read only scsi disk

read only scsi disk

[Ming Zhang]

Hi folks

Could anybody shed a light on this?

We are adding the support for an OSS iscsi target to support export an
iscsi disk as readonly. We set correct read only bit in sense dbd. But
we found that only when we set the removable bit, the linux will
actually check the ro bit. more detail information can be found from

http://sourceforge.net/mailarchive/forum.php?thread_id=9682261&forum_id=40837

from sd.c, it looks like removable is judged first.

             if (sdp->removable)
                   sd_read_write_protect_flag(sdkp, disk->disk_name,
                                                   buffer);


so is there special reason that we should judge removable before we see
if write protect?

thanks!

Ming

Re: read only scsi disk

[Matthew Wilcox]

On Thu, Feb 09, 2006 at 12:04:07PM -0500, Ming Zhang wrote:
> We are adding the support for an OSS iscsi target to support export an
> iscsi disk as readonly. We set correct read only bit in sense dbd. But
> we found that only when we set the removable bit, the linux will
> actually check the ro bit. more detail information can be found from

Surely all iSCSI discs are removable, since anyone could unplug the
network cable at any time ...

Re: read only scsi disk

[Ming Zhang]

so fc disk is also removable, since anyone could unplug the fc cable at
any time...

so even parallel scsi disk, sata disk...

i donot think this is a good reason. ;)

ming

On Thu, 2006-02-09 at 12:02 -0700, Matthew Wilcox wrote:
> On Thu, Feb 09, 2006 at 12:04:07PM -0500, Ming Zhang wrote:
> > We are adding the support for an OSS iscsi target to support export an
> > iscsi disk as readonly. We set correct read only bit in sense dbd. But
> > we found that only when we set the removable bit, the linux will
> > actually check the ro bit. more detail information can be found from
> 
> Surely all iSCSI discs are removable, since anyone could unplug the
> network cable at any time ...

RE: read only scsi disk

[berthiaume_wayne]

I seem to recall this behavior had something to do with the handling of
CD/ROM disks at one time.

Regards,
Wayne. 

-----Original Message-----
From: linux-scsi-owner@vger.kernel.org
[mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of Ming Zhang
Sent: Thursday, February 09, 2006 2:19 PM
To: Matthew Wilcox
Cc: linux-scsi; Damian Pietras
Subject: Re: read only scsi disk

so fc disk is also removable, since anyone could unplug the fc cable at
any time...

so even parallel scsi disk, sata disk...

i donot think this is a good reason. ;)

ming

On Thu, 2006-02-09 at 12:02 -0700, Matthew Wilcox wrote:
> On Thu, Feb 09, 2006 at 12:04:07PM -0500, Ming Zhang wrote:
> > We are adding the support for an OSS iscsi target to support export an
> > iscsi disk as readonly. We set correct read only bit in sense dbd. But
> > we found that only when we set the removable bit, the linux will
> > actually check the ro bit. more detail information can be found from
> 
> Surely all iSCSI discs are removable, since anyone could unplug the
> network cable at any time ...

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Re: read only scsi disk

[Stefan Richter]

Ming Zhang wrote:
> from sd.c, it looks like removable is judged first.
> 
>              if (sdp->removable)
>                    sd_read_write_protect_flag(sdkp, disk->disk_name,
>                                                    buffer);

This has been changed in the meantime. Check the current sources.
-- 
Stefan Richter
-=====-=-==- --=- -=--=
http://arcgraph.de/sr/

RE: read only scsi disk

[Ming Zhang]

thx.

but if i am correct, cdrom is handled in sr while disk is handled in sd.
so they are independent issues. of course, might be same reason. :P

the key here is why sd.c need to judge write protect only for removable
disk. is there no case that a disk is read only but not removable? for
example, if later a secure disk has internal security protection and
after authentication, the allowed option is only to read? this can be
common for networked disks.

ming




On Thu, 2006-02-09 at 14:32 -0500, berthiaume_wayne@emc.com wrote:
> I seem to recall this behavior had something to do with the handling of
> CD/ROM disks at one time.
> 
> Regards,
> Wayne. 
> 
> -----Original Message-----
> From: linux-scsi-owner@vger.kernel.org
> [mailto:linux-scsi-owner@vger.kernel.org] On Behalf Of Ming Zhang
> Sent: Thursday, February 09, 2006 2:19 PM
> To: Matthew Wilcox
> Cc: linux-scsi; Damian Pietras
> Subject: Re: read only scsi disk
> 
> so fc disk is also removable, since anyone could unplug the fc cable at
> any time...
> 
> so even parallel scsi disk, sata disk...
> 
> i donot think this is a good reason. ;)
> 
> ming
> 
> On Thu, 2006-02-09 at 12:02 -0700, Matthew Wilcox wrote:
> > On Thu, Feb 09, 2006 at 12:04:07PM -0500, Ming Zhang wrote:
> > > We are adding the support for an OSS iscsi target to support export an
> > > iscsi disk as readonly. We set correct read only bit in sense dbd. But
> > > we found that only when we set the removable bit, the linux will
> > > actually check the ro bit. more detail information can be found from
> > 
> > Surely all iSCSI discs are removable, since anyone could unplug the
> > network cable at any time ...
> 
> -
> To unsubscribe from this list: send the line "unsubscribe linux-scsi" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

