2.4.27rc2, DVD-RW support broke DVD-RAM writes

2.4.27rc2, DVD-RW support broke DVD-RAM writes

[Mathias Kretschmer]

Hi,

With 2.4.27rc2 (and I assume anything later than pre5 - that's when 
DVD-RW got added) DVD-RAMs have become read-only. Opening a DVD-RAM for 
writing results in "EROFS (Read-only file system)" (reported by 
'strace'. Let me know if I can provide any further info.
I'd be happy to test any fixes.

Also, any chance we get proper 'DVD-RAM is write-protected' support in 
2.4.x ? It'd be really nice if write()/open(O_WRONLY) would fail in 
those cases.

Tx,

Mathias

Re: 2.4.27rc2, DVD-RW support broke DVD-RAM writes

[Pat LaVarre]

 > http://marc.theaimsgroup.com/?t=109043580300002

Mathias K:

Hi.  Have you tried only PATAPI DVD-RAM drives?  Only via ide-cd.o, 
rather than via ide-scsi.o?

Me, as yet I have no PATAPI DVD-RAM, so instead I tried a USB DVD-RAM 
drive, specifically the "HL-DT-ST" "DVDRAM" "A100" drive.

Agreed, 2.4.27-rc4 fails to write.  But for me, 2.4.26 also fails to 
write.

For USB DVD-RAM in 2.4, I think the root evil is the dmesg complaint 
"kernel: sr0: scsi-1 drive", which in turn arises from the host 
substituting vendor-specific op x1A for MMC op x5A "MODE SENSE (10)".  
I'm guessing PATAPI DVD-RAM breaks over some other issue, found in the 
drivers/ide/ide-cd.c of ide-cd.o rather than in drivers/scsi/sr.c of 
ide-scsi.o.

Pat LaVarre
http://linux-pel.blog-city.com/read/754579.htm

Re: 2.4.27rc2, DVD-RW support broke DVD-RAM writes

[Pat LaVarre]

> what you see in 2.4.27-rc3 when you try:
> sudo blockdev --getro /dev/hd*

Sorry, never mind, I can now reproduce this effect myself, because 
Michael Tilelli kindly lent me a PATAPI DVD-RAM drive.

We must have an asymmetry in 2.4 drivers/ide/ide-cd.c vs. 
drivers/scsi/sr.c.  I see 2.4.26 work, but then 2.4.27-rc3 chokes:

$ uname -msr
Linux 2.4.27-rc4 i686
$
$ sudo rrd scan /dev/hdd
/dev/hdd is MATSHITA DVD-RAM A127 not RRD
$
$ sudo dd if=/dev/hdd bs=32K skip=0 count=1 | hexdump -C
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  
|................|
*
1+0 records in
1+0 records out
00008000
$ sudo dd of=/dev/hdd bs=32K skip=0 count=1 <xae.bin
dd: opening `/dev/hdd': Read-only file system
$ sudo blockdev --getro /dev/hdd
0
$

Pat LaVarre

Re: 2.4.27rc2, DVD-RW support broke DVD-RAM writes

[Pat LaVarre]

> > > let Pat fix it. Pat?
> ...
> must have an asymmetry in 2.4 drivers/ide/ide-cd.c vs. 
> drivers/scsi/sr.c.

A two-line workaround is the patch of my post:

Subject: [PATCH] DVD-RAM rewritable again
http://marc.theaimsgroup.com/?l=linux-scsi&m=109156820507518

That takes our 2.4 closer back to the bogus status quo ante for
CDROM_CAN(CDC_DVD_RAM) drives i.e. pass writes thru to all discs
inserted into such drives.

Pat LaVarre
http://linux-pel.blog-city.com/read/754579.htm