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printroot.c
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1990-07-19
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/* printroot - print root device on stdout Author: Bruce Evans */
/* This program figures out what the root device is by doing a stat on it, and
* then searching /dev until it finds an entry with the same device number.
* A typical use (probably the only use) is in /etc/rc for initializing
* /etc/mtab, as follows:
*
* /usr/bin/printroot >/etc/mtab
*
* 9 Dec 1989 - clean up for 1.5 - full prototypes (BDE)
* 15 October 1989 - avoid ACK cc bugs (BDE):
* - sizeof "foo" is 2 (from wrong type char *) instead of 4
* - char foo[10] = "bar"; allocates 4 bytes instead of 10
* 1 October 1989 - Minor changes by Andy Tanenbaum
*/
#include <sys/types.h>
#include <sys/dir.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <limits.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
static char DEV_PATH[] = "/dev/"; /* #define would step on sizeof bug */
static char MESSAGE[] = " is root device\n"; /* ditto */
#define UNKNOWN_DEV "/dev/unknown"
#define ROOT "/"
#ifdef __STDC__
static void done(char *name, int status);
#else
static void done();
#endif
int main(argc, argv)
int argc;
char **argv;
{
struct direct dir;
int fd;
struct stat filestat, rootstat;
static char namebuf[sizeof DEV_PATH + NAME_MAX];
if (stat(ROOT, &rootstat) == 0 && (fd = open(DEV_PATH, O_RDONLY)) >= 0) {
while (read(fd, (char *) &dir, sizeof dir) == sizeof dir) {
if (dir.d_ino == 0) continue;
strcpy(namebuf, DEV_PATH);
/* If next does not null-terminate, last in buf does it. */
strncat(namebuf, dir.d_name, NAME_MAX);
if (stat(namebuf, &filestat) != 0) continue;
if ((filestat.st_mode & S_IFMT) != S_IFBLK) continue;
if (filestat.st_rdev != rootstat.st_dev) continue;
done(namebuf, 0);
}
}
done(UNKNOWN_DEV, 1);
return 0; /* not reached */
}
static void done(name, status)
char *name;
int status;
{
write(1, name, strlen(name));
write(1, MESSAGE, sizeof MESSAGE - 1);
exit(status);
}