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SubjectRe: Linux 2.4.18: short dd read from IDE cdrom
Date
> On Tue Sep 03, 2002 at 04:49:12PM +0930, Jonathan Woithe wrote:
> > Hi all
> >
> > Yesterday I reported a problem to lkml I observed with `dd' and ide cds:
> > > For a number of years now I have duplicated cds using
> > > dd if=/dev/cdrom of=foo.iso
> > > cdrecord ... foo.iso
> > > :
> > > Today I tried the same trick under 2.4.18 and struck a problem: the kernel
> > > would not read the complete CD image. ...
> >
> > After further testing, it seems that turning off dma using "hdparm -d 0
> > /dev/hdc" allows things to work as expected - the full disk can be read and
> > the resulting image is intact. It appears therefore that the problem may
>
> Interesting. When DMA is enabled does running
> blockdev --setra 0 /dev/cdrom
> make any difference?

None at all that I can tell:
baxter:~> hdparm -d 0 /dev/hdc
/dev/hdc:
setting using_dma to 0 (off)
using_dma = 0 (off)
baxter:~> dd if=/dev/hdc of=/dev/null bs=2k skip=64008 count=8
8+0 records in
8+0 records out
baxter:~> hdparm -d 1 /dev/hdc
/dev/hdc:
setting using_dma to 1 (on)
using_dma = 1 (on)
baxter:~> dd if=/dev/hdc of=/dev/null bs=2k skip=64008 count=8
dd: reading /dev/hdc': Input/output error
4+0 records in
4+0 records out
baxter:~> blockdev --setra 0 /dev/hdc
baxter:~> dd if=/dev/hdc of=/dev/null bs=2k skip=64008 count=8
dd: reading /dev/hdc': Input/output error
4+0 records in
4+0 records out

The CD concerned definitely has 64016 data blocks as reported by isosize:
baxter:~> isosize -x /dev/hdc
sector count: 64016, sector size: 2048

When the read succeeds, the messages log gives
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256068

This is expected - 256068 is beyond the last data sector and would be one of
those unreadable runout sectors that CDs have.

When the command fails with DMA turned on, we get:
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256048
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256052
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256056
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256060
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256064
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256068

Again, it can't read 512 byte) sector 256068, but appears to fail the four
2048 byte CDROM sectors leading up to the first leadout sector as well.

Interestingly enough, if I seek 64012 blocks in and read 4 blocks, things
work:
baxter:~> dd if=/dev/hdc of=/dev/null bs=2k skip=64012 count=4
4+0 records in
4+0 records out
with
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256064
hdc: command error: status=0x51 { DriveReady SeekComplete Error }
hdc: command error: error=0x50
end_request: I/O error, dev 16:00 (hdc), sector 256068
appearing in the logs.

This is the only way to read those last 4 2k blocks: reading them from any
other skip offset (or as part of a complete disc read) results in them being
flagged with an I/O error.

Regards
jonathan
--
* Jonathan Woithe jwoithe@physics.adelaide.edu.au *
* http://www.physics.adelaide.edu.au/~jwoithe *
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