Re: device enumeration

On 10/5/07, Alan Stern <[email protected]> wrote:
> On Fri, 5 Oct 2007, Joe Halpin wrote:
>
> > > For example, just get the target of the /sys/block/sda/device symbolic
> > > link.  Right now on my system I have:
> > >
> > > $ ls -l /sys/block/sda/device
> > > lrwxrwxrwx 1 root root 0 Oct  5 11:13 /sys/block/sda/device ->
> > > ../../devices/pci0000:00/0000:00:1d.7/usb8/8-4/8-4:1.0/host0/target0:0:0/0:0:0:0/
> > >
> > > Depending on your hardware arrangement, one of the path components at
> > > or near the "usbN" part (usb8 above, or 8-4) should tell you which
> > > device you're looking at.
> >
> > The problem is that the internal flash gets a different address
> > depending on whether or not a usb key is plugged in. For example,
> > here's what I get when the board is booted with no key in the external
> > port:
> >
> > # ls -l /sys/block/sda/device
> > lrwxrwxrwx    1 root     0               0 Oct 23 18:31
> > /sys/block/sda/device ->
> > ../../devices/platform/ehci_platform.4523/usb1/1-1/1-1.2/1-1.2:1.0/host0/target0:0:0/0:0:0:0
>
> Okay, that's the internal flash.
>
> > This is what happens when the board is booted with a key in the external port:
> > # ls -l /sys/block/sda/device
> > lrwxrwxrwx    1 root     0               0 Oct 23 18:13
> > /sys/block/sda/device ->
> > ../../devices/platform/ehci_platform.4523/usb1/1-1/1-1.1/1-1.1:1.0/host0/target0:0:0/0:0:0:0
>
> And now that's the external key, right?  Since the flash would move to
> sdb.
>
> So now you have an easy way of telling them apart.  If you see "1-1.2"
> in the symlink path for sda, then you know sda refers to the internal
> flash.  And if you see "1-1.1" in the path, then you know sda refers to
> the external key.
>
> > So, we're looking to see if we can get udev installed. In the meantime
> > I'm checking sys for the model of the internal flash in
> > /sys/bus/scsi/drivers/sd/*/model. As you say, it's not hard, but I
> > don't like it because we have to depend on the model name of the flash
> > not changing.
>
> Using the path as described above gives the information you want, in
> terms of port numbers.  These don't depend on model names or anything
> like that, just on how the components are hooked together.

Yes, you're right. I'm trying to hard I guess. Thanks

Joe

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