different md5sums for files on /dev/cdrom

matousu at volny.cz matousu at volny.cz
Tue Mar 29 13:08:35 UTC 2005

I have encountered strange problem while reading my files
from CDROM. I am still troubleshooting this, so I apreciate
any help or notice to the problem I am describing below.

ASUS Pundit-R with Intel Prescott, Seagate ST3200822AS as hdc and
hda: ATAPI 40X DVD-ROM DVD-R CD-R/RW drive, 2048kB Cache, UDMA(33)

# uname -a
Linux pundit 2.6.10-1.741_FC3smp #1 SMP Thu Jan 13 16:53:16 EST
2005 i686 i686 i386 GNU/Linux
W2k installed on another partition.

I have cdrom A with a file, let say the file is named
file.cdrom-fc3, when mounted on fc3 linux.

On fc3 linux hdc6 I have file, let say file.w2k-to-fc3, which I
have previously read from cdrom A in Windows 2k and saved on shared
vfat and transfered to hdc6 after my fc3 linux boot. There is
nothing wrong with this file.

I have another linux on another machine, dell latitude with RH9 and
kernel 2.4.20.
Let say the file on cdrom A When I mount the cdrom in this linuxbox
become file.rh9

So now we have three files, all of them should have the same
md5sum, as the files are based on the same source,
and here they are:

0fed8b1345de558c18c5c9fa164b192a file.w2k-to-fc3 ---> OK
a1a4a1174be8579bee5c83caa5f696aa file.cdrom-fc3 !!!!! BAD
0fed8b1345de558c18c5c9fa164b192a file.rh9 ---> OK

So, the fc3 kernel driver handling the cdrom badly affects the
files. This is valid for any cdrom and any file.
The main efect is that mpeg or jpeg files are not or are badly
readable in fc3.
For instance mplayer gives messages like
[msmpeg4 @ 0x84e4bc8]Error at MB: 644
[msmpeg4 @ 0x84e4bc8]concealing 2147483647 errors.
with artefacts during the playback.
But the sideefect within the app is not important now.

I have disabled selinux and the behavior of jpeg files is better
now, I can read most of them, but still not OK, as visible also
from md5sums.

I can say, the cdrom drive is OK because it works well in w2k.
Also the file on cdrom is OK and healthy. It works in another OSes.

So I am suspecting these systems:
o kernel driver
o cdrom drive hdparameters - I am using default fc3 settings
o some another part of kernel sitting over devices, like selinux ?

I realy need to solve this so I apreciate _ANY_ info.
At least, if i write to wrong list, send me the email to people
which are able to help to find the reason of this problem, and
advice a solution.

Thanks in advance,

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