Signal when device is disconnected

Signal when device is disconnected

[Phil Endecott]

Dear Experts,

The proc/bus/usb API has an ioctl that can arrange for the application 
to receive a signal when the device is disconnected.  Is there anything 
similar for the SCSI generic (or other SCSI) APIs?

Assuming that there isn't, I think I need to either poll the device to 
see if it's still there, or listen on a netlink socket for a removal 
uevent, or I need to find the USB device corresponding to the sg device 
that I'm using and use its signal-on-removal ioctl.  In the latter 
case, is there a way to traverse from an sg device's /sys directory to 
the corresponding usb device's /sys directory?  /sys seems to be full 
of symlinks but I can't find the one that I need in this case.

Basically I have a fairly simple user-space driver for a USB SCSI 
device that uses the SCSI-generic API, and I want it to terminate 
tidily when the device is detached.

Many thanks for any advice.


Phil.

(Please Cc: me in any replies.)

Re: Signal when device is disconnected

[Douglas Gilbert]

Phil Endecott wrote:
> Dear Experts,
> 
> The proc/bus/usb API has an ioctl that can arrange for the application 
> to receive a signal when the device is disconnected.  Is there anything 
> similar for the SCSI generic (or other SCSI) APIs?
> 
> Assuming that there isn't, I think I need to either poll the device to 
> see if it's still there, or listen on a netlink socket for a removal 
> uevent, or I need to find the USB device corresponding to the sg device 
> that I'm using and use its signal-on-removal ioctl.  In the latter case, 
> is there a way to traverse from an sg device's /sys directory to the 
> corresponding usb device's /sys directory?  /sys seems to be full of 
> symlinks but I can't find the one that I need in this case.
> 
> Basically I have a fairly simple user-space driver for a USB SCSI device 
> that uses the SCSI-generic API, and I want it to terminate tidily when 
> the device is detached.

Phil,
If you are using the lk 2.6 series (from around 2.6.15) then
you could use the inotify mechanism (look at 'man inotify'
to start with). For example, you could monitor the deletion of
/sys/class/scsi_generic/sg1/dev or the corresponsing device
node: /dev/sg1 .

Doug Gilbert