#include <unistd.h>#include <stdlib.h>#include <stdio.h>#include <fcntl.h>const char *test_file = "/tmp/test_lock";#define SIZE_TO_TRY 5void show_lock_info(struct flock *to_show);int main() {    int file_desc;    int res;    struct flock region_to_test;    int start_byte;            /* open a file descriptor */    file_desc = open(test_file, O_RDWR | O_CREAT, 0666);    if (!file_desc) {        fprintf(stderr, "Unable to open %s for read/write", test_file);        exit(EXIT_FAILURE);    }    for (start_byte = 0; start_byte < 99; start_byte += SIZE_TO_TRY) {            /* set up the region we wish to test */        region_to_test.l_type = F_WRLCK;        region_to_test.l_whence = SEEK_SET;        region_to_test.l_start = start_byte;        region_to_test.l_len = SIZE_TO_TRY;        region_to_test.l_pid = -1;             printf("Testing F_WRLCK on region from %d to %d\n",                start_byte, start_byte + SIZE_TO_TRY);                    /* now test the lock on the file */        res = fcntl(file_desc, F_GETLK, &region_to_test);        if (res == -1) {            fprintf(stderr, "F_GETLK failed\n");            exit(EXIT_FAILURE);        }        if (region_to_test.l_pid != -1) {            printf("Lock would fail. F_GETLK returned:\n");            show_lock_info(&region_to_test);        }        else {            printf("F_WRLCK - Lock would succeed\n");        }            /* now repeat the test with a shared (read) lock */                    /* set up the region we wish to test */        region_to_test.l_type = F_RDLCK;        region_to_test.l_whence = SEEK_SET;        region_to_test.l_start = start_byte;        region_to_test.l_len = SIZE_TO_TRY;        region_to_test.l_pid = -1;             printf("Testing F_RDLCK on region from %d to %d\n",                start_byte, start_byte + SIZE_TO_TRY);                    /* now test the lock on the file */        res = fcntl(file_desc, F_GETLK, &region_to_test);        if (res == -1) {            fprintf(stderr, "F_GETLK failed\n");            exit(EXIT_FAILURE);        }        if (region_to_test.l_pid != -1) {            printf("Lock would fail. F_GETLK returned:\n");            show_lock_info(&region_to_test);                    }        else {            printf("F_RDLCK - Lock would succeed\n");        }    } /* for */        close(file_desc);    exit(EXIT_SUCCESS);}void show_lock_info(struct flock *to_show) {    printf("\tl_type %d, ", to_show->l_type);    printf("l_whence %d, ", to_show->l_whence);    printf("l_start %d, ", (int)to_show->l_start);            printf("l_len %d, ", (int)to_show->l_len);    printf("l_pid %d\n", to_show->l_pid);}