Re: Question on the removable flag of USB devices

From: Matthew Dharm
Date: Tue May 26 2009 - 13:34:57 EST

On Tue, May 26, 2009 at 06:36:09PM +0200, Stefan Richter wrote:
> Matthew Dharm wrote:
> > On Mon, May 25, 2009 at 01:45:54PM -0300, Rogério Brito wrote:
> >> The question is: how are devices determined to be removable or not?
> >> Sorry if this question is too naive.
> >
> > It's a bit that the device reports. The usb-storage driver passes this bit
> > to the SCSI layer.
> Wasn't this bit actually about removable _media_ rather than
> hotpluggable transports? (I.e. hardware where you can pull the medium
> out of the drive mechanism.) So in this sense, an USB attached HDD
> should actually not present itself as "removable" unless it's a SyQuest
> or Zip or something like that.

In fact, yes, that's the meaning of that bit. The device indicates if the
storage media may be removed from the device.

That said, a great many devices simply lie about this. Probably developers
doing a cut-and-paste from templates which have the bit set one way or the
other. The "popular" OSes don't seem to really care much about this bit...


Matthew Dharm Home: mdharm-usb@xxxxxxxxxxxxxxxxxx
Maintainer, Linux USB Mass Storage Driver

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