Re: zeroes read back more often than appended

[Ben Fennema <bfennema@falcon.csc.calpoly.edu>]

I can't repeat this on 2.4 or 2.6.0-test6 non-smp.

I'll see if I can figure out whats going on in 2.6.0-test6-smp.

Somehow unrecorded block(s) are getting inserted in the data.

Ben

On Tue, Oct 07, 2003 at 01:02:21PM -0600, Pat LaVarre wrote:
> Maybe I should have cc'ed linux-fsdevel@vger.kernel.org when I launched
> this thread in linux_udf@hpesjro.fc.hp.com ...
> 
> -----Forwarded Message-----
> 
> Subject: zeroes read back more often than appended
> Date: 06 Oct 2003 21:54:15 -0600
> To: linux_udf@hpesjro.fc.hp.com
> 
> Is it legit to combine mkudffs 1.0.0b2 with linux-2.6.0-test6?
> 
> And to run mkudffs on top of a loop device?
> 
> I ask because:
> 
> I wrote the following short programs (a bash script and a C routine) to
> fopen, iterate "height" times to fwrite a "width" of bytes once or
> repeatedly, and fclose.
> 
> With mkfs and ext3, I see this trivial code reliably produces expected
> results i.e. a file full of '\xAA' e.g.
> 
> 00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
> *
> 00fffff0  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa     |...............|
> 
> With linux-2.6.0-test6 mkudffs and udf.ko of 1 GiB loop device, I see
> this trivial code reliably produces wrong results for certain small
> width and height combinations, such as:
> 
> udfwh mkudffs 0xFFFF 0xC00
> udfwh mkudffs 0xFFFFFF 0xB
> udfwh mkudffs 0xFFFFFFF 0x1
> udfwh mkudffs 0x7800000 0x1
> 
> With mkudffs, my results grow indeterminate below somewhere near the
> 0x7800000 boundary (120 MiB).  0x7400000 often fails.  My logs tell me
> 0x7298000 once failed for me, but I can't easily repeat that result.
> 
> My wrong results have lots of zeroes in place of the data written e.g.
> 
> hexdump -C wh.bin | head -3
> 00000000  aa aa aa aa aa aa aa aa  aa aa aa aa aa aa aa aa  |................|
> *
> 0375e000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
> 
> Every time I've looked, the zeroes appear aligned to at least 2 KiB
> boundaries.
> 
> Explanations, anyone?
> 
> Pat LaVarre
> 
> /// udfwh
> 
> #!/bin/bash -x
> 
> rm dd.bin
> dd if=/dev/zero of=dd.bin bs=1M seek=1023 count=1
> ls -l dd.bin
> sudo losetup /dev/loop0 dd.bin
> sudo $1 2>&1 | head -1
> sudo $1 /dev/loop0
> sudo mount /dev/loop0 /mnt/loop0
> sudo chown `id -u`:`id -g` /mnt/loop0/.
> cd /mnt/loop0
> time wh $2 $3
> cd -
> sudo umount /mnt/loop0
> sudo losetup -d /dev/loop0
> 
> /// wh.c
> 
> #include <assert.h>
> #include <stdio.h>
> #include <stdlib.h>
> #include <string.h>
> 
> int main(int argc, char * argv[]) // 0xFF600 0xC8
> {
> 	int width;
> 	int height;
> 	char * chars;
> 	char nonzero;
> 	FILE * fi;
> 	int i;
> 	int rc;
> 	char const * st;
> 
> 	--argc; ++argv;
> 	assert(argc == 2);
> 	rc = sscanf(argv[0], "0x%X", &width);
> 	assert(rc == 1);
> 	rc = sscanf(argv[1], "0x%X", &height);
> 	assert(rc == 1);
> 
> 	nonzero = '\xAA';
> 	chars = malloc(width);
> 	assert(chars != NULL);
> 	memset(&chars[0], nonzero, width);
> 
> 	fi = fopen("wh.bin", "wb");
> 	assert(fi != NULL);
> 	for (i = 0; i < height; ++i) {
> 		fprintf(stderr, "\r%d ", height - i - 1);
> 		rc = fwrite(chars, 1, width, fi);
> 		assert(rc == width);
> 	}
> 	rc = fclose(fi);
> 	assert(rc == 0);
> 	fprintf(stderr, "\n");
> 
> 	st = "hexdump -C wh.bin | head -3";
> 	fprintf(stderr, "%s\n", st);
> 	(void) system(st);
> 
> 	return 0;
> }
> 
> /// dmesg (boring, I think?)
> 
> > UDF-fs DEBUG fs/udf/lowlevel.c:65:udf_get_last_session: CDROMMULTISESSION not supported: rc=-22
> > UDF-fs DEBUG fs/udf/super.c:1471:udf_fill_super: Multi-session=0
> > UDF-fs DEBUG fs/udf/super.c:459:udf_vrs: Starting at sector 16 (2048 byte sectors)
> > UDF-fs DEBUG fs/udf/super.c:802:udf_load_pvoldesc: recording time 1065498482/249678, 2003/10/06 21:48 (1e98)
> > UDF-fs DEBUG fs/udf/super.c:813:udf_load_pvoldesc: volIdent[] = 'LinuxUDF'
> > UDF-fs DEBUG fs/udf/super.c:820:udf_load_pvoldesc: volSetIdent[] = '3f823772LinuxUDF'
> > UDF-fs DEBUG fs/udf/super.c:1012:udf_load_logicalvol: Partition (0:0) type 1 on volume 1
> > UDF-fs DEBUG fs/udf/super.c:1022:udf_load_logicalvol: FileSet found in LogicalVolDesc at block=32, partition=0
> > UDF-fs DEBUG fs/udf/super.c:850:udf_load_partdesc: Searching map: (0 == 0)
> > UDF-fs DEBUG fs/udf/super.c:891:udf_load_partdesc: unallocSpaceBitmap (part 0) @ 0
> > UDF-fs DEBUG fs/udf/super.c:932:udf_load_partdesc: Partition (0:0 type 1511) starts at physical 274, block length 523757
> > UDF-fs DEBUG fs/udf/super.c:1265:udf_load_partition: Using anchor in block 256
> > UDF-fs DEBUG fs/udf/super.c:1498:udf_fill_super: Lastblock=0
> > UDF-fs DEBUG fs/udf/super.c:774:udf_find_fileset: Fileset at block=32, partition=0
> > UDF-fs DEBUG fs/udf/super.c:836:udf_load_fileset: Rootdir at block=34, partition=0
> > UDF-fs INFO UDF 0.9.7 (2002/11/15) Mounting volume 'LinuxUDF', timestamp 2003/10/06 21:48 (1e98)