linux-kernel - Re: [PATCH 2/5] USB Kconfig: Select SCSI for USB Mass Storage support

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Date:	Sun, 06 Jan 2008 15:39:16 +0100
From:	Stefan Richter <stefanr@...6.in-berlin.de>
To:	Al Boldi <a1426z@...ab.com>
CC:	Sam Ravnborg <sam@...nborg.org>, Adrian Bunk <bunk@...nel.org>,
	Randy Dunlap <randy.dunlap@...cle.com>,
	linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
	David Brownell <david-b@...bell.net>, Greg KH <greg@...ah.com>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH 2/5] USB Kconfig: Select SCSI for USB Mass Storage support

Al Boldi wrote:
> Sam Ravnborg wrote:
>> And that requires you to use select only to select symbols with
>> no dependencies.
>>
>> In this case we do not know if BLOCK is enabled or not.
> 
> Good point!  How about we solve it like this:
> 
>   	menuconfig USB_STORAGE
>   	tristate "USB Mass Storage support"
> -	depends on USB && SCSI
> +	depends on USB && BLOCK
> +	select SCSI

Still wrong.  SCSI also needs HAS_DMA and SCSI_DMA.  HAS_DMA furthermore
depends on !NO_DMA.  So that would mean

menuconfig USB_STORAGE
	tristate "USB Mass Storage support"
	depends on USB && BLOCK && HAS_DMA
	select SCSI
	select SCSI_DMA

But copying all (currently existing) dependencies of SCSI to USB_STORAGE
is arguably a bad solution.  There are four other potential solutions:

  - Let kconfig look up the dependencies of SCSI.  If they are
    fulfilled, present the option USB_STORAGE and switch on SCSI if
    the user chooses USB_STORAGE.

  - Let kconfig recursively look up all dependencies of SCSI and their
    subsequent dependencies.  Try to switch them all on if the user
    chooses USB_STORAGE.  If that fails for whatever reason, say to
    the user:  I'm sorry Dave, I'm afraid I can't do that.

  - Don't use 'select' on options which have further dependencies.

  - Design and implement UIs which don't need 'select' in the first
    place.
-- 
Stefan Richter
-=====-==--- ---= --==-
http://arcgraph.de/sr/
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