Re: zeroes read back more often than appended

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

Yes indeed, again I see udf reading of more zeroes than appended, if I
try 2.6.0-test8 with SMP, with PREEMPT, on seek-write backing store, via
the trivially revised whd.c and fswhd script quoted as a patch below.

Why so carefully do nothing different in a more complex way?

So that now more easily we can try changing those variables.  In
particular, I hope to show failures without SMP, without PREEMPT, on
preallotted backing store, in such tests as:

fswhd 0 768 mkudffs 0xFF600 0xC8 0x3

Pat LaVarre

diff -Nur o/tty.txt bin/tty.txt
--- o/tty.txt	1969-12-31 17:00:00.000000000 -0700
+++ bin/tty.txt	2003-10-21 09:20:38.113900136 -0600
@@ -0,0 +1,18 @@
+$
+$ cd /mnt/hda11; fswhd 255 1 mkudffs 0xFF600 0xC8 0x1
+Linux 2.6.0-test8 i686
+/mnt/hda11
+dd if=/dev/zero of=dd.bin bs=1M seek=255 count=1 2>/dev/null
+-rw-rw-r--    1 pat      pat      268435456 Oct 21 09:18 dd.bin
+mkudffs 1.0.0b2 for UDF FS 1.0.0-cvs, 2002/02/09
+0
+hexdump -C whd0.bin | head -3
+00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
+*
+034cd000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
++++ 2.dmesg     2003-10-21 09:19:06.301857688 -0600
++fffff
++UDF-fs DEBUG fs/udf/balloc.c:192:udf_bitmap_free_blocks: bit 2951 already set
++UDF-fs DEBUG fs/udf/balloc.c:193:udf_bitmap_free_blocks: byte=ffffff80
++UDF-fs DEBUG fs/udf/balloc.c:192:udf_bitmap_free_blocks: bit 2951 already set
+$
diff -Nur o/whd.c bin/whd.c
--- o/whd.c	1969-12-31 17:00:00.000000000 -0700
+++ bin/whd.c	2003-10-21 08:45:30.000000000 -0600
@@ -0,0 +1,67 @@
+#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[2], "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]);
+			if (rc != width) {
+				perror("fwrite");
+				exit(-__LINE__);
+			}
+		}
+	}
+
+	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;
+}
diff -Nur o/fswhd bin/fswhd
--- o/fswhd	1969-12-31 17:00:00.000000000 -0700
+++ bin/fswhd	2003-10-21 09:15:34.103116800 -0600
@@ -0,0 +1,26 @@
+#!/bin/bash
+
+uname -msr
+pwd
+rm dd.bin
+cmd="dd if=/dev/zero of=dd.bin bs=1M seek=$1 count=$2"
+echo "$cmd 2>/dev/null"
+$cmd 2>/dev/null
+ls -l dd.bin
+
+sudo losetup /dev/loop0 dd.bin
+sudo $3 2>&1 | head -1
+sudo $3 /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 $4 $5 $6
+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