Re: zeroes read back more often than appended

[Pat LaVarre <p.lavarre@ieee.org>]

Specifically next I hope to show that appending nonzero bytes to
multiple open files reads back wrong.

Seemingly as yet I have some tupographical errors in the following.

With nonzero dd seek and SMP on and PREEMPT on in -test8, initially I
see:
198 whd: whd.c:45: main: Assertion `rc == width' failed.

Pat LaVarre

--- whd.c

#include <assert.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

static FILE * fi[1234];

int main(int argc, char * argv[]) // 0xFF600 0xC8
{
	int width;
	int height;
	int depth;
	char * chars;
	char nonzero;
	int h;
	int d;
	int rc;

	--argc; ++argv;
	assert(argc == 3);
	rc = sscanf(argv[0], "0x%X", &width);
	assert(rc == 1);
	rc = sscanf(argv[1], "0x%X", &height);
	assert(rc == 1);
	rc = sscanf(argv[1], "0x%X", &depth);
	assert(rc == 1);
	assert(depth < (sizeof fi / sizeof fi[0]));

	nonzero = '\xAA';
	chars = malloc(width);
	assert(chars != NULL);
	memset(&chars[0], nonzero, width);

	for (d = 0; d < depth; ++d) {
		char st[123];
		sprintf(&st[0], "whd%d.bin", d);
		fi[d] = fopen(&st[0], "wb");
		assert(fi[d] != NULL);
	}

	for (h = 0; h < height; ++h) {
		fprintf(stderr, "\r%d ", height - h - 1);
		for (d = 0; d < depth; ++d) {
			rc = fwrite(chars, 1, width, fi[d]);
			assert(rc == width);
		}
	}

	for (d = 0; d < depth; ++d) {
		rc = fclose(fi[d]);
		assert(rc == 0);
	}

	fprintf(stderr, "\n");

	for (d = 0; d < depth; ++d) {
		char st[123];
		sprintf(&st[0], "hexdump -C whd%d.bin | head -3", d);
		fprintf(stderr, "%s\n", st);
		(void) system(st);
	}

	return 0;
}

--- udfwhd

#!/bin/bash

uname -msr
pwd
rm dd.bin
cmd='dd if=/dev/zero of=dd.bin bs=1M seek=0 count=256'
cmd='dd if=/dev/zero of=dd.bin bs=1M seek=255 count=1'
echo "$cmd 2>/dev/null"
$cmd 2>/dev/null
ls -l dd.bin

sudo losetup /dev/loop0 dd.bin
sudo $1 2>&1 | head -1
sudo $1 /dev/loop0 >/dev/null

sudo mount /dev/loop0 /mnt/loop0
sudo chown `id -u`:`id -g` /mnt/loop0/.
dmesg >1.dmesg
cd /mnt/loop0
whd $2 $3 $4
cd -
dmesg >2.dmesg

diff -u 1.dmesg 2.dmesg | grep '^\+' | head -5
rm 1.dmesg 2.dmesg
sudo umount /mnt/loop0
sudo losetup -d /dev/loop0

---