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To: Andrew Morton <akpm@osdl.org>
Cc: Zach Brown <zach.brown@oracle.com>, linux-kernel@vger.kernel.org
Subject: Re: [patch] call truncate_inode_pages in the DIO fallback to buffered I/O path
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From: Jeff Moyer <jmoyer@redhat.com>
Date: Wed, 04 Oct 2006 17:22:46 -0400
In-Reply-To: <x49ejtn7qfy.fsf@segfault.boston.devel.redhat.com> (Jeff Moyer's message of "Wed, 04 Oct 2006 16:53:53 -0400")
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==> Regarding Re: [patch] call truncate_inode_pages in the DIO fallback to buffered I/O path; Jeff Moyer <jmoyer@redhat.com> adds:
jmoyer> Again, sorry that I didn't include a better description.  I've
jmoyer> attached my reproducer to this message.

Oops, forgot to attach it.

-Jeff

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

int
make_sparse(const char *filename, off_t len)
{
	int fd;

	fd = open(filename, O_WRONLY | O_CREAT, 0644);
	if (fd < 0) {
		perror("open");
		return -1;
	}

	if (ftruncate(fd, 0) != 0) {
		perror("ftruncate");
		return -1;
	}
	if (ftruncate(fd, len) != 0) {
		perror("ftruncate");
		return -1;
	}

	close(fd);
	return 0;
}

int
main(int argc, char **argv)
{
	int fd, i, nr_pages, ret;
	off_t len;
	int page_size = getpagesize();
	char *buf;
	char *pattern;

	if (argc < 3) {
		printf("Usage: %s <filename> <size-in-megabytes>\n", argv[0]);
		exit(1);
	}

	/* convert length to megabytes */
	len = strtoul(argv[2], NULL, 10);
	len <<= 20;

	if (make_sparse(argv[1], len) < 0)
		exit(4);

	nr_pages = len / page_size;

	if ((ret = posix_memalign((void **)&buf, 1024, page_size)) != 0) {
		errno = ret;
		perror("posix_memalign");
		exit(2);
	}


	fd = open(argv[1], O_WRONLY | O_CREAT | O_DIRECT);
	if (fd < 0) {
		perror("open");
		exit(3);
	}

	memset(buf, 'b', page_size);
	for (i = 0; i < nr_pages; i++) {
		ret = write(fd, buf, page_size);
		if (ret < 0) {
			perror("write");
			exit(5);
		}
	}
	close(fd);

	/* now read the data back in and make sure it hit the disk! */
	pattern = malloc(page_size);
	if (!pattern) {
		perror("malloc");
		exit(1);
	}
	memset(pattern, 'b', page_size);

	fd = open(argv[1], O_RDONLY);
	if (fd < 0) {
		perror("open");
		exit(1);
	}

	while (i < len) {
		memset(buf, 0, sizeof(buf));
		ret = read(fd, buf, page_size);
		if (ret != page_size) {
			if (ret < 0)
				perror("read");
			else
				fprintf(stderr, "short read of %d\n", ret);
			exit(1);
		}
		if (memcmp(buf, pattern, page_size)) {
			fprintf(stderr, "Invalid Data!\n");
			exit(1);
		}
		i += page_size;
	}
	
	exit(0);
}