There are a lot of reports like this in the forums. I haven't yet found
an answer.
As with others, this started with a system upgrade, in my case from
hardy to intrepid. I'm running kernel 2.6.27-11-generic. I'm getting
similar, but not identical results to most other people, and maybe this
might throw some light on things.
I've had much the same results whether it's with a burnt CD or a store
bought DVD.
my lshw output for the CDROM:
*-cdrom
description: DVD-RAM writer
product: DVD-RAM UJ-841S
vendor: MATSHITA
physical id: 1
bus info: s...@1:0.0.0
logical name: /dev/cdrom
logical name: /dev/cdrw
logical name: /dev/dvd
logical name: /dev/dvdrw
logical name: /dev/scd0
logical name: /dev/sr0
logical name: /media/cdrom0
version: 1.50
capabilities: removable audio cd-r cd-rw dvd dvd-r dvd-ram
configuration: ansiversion=5 mount.fstype=iso9660
mount.options=ro,nosuid,nodev,noexec state=mounted status=ready
*-medium
physical id: 0
logical name: /dev/cdrom
logical name: /media/cdrom0
configuration: mount.fstype=iso9660
mount.options=ro,nosuid,nodev,noexec state=mounted
Currently there's a movie DVD in the drive. I've had much the same
results though whether reading a burnt data CD or a store bought movie
DVD.
In dmesg I see lots of:
[244935.679920] attempt to access beyond end of device
[244935.679923] sr0: rw=0, want=199360, limit=6124
[244935.804247] attempt to access beyond end of device
[244935.804269] sr0: rw=0, want=64192, limit=6124
[244935.804279] attempt to access beyond end of device
[244935.804288] sr0: rw=0, want=64196, limit=6124
Notably many other reports seem to say 'limit=4', wheras my limit is
larger (6124), but that number is consistent for me across different CD
and DVD discs. Probably as a result of this larger limit, while many
people cannot mount the disc, I can mount it and read the first part of
the disk, including some directories and files. I can Identify the file
that crosses the limit of the detected device size - I can read the
first part of the file, and not the latter part. When reading
sequentially, it goes along OK for a bit, then fails and dmesg reports:
Apr 19 23:08:56 andrew-laptop kernel: [246230.680122] attempt to access beyond
end of device
Apr 19 23:08:56 andrew-laptop kernel: [246230.680140] sr0: rw=0, want=6128,
limit=6124
Apr 19 23:08:56 andrew-laptop kernel: [246230.680148] Buffer I/O error on
device sr0, logical block 1531
Apr 19 23:08:56 andrew-laptop kernel: [246230.683944] attempt to access beyond
end of device
Apr 19 23:08:56 andrew-laptop kernel: [246230.683956] sr0: rw=0, want=6132,
limit=6124
Apr 19 23:08:56 andrew-laptop kernel: [246230.683963] Buffer I/O error on
device sr0, logical block 1532
Apr 19 23:08:56 andrew-laptop kernel: [246230.687969] attempt to access beyond
end of device
Apr 19 23:08:56 andrew-laptop kernel: [246230.687980] sr0: rw=0, want=6136,
limit=6124
...etc.
Trying to read other files that start later on the disk fails entirely,
with the now familiar error pattern.
It appears that the information on the size of the device is being
detected incorrectly. The specific bug might be different in my case,
but the effects that flow from this are presumably much the same. When
the supposed size is 4 as in most people's reports, they can't read
enough to mount the file system.
and...@andrew-laptop$ cat /dev/scd0 | wc -c
3135488
Which is exactly 6124*512. Presumably that 'limit=6124' in my logs is
expressed in 512 byte blocks. No error in the shell or in my kernel
logs from this test. I had thought it might go until it hit its limit
and then start producing errors, but instead it just stops reading the
device at the point where the supposed size limit is hit.
df reports the size of the filesystem as being larger:
and...@andrew-laptop$ df
Filesystem 1K-blocks Used Available Use% Mounted on
...
/dev/scd0 840704 840704 0 100% /media/cdrom0
Presumably that figure is the size of the file system as opposed to the
device, and the size is stored in some sort of metadata within the
filesystem itself. I don't think there is any problem in the working of
the file system except that problems with reading the underlying device
prevent access to most of it.
--
mounting dvd says: block device is write protected
https://bugs.launchpad.net/bugs/244445
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