map gendisk (or blockdev) -> scsi_device

map gendisk (or blockdev) -> scsi_device

[Edward Falk]

Hi all; what's the proper way to get the scsi_device structure from a 
gendisk structure?  sd.c uses pointers through scsi_disk, but that 
structure is private to sd.c.  Will I need to add an access function in 
sd.c or something?

-ed falk, efalk@google.com

RE: map gendisk (or blockdev) -> scsi_device

[Chen, Kenneth W]

Edward Falk wrote on Tuesday, July 12, 2005 5:38 PM
> Hi all; what's the proper way to get the scsi_device structure from a 
> gendisk structure?  sd.c uses pointers through scsi_disk, but that 
> structure is private to sd.c.  Will I need to add an access function in 
> sd.c or something?

If you are sure gendisk points to a scsi disk, then I think you can get
scsi_device through gendisk->queue->queuedata.

- Ken

Re: map gendisk (or blockdev) -> scsi_device

[Christoph Hellwig]

On Tue, Jul 12, 2005 at 05:38:19PM -0700, Edward Falk wrote:
> Hi all; what's the proper way to get the scsi_device structure from a 
> gendisk structure?

No.

> sd.c uses pointers through scsi_disk, but that 
> structure is private to sd.c.  Will I need to add an access function in 
> sd.c or something?

You should revisit your code to not need access to the scsi_device
structure, and follow the layering of the block and scsi subsystems.

Re: map gendisk (or blockdev) -> scsi_device

[Edward Falk]

> You should revisit your code to not need access to the scsi_device
> structure, and follow the layering of the block and scsi subsystems.

Maybe I should explain what I'm trying to do here.

Some of our software reads some of the values in /proc/ide/hda/.  We're 
porting this facility to libata-based drivers in 2.6 and moving it to 
/sysfs/block/sda/.  The sysfs show() functions will be given pointers to 
gendisk structures but will need to obtain information from the 
associated scsi_device structure.

Does anybody have any suggestions as to the "right" way to proceed?


meta:

I understand the layering of block vs scsi and so on, but I wonder why 
there's so much isolation in the kernel.  Why should it be impossible to 
obtain the gendisk structure from the scsi_device structure, or to 
obtain the block_device structure from the gendisk?

   -ed falk

Re: map gendisk (or blockdev) -> scsi_device

[Patrick Mansfield]

On Wed, Jul 13, 2005 at 11:44:34AM -0700, Edward Falk wrote:
> 
> >You should revisit your code to not need access to the scsi_device
> >structure, and follow the layering of the block and scsi subsystems.
> 
> Maybe I should explain what I'm trying to do here.
> 
> Some of our software reads some of the values in /proc/ide/hda/.  We're 
> porting this facility to libata-based drivers in 2.6 and moving it to 
> /sysfs/block/sda/.  The sysfs show() functions will be given pointers to 
> gendisk structures but will need to obtain information from the 
> associated scsi_device structure.
> 
> Does anybody have any suggestions as to the "right" way to proceed?

Add or use the attributes under the scsi_device, then use the
/sysfs/block/sd/device symlink to find the corresponding scsi_device.

This is similar to what udev and lsscsi use to find device attributes.

udev uses libsysfs (included with udev).

[elm3b79 patman]$ ls -l /sys/block/sdo/device
lrwxrwxrwx    1 root     root            0 Jul 13 16:44 /sys/block/sdo/device -> ../../devices/pci0000:01/0000:01:0c.0/host2/rport-2:0-8/target2:0:8/2:0:8:0

[elm3b79 patman]$ ls /sys/block/sdo/device/
block   device_blocked  iodone_cnt     model        rescan      state vendor
bus     driver          ioerr_cnt      queue_depth  rev         timeout
delete  iocounterbits   iorequest_cnt  queue_type   scsi_level  type

-- Patrick Mansfield

Re: map gendisk (or blockdev) -> scsi_device

[Edward Falk]

> Add or use the attributes under the scsi_device, then use the
> /sysfs/block/sd/device symlink to find the corresponding scsi_device.

Perfect!  Thanks.

Re: map gendisk (or blockdev) -> scsi_device

[Christoph Hellwig]

On Wed, Jul 13, 2005 at 04:46:54PM -0700, Patrick Mansfield wrote:
> Add or use the attributes under the scsi_device, then use the
> /sysfs/block/sd/device symlink to find the corresponding scsi_device.

yupp, the /sys/block/* attributes are really only meant to be for
thing related to the actual block device, not the underlying hardware.

Re: map gendisk (or blockdev) -> scsi_device

[Edward Falk]

Christoph Hellwig wrote:
> On Wed, Jul 13, 2005 at 04:46:54PM -0700, Patrick Mansfield wrote:
> 
>>Add or use the attributes under the scsi_device, then use the
>>/sysfs/block/sd/device symlink to find the corresponding scsi_device.
> 
> 
> yupp, the /sys/block/* attributes are really only meant to be for
> thing related to the actual block device, not the underlying hardware.

What is the difference between "actual block device" and "underlying 
hardware"?

	-ed