Re: [linux-usb-devel] Re: hotplugging to deal with firmware download

[David Brownell <david-b@pacbell.net>]

Andries.Brouwer@cwi.nl wrote:
>>I seem to recall pointing you at usb-storage once already,
>>as the only USB driver today which needs to do such stuff.
>>It has a notion of device identity, based ISTR on serial
>>numbers, and saves that state. UTSL.
> 
> 
> You quote this as an example of how to do things.
> I am not especially happy with the results.

My point was only that when asked for an example,
I had already provided one ... :)

You're saying you don't like the model adopted by
usb-storage, which is your prerogative.  The person
to talk to about that is Matt Dharm.


> My experience: take a handful of compact flash card readers,
> plug them randomly into some hubs, take a handful of compact
> flash cards, plug them randomly into some readers. Now remove
> and repeat. I find it impossible to predict which device will
> get which name. Sometimes the name goes with the card, sometimes
> with the reader, sometimes neither of the two, sometimes both(!).

That does seem troublesome.  It should be one or the other,
consistently.  And "both" seems buglike.


> (Yes, it happens that I access the same card both via sdc and sde.)
> Probably things would become clear if I would read the code,
> but I haven't done so yet.
> 
> Andries
> 
> 
> [Names that go with the card are really confusing. It is as if
> one has A:/B:, that is fd0/fd1, and the name of the floppy reader
> depends on the floppy inserted, so that one has to remember the
> history. Bad.]

Named media is one of the standard models for volume management,
and I'm used to seeing that be done without regard to low-level
device naming.  For USB, there's an additional issue of being able
to assign names to the devices ... like (external) "fd0" is "fd0"
no matter which connector it's plugged in to, if it's got a serial
number providing some notion of identity.

- Dave




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