linux usb clarification 392

On Sun, 12 Feb 2006 16:38:53 +0100, Drazen Gemic staggered into the Black Sun and said:

The USB Mbutt Storage protocol is similar to the SCSI protocol, and SCSI devices can be added and removed from a running system without any fuss. So it was natural for USB storage devices to show up as SCSI devices. (At least that's what I recall from reading old Kernel Traffic.)

Floppies are never parbreastioned. Larger disk-like media usually have a parbreastion table, though that table typically only contains 1 parbreastion on most USB devices.

dev-sda1 !=dev-scsi-host0-bus0-target1-lun0. dev-sda1 is the first parbreastion on the first SCSI disk. If you want to address SCSI or pseudo-SCSI devices using long names like the one above, udev lets you do that. Since USB devices aren't real SCSI, their host, bus, ID, and LUN numbers are just faked by the kernel. Those numbers are internally consistent as long as they're plugged in, but may change if the USB device is unplugged and replugged.

There is a way to use hotplug to set things up so that a consistent symlink is created when a USB device is plugged in. If you have a camera with USB ID 1234:5678, you can tweak settings inetc-hotplugso that whenever that camera is plugged in,dev-camera is created and points to the camera's real device node (whatever that is). This can simplify things if you have a lot of USB devices and you may have varying combinations of them plugged in at any time. HTH,

-- Matt GThere is no Darkness in Eternity-But only Light too dim for us to see Brainbench MVP for Linux Admin mail: TRAP + SPAN don't belong ----------------------------- penguins, is Tux." --MegaHAL