/*
* mklock - create a secured lock entry with given data
* (c) 2003 - willy tarreau - willy@ant-computing.com
*
* You may use, copy and redistribute with no restriction. Use at your own
* risk, I will not be held responsible for any loss or damage.
*
* usage :
* # mklock <directory> [data]
*
* This will create a symlink under <directory>, either pointing to <data> if
* <data> is specified, or pointing to /proc/<getppid()> if no data is given.
* This way, the link will automatically be broken as soon as the father dies.
* The name of the link will be generated randomly until no conflict happens
* with an existing entry. The full pathname of the resulting link is returned
* to stdout so that a script can easily use it.
* This method ensures the use of a secure lock.
*
* Example :
* # file=`mklock /tmp $$`
*/
#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <errno.h>
#define writetxt(fd, text) write(fd, text, strlen(text))
#define LOCK_PREFIX ".lock."
#define PROC_PREFIX "/proc/"
#define MAX_PID_DIGITS 10 /* 10 digits do code a 32bit pid in decimal */
const char lock_prefix[] = LOCK_PREFIX;
const char proc_prefix[] = PROC_PREFIX;
/* writes <l> in at most 9 decimal digits to <to> */
void ultoa(char *to, unsigned long l) {
unsigned long div = 1000000000;
int zero = 1;
while (div > 0) {
*to = (l / div % 10) + '0';
div /= 10;
zero &= (*to == '0');
if (!zero)
to++;
}
*to = 0;
}
/* writes <l> as 8 hex digits to <to> */
void ultoh(char *to, unsigned long l) {
int shift = 32;
while ((shift -= 4) >= 0) {
int digit = (l >> shift) & 0xf;
if (digit > 9)
digit += 'A' - '9' - 1;
*to++ = digit + '0';
}
*to = 0;
}
void usage() {
writetxt(2, "Usage: mklock [ -d ] [ -p prefix ] <directory> [data]\n");
exit(1);
}
main(int argc, char **argv) {
char *text, *prefix;
char *directory;
char *fullname;
int len, num = 0, ret;
int use_dir = 0;
int plen;
prefix = lock_prefix;
argv++; argc--;
while (argc > 0 && **argv == '-') {
if (!strcmp(*argv, "-d")) {
use_dir = 1;
}
else if (!strcmp(*argv, "-p")) {
if (argc > 1) {
argv++; argc--;
prefix = argv[0];
}
else
usage();
}
argv++; argc--;
}
if (argc < 1)
usage();
plen = strlen(prefix);
directory = argv[0];
len = strlen(directory);
while (len > 0 && directory[len - 1] == '/')
directory[--len] = 0;
fullname = (char *)calloc(1, len + 1 + plen + 10);
memcpy(fullname, directory, len);
fullname[len++] = '/';
memcpy(fullname + len, prefix, plen + 1);
len += plen;
argv++; argc--;
if (argc > 0) /* use this arg as where the link points to */
text = argv[0];
else { /* point to /proc/<getppid()> */
text = (char *)malloc(strlen(PROC_PREFIX) + MAX_PID_DIGITS + 1);
memcpy(text, proc_prefix, strlen(PROC_PREFIX) + 1);
ultoa(text + strlen(PROC_PREFIX), getppid());
}
do {
/* try to create the entry with an increasing suffix until we succeed */
ultoh(fullname+len, num++);
if (use_dir)
ret = mkdir(fullname, 0700);
else
ret = symlink(text, fullname);
if (ret == 0) {
fullname[len + 8]='\n';
/* success, return the link or directory name */
write(1, fullname, len + 9);
return 0;
}
} while (errno == EEXIST);
/* other error, let's return 2 */
return 2;
}
