it or not.

a.out /boot/zImage.2.1.42 | gzip -d | strings -a | grep '^Linux version'

Jyan-Min Fang

"Today, I consider myself the luckiest man on the face of the earth"
--- Lou Gehrig --- Go, Yankees!

#include <stdlib.h>
#include <stdio.h>
#include <fcntl.h>

/*
# Gzip
0       string          \037\213        gzip compressed data
>2      byte            8               - deflate method
>3      byte            &0x1            , ascii
>3      byte            &0x2            , continuation
>3      byte            &0x4            , extra field
>3      byte            &0x8            , original file name
>3      byte            &0x10           , comment
>3      byte            &0x20           , encrypted
>8      byte            2               , max compression
>8      byte            4               , max speed
*/

#define BSIZE 4096
#define C1 037
#define C2 0213
#define C3 8

main(int argc, char **argv)
{
        unsigned char *bbuf;
        int bc;
        int ifd = 0;
        int ofd = 1;

        if (argc > 3) {
                fprintf(stderr, "usage: breakzi [in-file [out-file]]\n");
                exit(1);
        }
        if (argc > 1) {
          if ((ifd = open(argv[1], O_RDONLY)) < 0) {
                        perror(argv[1]);
                        exit(1);
          }
        }
        if (argc > 2) {
          if ((ofd = open(argv[2], O_WRONLY | O_CREAT, 0755)) < 0) {
                        perror(argv[2]);
                        exit(1);
          }
        }
        if ((bbuf = (char *)malloc(BSIZE)) < 0) {
                perror("bbuf");
                exit(1);
        }
        while (1) {
                readbyt(ifd, bbuf + 0);
                if (bbuf[0] != C1) {
                        continue;
                }
        overlap:
                readbyt(ifd, bbuf + 1);
                if (bbuf[1] != C2) {
                  if (bbuf[1] == C1) {
                                bbuf[0] = C1;
                                goto overlap;
                  }
                        continue;
                }
                readbyt(ifd, bbuf + 2);
                if (bbuf[2] != C3) {
                  if (bbuf[2] == C1) {
                                bbuf[0] = C1;
                                goto overlap;
                  }
                        continue;
                }
                break;
        }
        write(ofd, bbuf, 3);
        while (bc = read(ifd, bbuf, BSIZE)) {
                write(ofd, bbuf, bc);
        }
}

readbyt(int ifd, char *buf)
{
        int bc;

        if ((bc = read(ifd, buf, 1)) != 1) {
                fprintf(stderr, "EOF encountered before header\n");
                exit(1);
        }
}