fallocate VS ftruncate demo

gistfile1.c

#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <fcntl.h>

int main(int argc, char **argv)
{
	if (argc != 3) {
		printf("Usage: allocate <1:ftruncate, 2:fallocate> <size> \n");
		exit(1);
	}
	
	char cwd[255], path[255];
	if (!getcwd(cwd, sizeof(cwd))) {
		perror("Path too large");
		exit(1);
	}
	
	if (snprintf(path, 255, "%s/__allocate_chunk", cwd) >= 255) {
		perror("Path too large");
		exit(1);
	}
	
	printf("now opening %s\n", path);
	
	int fd;
	fd = open(path, O_RDWR | O_CREAT | O_TRUNC, 0666);
	
	if (fd == -1) {
		perror("Could not open the test file");
		exit(1);
	}
	
	int size = atoi(argv[2]);
	int mode = atoi(argv[1]);
	int ret;
	
	switch(mode) {
		case 1:
			printf("Using ftruncate \n");
			ret = ftruncate(fd, size);
		break;
		case 2:
			printf("Using fallocate\n");
			ret = posix_fallocate(fd, 0, size);
		break;
		default:
			fprintf(stderr, "Unkown mode : %d", mode);
			exit(-1);
	}
	
	if (ret) {
		perror("error writing");
		exit(1);
	}
	
	struct stat filestats;
	
	fstat(fd, &filestats);
	
	printf("Done !, st_blocks=%ld\n", filestats.st_blocks);
	
	close(fd);
	exit(0);
}