SG_GET_ACCESS_COUNT ioctl problem

In the 2.4 kernel (not using devfs) the SG_GET_ACCESS_COUNT ioctl to an sg device would report the correct/expected usage count when issued to a sd disc that was mounted, accounting for the mount by the system. The 2.6 kernel does not. Is this now the expected behavior or is this a bug?

Mark,
I think you can consider that ioctl deprecated in the lk 2.6 series. The implementation of that ioctl in lk 2.6.15 is not very encouraging:

    case SG_GET_ACCESS_COUNT:
        /* faked - we don't have a real access count anymore */
        val = (sdp->device ? 1 : 0);
        return put_user(val, ip);

which will yield 1 in almost all cases. In the lk 2.6 series sysfs ** is meant to take over those sort of functions from the sg driver. However struct scsi_device (one instance per scsi device (normally a logical unit)) no longer seems to maintain an access count.

I have written about the SG_IO ioctl and its various implementations in the lk 2.6 series at:
http://www.torque.net/sg/sg_io.html

However I haven't addressed the status of the lesser used sg ioctls (e.g. SG_GET_ACCESS_COUNT) in the lk 2.6 series.

** ..._GET_ACCESS_COUNT is more of a job for procfs than
sysfs.

Quoted 21 lines

Mark,
I think you can consider that ioctl deprecated in the lk 2.6 series. The implementation of that ioctl in lk 2.6.15 is not very encouraging:

   case SG_GET_ACCESS_COUNT:
       /* faked - we don't have a real access count anymore */
       val = (sdp->device ? 1 : 0);
       return put_user(val, ip);

which will yield 1 in almost all cases. In the lk 2.6 series sysfs ** is meant to take over those sort of functions from the sg driver. However struct scsi_device (one instance per scsi device (normally a logical unit)) no longer seems to maintain an access count.

I have written about the SG_IO ioctl and its various implementations in the lk 2.6 series at:
http://www.torque.net/sg/sg_io.html

Quoted 7 lines

However I haven't addressed the status of the lesser used sg ioctls (e.g. SG_GET_ACCESS_COUNT) in the lk 2.6 series.

** ..._GET_ACCESS_COUNT is more of a job for procfs than
sysfs.

So how can one safely open an sg device that happens to be a disk? I can find no combination of open flags that will cause an open to fail if the disk happens to be mounted? You imply this ioctl is a "lesser used" ioctl? What 'was' the prefered method of doing this? It's the only method I found short of writing code to xlate the sg device into an sd device and attempting an open of that first. That's not good???

Mark,
In the lk 2.6 series you can open a disk directly (e.g. /dev/sda) and send it SCSI commands using the SG_IO ioctl. The situation is the same if you open the corresponding sg device and send SCSI commands.

What is important is which SCSI commands are sent. There is some crude filtering based on file permissions and the SCSI command opcode. Other than that, the onus is on the person sending the SCSI commands. Mounted file systems can be seen in /proc/mounts ** .

The sg driver is a pass through. The SG_GET_ACCESS_COUNT ioctl was a window to a variable which someone else removed around 18 months ago. There is little I can do other than try to explain ...