seek_hole.c

/* $Id: seek_hole.c,v 1.2 2012/05/26 04:50:22 kostik Exp kostik $ */

#include <sys/types.h>
#include <sys/stat.h>
#include <errno.h>
#include <fcntl.h>
#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

#define ERROR(str)							\
    fprintf(stderr, "%s: pos=%ju, errno=%d\n", str, (uintmax_t)pos, errno)

static int
reset_file(int fd)
{
	int ret;

	ret = ftruncate(fd, 0);
	if (ret < 0) {
		fprintf(stderr, "Truncate failed: %d\n", errno);
		return 1;
	}

	return 0;
}

static int block_size;

int
main(int argc, char **argv)
{
	char *buf;
	ssize_t bytes;
	off_t pos;
	int prealloc_is_hole = 0;
	int whole_file_is_data = 0;
	int ret;
	int i;
	int fd;

	fd = open("testfile", O_RDWR|O_CREAT|O_TRUNC, 0644);
	if (fd < 0) {
		fprintf(stderr, "Failed to open testfile: %s\n",
		    strerror(errno));
		return 1;
	}
	block_size = fpathconf(fd, _PC_MIN_HOLE_SIZE);
	if (block_size == -1) {
		fprintf(stderr, "Cannot get hole size: %s\n", strerror(errno));
		return (1);
	}
	buf = malloc(block_size * 4);

	/* Empty file */
	printf("Testing an empty file\n");
	pos = lseek(fd, 0, SEEK_DATA);
	if (pos != -1) {
		if (errno == EINVAL) {
			fprintf(stderr, "Kernel does not support seek "
				"hole/data\n");
			close(fd);
			return 1;
		}
		if (errno != ENXIO)
			ERROR("Seek data did not return a proper error");
		close(fd);
		return 1;
	}

	pos = lseek(fd, 0, SEEK_HOLE);
	if (pos != -1 && errno != ENXIO) {
		ERROR("Seek hole did not return a proper error");
		close(fd);
		return 1;
	}

	memset(buf, 'a', block_size * 4);
	/*
	 * All data file
	 */
	printf("Testing a normal data filled file\n");
	for (i = 0; i < 4; i++) {
		bytes = write(fd, buf, block_size);
		if (bytes < block_size) {
			fprintf(stderr, "Failed to write to testfile: %d\n",
				errno);
			close(fd);
			return 1;
		}
	}

	pos = lseek(fd, 0, SEEK_HOLE);
	if (pos != (block_size * 4) || pos == -1) {
		ERROR("Seek hole failed to dump us out at the end of the file");
		close(fd);
		return 1;
	}

	pos = lseek(fd, 0, SEEK_DATA);
	if (pos != 0) {
		ERROR("Seek data failed to dump us out at the beginning of the"
		      " file");
		close(fd);
		return 1;
	}

	/*
	 * File with a hole at the front and data at the end
	 */
	printf("Testing file with hole at the start and data in the rest\n");
	if (reset_file(fd)) {
		close(fd);
		return 1;
	}

	bytes = pwrite(fd, buf, block_size * 3, block_size);
	if (bytes < (block_size * 3)) {
		fprintf(stderr, "Failed to write to testfile\n");
		close(fd);
		return 1;
	}

	pos = lseek(fd, 0, SEEK_HOLE);
	if (pos != 0 && pos != (block_size * 4)) {
		ERROR("Seek hole failed to return 0");
		close(fd);
		return 1;
	} else if (pos == (block_size * 4)) {
		whole_file_is_data = 1;
		printf("Current file system views treats the entire file as "
		       "data\n");
	}

	pos = lseek(fd, 0, SEEK_DATA);
	if (pos != block_size && (pos != 0 && whole_file_is_data)) {
		if (whole_file_is_data)
			ERROR("Seek data failed to return 0");
		else
			ERROR("Seek data failed to return block_size");
		close(fd);
		return 1;
	}

	if (whole_file_is_data) {
		pos = lseek(fd, 1, SEEK_DATA);
		if (pos != -1 && errno != ENXIO) {
			ERROR("Seek data failed to return an error");
			close(fd);
			return 1;
		}
	}

#if 0
	/*
	 * File with a hole at the end and data at the beginning
	 */
	printf("Testing file with hole at the end and data at the beginning\n");
	if (reset_file(fd)) {
		close(fd);
		return 1;
	}

	ret = ftruncate(fd, block_size * 4);
	if (ret < 0) {
		fprintf(stderr, "Truncate failed: %d\n", errno);
		close(fd);
		return 1;
	}

	pwrite(fd, buf, block_size * 3, 0);
	if (bytes < (block_size * 3)) {
		fprintf(stderr, "Failed to write to testfile: %d\n", errno);
		close(fd);
		return 1;
	}

	pos = lseek(fd, 0, SEEK_HOLE);
	if (pos != (block_size * 3) && (pos != (block_size * 4) && whole_file_is_data)) {
		ERROR("Seeking hole didn't work right");
		close(fd);
		return 1;
	}

	if (whole_file_is_data) {
		pos = lseek(fd, pos, SEEK_HOLE);
		if (pos != -1 && errno != ENXIO) {
			ERROR("Seeking hole didn't return error");
			close(fd);
			return 1;
		}
		printf("No more tests to run since we treat the whole file as "
		       "data\n");
		goto out;
	}

	pos = lseek(fd, pos, SEEK_HOLE);
	if (pos != (block_size * 3)) {
		ERROR("Seek hole didn't return same position");
		close(fd);
		return 1;
	}

	pos = lseek(fd, pos+1, SEEK_HOLE);
	if (pos != (block_size * 4)) {
		ERROR("Seek hole didn't return the end of the file");
		close(fd);
		return 1;
	}

	pos = lseek(fd, pos, SEEK_DATA);
	if (pos != -1 && errno != ENXIO) {
		ERROR("Seek data didn't return ENXIO");
		close(fd);
		return 1;
	}
#endif

	/*
	 * Hole - Data - Hole - Data file
	 */
	printf("Testing file [Hole][Data][Hole][Data]\n");
	if (reset_file(fd)) {
		close(fd);
		return 1;
	}

	ret = ftruncate(fd, block_size * 4);
	if (ret < 0) {
		fprintf(stderr, "ftruncate failed: %d\n", errno);
		close(fd);
		return 1;
	}

	bytes = pwrite(fd, buf, block_size, block_size);
	if (bytes < block_size) {
		fprintf(stderr, "Failed to write: %d\n", errno);
		close(fd);
		return 1;
	}

	bytes = pwrite(fd, buf, block_size, block_size * 3);
	if (bytes < block_size) {
		fprintf(stderr, "Failed to write: %d\n", errno);
		close(fd);
		return 1;
	}

	pos = lseek(fd, 0, SEEK_DATA);
	if (pos != block_size) {
		ERROR("Seek data did not return block_size");
		close(fd);
		return 1;
	}

	pos = lseek(fd, pos, SEEK_HOLE);
	if (pos != (block_size * 2)) {
		ERROR("Seek hole did not return block_size*2");
		close(fd);
		return 1;
	}

	pos = lseek(fd, pos, SEEK_DATA);
	if (pos != (block_size * 3)) {
		ERROR("Seek data did not return block_size*3");
		close(fd);
		return 1;
	}
 out:
	close(fd);
	return 0;
}