Hi all, I burn the iso again as Thomas suggested with this command:
> xorriso -as cdrecord \ > -v dev=/dev/sr0 blank=as_needed -eject padsize=300k \ > -sao debian-10.0.0-powerpc-NETINST-1.iso If I boot and try to mount the CDROM it fails again to mount the CDROM but I don't see the kernel messages as before. I mean, these ones: > > kernel: [timestamp] sr 1:0:0:0: [sr0] tag#0 Sense Key : Illegal Request > > kernel: [timestamp] sr 1:0:0:0: [sr0] tag#0 Add. Sense: Illegal mode for > > this track > > ... > > kernel: [timestamp] attempt to access beyond end device > > kernel: [timestamp] sr0: rw=0, want 640412, limit 640408 So Thomas was right about that one. I tried several ways of burning this image now, always failing to be mounted. I also tried an iBook G4, with the same result. So, I tried to do a sha512sum on the iso and it turned about the be incorrect. Sorry to bother you guys, I will download the iso again and try again to see if it mounts now, with a correct iso. Jeroen On Sun, 08 Nov 2020 15:10:55 +0100 "Thomas Schmitt" <scdbac...@gmx.net> wrote: > Hi, > > Jeroen Diederen wrote: > > kernel: [timestamp] sr 1:0:0:0: [sr0] tag#0 Sense Key : Illegal Request > > kernel: [timestamp] sr 1:0:0:0: [sr0] tag#0 Add. Sense: Illegal mode for > > this track > > ... > > kernel: [timestamp] attempt to access beyond end device > > kernel: [timestamp] sr0: rw=0, want 640412, limit 640408 > > This could be the TAO CD readahead bug with a drive which cooperates > badly with an obscure remedy in the kernel. > Preconditions for the bug are: > - CD-R or CD-RW medium, not DVD, not BD. > - Write type was Track-At-Once (which is default with cdrecord and wodim). > > The remedy, which only works beginning with the next read attempt, can be > seen in > https://github.com/torvalds/linux/blob/master/drivers/scsi/sr.c > under the false statement > * The SCSI specification allows for the value > * returned by READ CAPACITY to be up to 75 2K > * sectors past the last readable block. > If it works well, then it reduces the registered size of the medium > (ioctl(BLKGETSIZE), lsblk -o SIZE) by 4 KiB. It is know to work better > if the number of 2K blocks of the readable range is divisible by 2. > > In our case we have 160103 2K blocks and it looks like overcorrection: > > debian-10.0.0-powerpc-NETINST-1.iso of yesterday (2020110715225600) > has 327890944 bytes i.e. 640412 blocks of 512 bytes. > So above "want" is already beyond the end of the ISO but "limit" is inside. > "want" would match the initial perception mistake of the kernel, which > would be with the TAO bug 640416 or 640420 blocks, and an overshooting > correction to 640408 blocks. > The read access to the very end usually happens when software lookings > for a GPT backup block or for an UDF anchor block. > > > There are various rumors around this bug, but mine is provable and backed > by more optical drives than the others' together. >:] > > Normally it gets circumvented by a adding 300 KiB of padding at the end of > the CD track. If my theory is right, then no padding was added to this CD. > How exactly did you burn the it ? > > If the burn software offers write type Session-At-Once (SAO) then burn > again using this option. > > E.g. xorriso with explicit SAO (it uses it by default if possible) > and padding: > > xorriso -as cdrecord \ > -v dev=/dev/sr0 blank=as_needed -eject padsize=300k \ > -sao debian-10.0.0-powerpc-NETINST-1.iso > > The padding might lead to success even if my theory is wrong, because if > the drive would systematically underestimate SAO CDs, then the padding > would sacrifice itself to the mistake like a zinc anode does to salt water. > > So in case of success, it would be interesting to see whether a CD burnt > without option > padsize=300k > is mountable too, and whether a CD burnt by TAO without padding fails: > > xorriso -as cdrecord \ > -v dev=/dev/sr0 blank=as_needed -eject \ > -tao debian-10.0.0-powerpc-NETINST-1.iso > > ------------------------------------------------------------------------- > > If this all turns out to be really the old readahed bug, does anybody here > have enough reputation in linux-scsi to get a fix committed, which i have > ready as set of > [PATCH 0/3] Fix the old CD read-ahead bug for media with a single TAO track > [PATCH 1/3] cdrom: export cdrom_mmc3_profile() > [PATCH 2/3] sr: provide a test for readability of sectors as data blocks > [PATCH 3/3] sr: detect CD TAO Run-out blocks and correct device capacity > if needed > Currently based on 5.9-rc2. Works fine with various drives. > Lengthy cover letter and commit messages. Like this mail. Sorry for that. > > > Have a nice day :) > > Thomas > -- Jeroen Diederen <jjhdiede...@zonnet.nl>
