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Why does nautilus-cd-burner use sg0 instead of sr0?
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VinzC
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PostPosted: Mon Oct 31, 2005 10:45 pm    Post subject: Why does nautilus-cd-burner use sg0 instead of sr0? Reply with quote

Hi.

Sorry for the obscure title - I wanted to be as clear as possible without being truncated :) .

Something I've wondered for long: when I try to burn a CD under Gnome with Nautilus I always had to allow write access on /dev/sg0 although the CD writer is attached to /dev/sr0. What is really wierd is that the (SATA) hard disk is attached to /dev/sg0 and the CD writer is attached to /dev/sg1:
Code:
$ dmesg | grep -i scsi
SCSI subsystem initialized
scsi0 : ata_piix
  Type:   Direct-Access                      ANSI SCSI revision: 05
scsi1 : ata_piix
  Type:   CD-ROM                             ANSI SCSI revision: 05
SCSI device sda: 117210240 512-byte hdwr sectors (60012 MB)
SCSI device sda: drive cache: write back
SCSI device sda: 117210240 512-byte hdwr sectors (60012 MB)
SCSI device sda: drive cache: write back
Attached scsi disk sda at scsi0, channel 0, id 0, lun 0
sr0: scsi3-mmc drive: 24x/24x writer cd/rw xa/form2 cdda tray
Attached scsi CD-ROM sr0 at scsi1, channel 0, id 0, lun 0
Attached scsi generic sg0 at scsi0, channel 0, id 0, lun 0,  type 0
Attached scsi generic sg1 at scsi1, channel 0, id 0, lun 0,  type 5

So is there a reason why Nautilus CD burner gets confused between both SCSI busses? Is there a way to tell it to query /dev/sr0 or /dev/sg1 instead?
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seppelrockt
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PostPosted: Wed Dec 21, 2005 8:52 pm    Post subject: Reply with quote

What about the following test configuration: deleting /dev/sg0 and creating asymlink to /dev/sg1. When burning still works then cdrecord is realy confused with the scsi busses and doesn't need access to the hard disk scsi bus. If not then this access is truely needed and permissions should be handled "correctly" by udev.

Will try that later (maybe next year) cause I don't have time atm (and need a working system). All the changes should be gone after reboot anyway when udev recreates the nodes. Give it a try an let me know ;-)

EDIT: Hey cool, this is my post No. 333 - what's my price? I vote for a brand new IBM Thinkpad Z60m ;-)
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VinzC
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PostPosted: Wed Dec 21, 2005 9:54 pm    Post subject: Reply with quote

seppelrockt wrote:
What about the following test configuration: deleting /dev/sg0 and creating asymlink to /dev/sg1. When burning still works then cdrecord is realy confused with the scsi busses and doesn't need access to the hard disk scsi bus. If not then this access is truely needed and permissions should be handled "correctly" by udev.

Will try that later (maybe next year) cause I don't have time atm (and need a working system). All the changes should be gone after reboot anyway when udev recreates the nodes. Give it a try an let me know ;-)

I don't believe this will work in fact - though I'm curious giving it a try. I suspect cdrecord looks for a SCSI device capable of burning. And remember we checked SCSI CDROM support in the kernel although the CDROM device is actually IDE, connected to a SATA controller. Hence cdrecord uses sg0 instead of sg1. This is my feeling rather than an actual observation. Things might be more complicated than expected in fact. Or I haven't understood anything, which is also quite possible :-).

seppelrockt wrote:
EDIT: Hey cool, this is my post No. 333 - what's my price? I vote for a brand new IBM Thinkpad Z60m ;-)

Lol :lol: Beware of your 666'th post however ;)
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seppelrockt
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PostPosted: Wed Dec 21, 2005 11:35 pm    Post subject: Reply with quote

It appears that you are right. Indead there is no access to the scsi bus for the hd needed - the linking stuff described above works perfectly well.

So it looks like it is a cdrecord problem but I do not realy understand why it insists on using sg0 and sg1 ...

What's the next step? Changing my bug report to be against cdrecord (which is a dead project)? Hopefully the Gentoo devs can fix this!

EDIT: Even stranger it works entirely without /dev/sg0 (delete it) ...
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