Re: read only scsi disk

[Ming Zhang]

thx, i found this was changed in at least 2.6.16-rc2.

ming



On Thu, 2006-02-09 at 20:36 +0100, Stefan Richter wrote:
> Ming Zhang wrote:
> > from sd.c, it looks like removable is judged first.
> > 
> >              if (sdp->removable)
> >                    sd_read_write_protect_flag(sdkp, disk->disk_name,
> >                                                    buffer);
> 
> This has been changed in the meantime. Check the current sources.

Re: read only scsi disk

[Stefan Richter]

Matthew Wilcox wrote:
> Surely all iSCSI discs are removable, since anyone could unplug the
> network cable at any time ...

AFAIU, sdev->removable is about the medium, not about the device. Media 
can be hot-removed, devices can be hot-unplugged. (Of course an iSCSI 
target could implement removable media too.)
-- 
Stefan Richter
-=====-=-==- --=- -=--=
http://arcgraph.de/sr/

Re: read only scsi disk

[Ming Zhang]

yes, this is more accurate. thx.

ming


On Thu, 2006-02-09 at 20:54 +0100, Stefan Richter wrote:
> Matthew Wilcox wrote:
> > Surely all iSCSI discs are removable, since anyone could unplug the
> > network cable at any time ...
> 
> AFAIU, sdev->removable is about the medium, not about the device. Media 
> can be hot-removed, devices can be hot-unplugged. (Of course an iSCSI 
> target could implement removable media too.)

Re: read only scsi disk

[Stefan Richter]

Ming Zhang wrote:
> thx, i found this was changed in at least 2.6.16-rc2.

> On Thu, 2006-02-09 at 20:36 +0100, Stefan Richter wrote:
>>Ming Zhang wrote:
>>>from sd.c, it looks like removable is judged first.
>>>
>>>             if (sdp->removable)
>>>                   sd_read_write_protect_flag(sdkp, disk->disk_name,
>>>                                                   buffer);
>>
>>This has been changed in the meantime. Check the current sources.

PS: It was discussed and changed in December.
http://marc.theaimsgroup.com/?t=113406630600001
http://marc.theaimsgroup.com/?l=linux-scsi&m=113414617020021
http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=38d76df2f5483478dee803cb6e39da5e506a6643
(Note: Commit date refers to James' tree. It went into Linus' tree later 
after release of 2.6.15 but before 2.6.16-rc1.)
-- 
Stefan Richter
-=====-=-==- --=- -=--=
http://arcgraph.de/sr/

Re: read only scsi disk

[Ming Zhang]

thanks!

ming

On Thu, 2006-02-09 at 21:57 +0100, Stefan Richter wrote:
> Ming Zhang wrote:
> > thx, i found this was changed in at least 2.6.16-rc2.
> 
> > On Thu, 2006-02-09 at 20:36 +0100, Stefan Richter wrote:
> >>Ming Zhang wrote:
> >>>from sd.c, it looks like removable is judged first.
> >>>
> >>>             if (sdp->removable)
> >>>                   sd_read_write_protect_flag(sdkp, disk->disk_name,
> >>>                                                   buffer);
> >>
> >>This has been changed in the meantime. Check the current sources.
> 
> PS: It was discussed and changed in December.
> http://marc.theaimsgroup.com/?t=113406630600001
> http://marc.theaimsgroup.com/?l=linux-scsi&m=113414617020021
> http://www.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=38d76df2f5483478dee803cb6e39da5e506a6643
> (Note: Commit date refers to James' tree. It went into Linus' tree later 
> after release of 2.6.15 but before 2.6.16-rc1.)

Re: read only scsi disk

[Christoph Hellwig]

On Thu, Feb 09, 2006 at 12:02:25PM -0700, Matthew Wilcox wrote:
> On Thu, Feb 09, 2006 at 12:04:07PM -0500, Ming Zhang wrote:
> > We are adding the support for an OSS iscsi target to support export an
> > iscsi disk as readonly. We set correct read only bit in sense dbd. But
> > we found that only when we set the removable bit, the linux will
> > actually check the ro bit. more detail information can be found from
> 
> Surely all iSCSI discs are removable, since anyone could unplug the
> network cable at any time ...

The removable flags means a removeable medium.  All devices are treated as
beeing able to just go away when the transport is disconnected or the HBA
removed.