Lock Testing Program

locktest.c

// JH Lock Test - 20110902
// I've used this in the past to debug locking issues (NFS)

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

char * filename;

int main(int argc, char* argv[]) {
    int lockrc;
    int fo;
    struct flock t_exlock,t_cklock;
    t_exlock.l_type = F_WRLCK;
    t_exlock.l_start = 0;
    t_exlock.l_len = 0;
    t_exlock.l_whence = SEEK_END;
    t_cklock.l_type = F_WRLCK;
    t_cklock.l_start = 0;
    t_cklock.l_len = 0;
    t_cklock.l_whence = SEEK_END;
    filename = argv[1];
    printf("lock tester - JH-20110902\n");
    if(argc < 2) {
        fprintf(stderr, "Usage: %s FILENAME\n", argv[0]);
        exit(22);
    }
    fo = open(filename, O_RDWR);

    printf("Getting lock on [%s] type [%d]...\n", filename, t_cklock.l_type);
    if(fcntl(fo,F_SETLK,&t_exlock) < 0) { // Try to grab exclusive lock first, if this fails then check the lock.
    printf("Wasn't able to get an exclusive lock, testing what lock exists...\n");
        lockrc = fcntl(fo, F_GETLK, &t_cklock);
    if(lockrc == 0) {
        if(t_cklock.l_type == F_UNLCK) {
        printf("File [%s] is not locked. If this is NFS, is nfslock running?\n", filename);
        } else {
        printf("Existing Lock details for %s.\n", filename);
        printf("\tLock PID: %d\n", t_cklock.l_pid);
        printf("\tLock Type: %d\n", t_cklock.l_type);
        }
    } else {
        perror("Error testing for lock. Did the file exist?");
    }
    } else {
      printf("Managed to get exlock on [%s] succesfully. No other lock exists.\n",filename);
    }
    printf("fcntl() finished...\n");
    close(fo);
}