Re: sysfs support for sg

[Douglas Gilbert <dougg@torque.net>]

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Olaf Hering wrote:
>  On Wed, Jan 07, Olaf Hering wrote:
> 
> 
>>Hello,
>>
>>are there any plans to add sysfs support to the sg driver?
>>I see no 'dev' nodes for it.
>>Can stuff like 'sg_start /dev/sg2 0' be done in another way?
> 
> 
> I missed the /sys/block/sda/device/generic symlink. But still, no dev
> node. Is that supposed to work that way?

Olaf,
lk 2.6.0-rc1 has added sysfs support for sg with
/sys/cdev/major/sg<n> . In that directory
is a symlink to the corresponding SCSI device. When that symlink
is followed the target directory has a symlink called 'generic'
back to /sys/cdev/major/sg<n>. The st driver has similar cdev
bidirectional mapping (and hopefully osst will soon follow).

An example is attached. [BTW 'getcwd' returns the "true" path
as described in "man 3 getcwd".]

The "cdev" changes in the sg and st drivers allow more than
256 devices to be handled. The sg driver limits the number
of devices to 8192. I believe sd is still limited to
128 devices and I not sure about the device limits of sr.

Currently the sg driver lacks driver parameter support within sysfs
(e.g. 'allow_dio' as found in the /proc/scsi/sg directory).
Interestingly the st and osst drivers have /sys/bus/scsi/drivers/st
and osst directories (sd and st drivers also get directories if
their drivers are loaded). It is useful to be able to access
ULDs _prior_ to any (scsi) devices being attached which is not
possible under lk 2.4 .

I have been looking at the lsscsi program again which has been
dormant for 6 months. A symlink that I miss is from a scsi host
(enumerated in the /sys/class/scsi_host directory) to the
driver (and its name) that controls it.


BTW Is there a definitive libsysfs site anywhere? I noticed that
scsi_id provided in the "extras" directory of udev-009 doesn't
build with the libsysfs provided by udev-009.

Doug Gilbert




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# cd /sys/cdev/major/sg0
# ls
device
# tree
.
`-- device -> ../../../devices/pci0000:00/0000:00:0e.0/host0/0:0:1:0

1 directory, 0 files
# cd device/
# ls
block   detach_state    generic  online  queue_depth  rev         type
delete  device_blocked  model    power   rescan       scsi_level  vendor
# cd generic/
# getcwd
/sys/cdev/major/sg0