/*
** This file implements a simple command-line utility that shows all of the
** Posix Advisory Locks on a file.
**
** Usage:
**
** showlocks FILENAME
**
** To compile: gcc -o showlocks showlocks.c
*/
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <stdlib.h>
#include <string.h>
/* This utility only looks for locks in the first 2 billion bytes */
#define MX_LCK 2147483647
/*
** Print all locks on the inode of "fd" that occur in between
** lwr and upr, inclusive.
*/
static int showLocksInRange(int fd, off_t lwr, off_t upr){
int cnt = 0;
struct flock x;
x.l_type = F_WRLCK;
x.l_whence = SEEK_SET;
x.l_start = lwr;
x.l_len = upr-lwr;
fcntl(fd, F_GETLK, &x);
if( x.l_type==F_UNLCK ) return 0;
printf("start: %-12d len: %-5d pid: %-5d type: %s\n",
(int)x.l_start, (int)x.l_len,
x.l_pid, x.l_type==F_WRLCK ? "WRLCK" : "RDLCK");
cnt++;
if( x.l_start>lwr ){
cnt += showLocksInRange(fd, lwr, x.l_start-1);
}
if( x.l_start+x.l_len<upr ){
cnt += showLocksInRange(fd, x.l_start+x.l_len+1, upr);
}
return cnt;
}
int main(int argc, char **argv){
int fd;
int cnt;
if( argc!=2 ){
fprintf(stderr, "Usage: %s FILENAME\n", argv[0]);
return 1;
}
fd = open(argv[1], O_RDWR, 0);
if( fd<0 ){
fprintf(stderr, "%s: cannot open %s\n", argv[0], argv[1]);
return 1;
}
cnt = showLocksInRange(fd, 0, MX_LCK);
if( cnt==0 ) printf("no locks\n");
close(fd);
return 0;
}