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Hi Greg,

So I've drunk the sysfs kool-aid, but I'm wrestling with the
implementation. And I apologize for a long-winded question...

I'm working on a SCSI target adapter....an adapter that lets a SCSI
initiator in another system get at local block devices as if they were
SCSI devices. The adapter device driver wants to make mappings like:

0:1 -> /dev/hda3
0:2 -> /dev/loop1

(where "0:1" is the SCSI bus/target identifier presented to the
initiator.) The mapping is currently done through the /proc file system,
and I would really like to do it via sysfs. For context, the current
implementation would do something like:
echo "b 8 16 0 1" > /proc/drivers/ibmvscsis/30000005
to create a mapping from block device 8:16 (/dev/sdb) to 0:1

Currently my adapter shows up as
./bus/vio/drivers/ibmvscss/30000005
./bus/vio/devices/30000005
./devices/vio/30000005

Each of the mappings might have a number of attributes, (the mapping
itself, whether it is active, read-only, etc.) So I think I want a
directory under the device for each mapping:

sys
|-- devices
| |
| `-- vio
| |-- 30000005
| | |-- detach_state
| | |-- name
| | |-- 0
| | | |-- 0
| | | | |-- device
| | | | |-- active
| | | | `-- read-only
| | | |-- 1
| | | | |-- device
| | | | |-- active
| | | | `-- read-only

So now to establish the mapping you would

echo "/dev/sdb3" > /sys/devices/vio/30000005/0/0/device
echo 1 > /sys/devices/vio/30000005/0/0/active

I think this follows all the nice rules for one value per attribute, but
I'm struggling with building the hierarchy in sysfs. Obviously I am going
to need a kobject for each set of attributes so that I can tell which one
is being accessed. I considered using struct devices for each level and
registering them, which seems reasonable. I also considered creating a
bus, but this seems like overkill in a single device driver.

Ultimately this has to be sane enough that Mr. Bottomley will accept it
from a SCSI point of view, and you will accept it from a sysfs point of
view.

All comments and suggestions welcomed...

Dave B
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