Re: zeroes read back more often than appended

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

Yes I can confirm.

Try appending nonzero to multiple files in a round robin sequence, and
udf.ko reads back zero in place of the nonzero written.  mkfs in place
of mkudffs reads back only the nonzero written.

CONFIG_SMP is not set.  CONFIG_PREEMPT is not set.  I did tell dd to
write all the backing store without skipping over any of it.

Changing those variables does fix the "width x height" test case of one
file, but not the "width x height x depth" test case of multiple files.

In particular I tried:

fswhd 0 768 mkudffs 0xFF600 0xC8 0x3
fswhd 0 768 mkudffs 0xFF600 0xC8 0x1
fswhd 0 768 mkudffs 0xFF600 0xC8 0x2

That sequence actually took down my kernel once, but for me that trouble
did not repeat.  I do not yet know where to go to begin learning how to
see the dmesg leading up to an oops.  oops kill my remote ssh.

Pat LaVarre

P.S. tty logs follow.  Two files with mkudffs, reads zeroes from both
files ouch.  One file with mkudffs, ok because of CONFIG = PREEMPT =
off.  Two files with mkfs in place of mkudffs, ok.

$
$ cd /mnt/hda11
$
$ fswhd 0 768 mkudffs 0xFF600 0xC8 0x2
Linux 2.6.0.8-udf i686
/mnt/hda11
dd if=/dev/zero of=dd.bin bs=1M seek=0 count=768 2>/dev/null
-rw-rw-r--    1 pat      pat      805306368 Oct 21 11:49 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  |................|
*
06fbe000  00 00 00 00 00 00 00 00  aa aa aa aa aa aa aa aa  |................|
hexdump -C whd1.bin | head -3
00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
*
06ebb000  00 00 00 00 00 00 00 00  aa aa aa aa aa aa aa aa  |................|
+++ 2.dmesg     2003-10-21 11:50:13.486227568 -0600
+ already set
+UDF-fs DEBUG fs/udf/balloc.c:192:udf_bitmap_free_blocks: bit 15865 already set
+UDF-fs DEBUG fs/udf/balloc.c:193:udf_bitmap_free_blocks: byte= 2
+UDF-fs DEBUG fs/udf/balloc.c:192:udf_bitmap_free_blocks: bit 15865 already set
$
$ fswhd 0 768 mkudffs 0xFF600 0xC8 0x1
Linux 2.6.0.8-udf i686
/mnt/hda11
dd if=/dev/zero of=dd.bin bs=1M seek=0 count=768 2>/dev/null
-rw-rw-r--    1 pat      pat      805306368 Oct 21 11:46 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  |................|
*
0c783000
$
$ fswhd 0 768 mkfs 0xFF600 0xC8 0x2
Linux 2.6.0.8-udf i686
/mnt/hda11
dd if=/dev/zero of=dd.bin bs=1M seek=0 count=768 2>/dev/null
-rw-rw-r--    1 pat      pat      805306368 Oct 21 11:52 dd.bin
Usage: mkfs [-V] [-t fstype] [fs-options] device [size]
mke2fs 1.32 (09-Nov-2002)
0
hexdump -C whd0.bin | head -3
00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
*
0c783000
hexdump -C whd1.bin | head -3
00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
*
0c783000
$