linux-kernel - Re: Possible bug in SCSI Kconfig

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Message-ID: <b637ec0b0810221248g40b02712n59e26c4f614657b@mail.gmail.com>
Date:	Wed, 22 Oct 2008 21:48:57 +0200
From:	"Fabio Comolli" <fabio.comolli@...il.com>
To:	"James Bottomley" <James.Bottomley@...senpartnership.com>
Cc:	"Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
	sam@...nborg.org, linux-scsi <linux-scsi@...r.kernel.org>
Subject: Re: Possible bug in SCSI Kconfig

Hi.

On Wed, Oct 22, 2008 at 9:44 PM, James Bottomley
<James.Bottomley@...senpartnership.com> wrote:
> On Wed, 2008-10-22 at 21:25 +0200, Fabio Comolli wrote:
>> Hi.
>>
>> On Wed, Oct 22, 2008 at 9:05 PM, James Bottomley
>> <James.Bottomley@...senpartnership.com> wrote:
>> > On Wed, 2008-10-22 at 18:29 +0200, Fabio Comolli wrote:
>> >> Hi.
>> >> In kernel 2.6.27.2 - drivers/scsi/Kconfig we have:
>> >>
>> >> config SCSI_WAIT_SCAN
>> >>         tristate
>> >>         default m
>> >>         depends on SCSI
>> >>         depends on MODULES
>> >>
>> >> The tristate field is empty. This has the effect that this option is
>> >> not visible in menuconfig and so it's always selected. The default is
>> >> "m" for all architectures and so this module is always compiled if
>> >> SCSI and MODULES are both enabled.
>> >>
>> >> I'm using a patch like this one:
>> >>
>> >>  config SCSI_WAIT_SCAN
>> >> -     tristate
>> >> +     tristate "Wait until all the async scans are complete"
>> >>       default m
>> >>       depends on SCSI
>> >>       depends on MODULES
>> >>
>> >> to get rid of that module.
>> >>
>> >> Of course, I have no idea if this is correct or the current behavior
>> >> is the expected one.
>> >
>> > The point of all of this is that if you enable async scanning, you need
>> > a method of waiting for the scans to complete, which is all this module
>> > does (you insert it and it doesn't come back from the insertion until
>> > all the pending async scans are complete).  It's tristate because really
>> > it only makes sense to be M or N.  The consensus is that, given async
>> > scanning is always an option, this function should always be built as a
>> > module *if* modules and SCSI are enabled ... because you might have a
>> > HBA module you enabled async scanning for and you need to wait.
>>
>> OK, I see your point.
>>
>> But in my case I have SCSI enabled only because it's SELECTed by ATA
>> (it's just a laptop) and I don't have any hba's and never will. So no
>> async scan.
>
> Presumably you have a laptop hard disk.  That's currently SCSI if you
> use ATA ... although when ATA moves out of SCSI it will no longer be, so
> you could regard this as a temporary condition.

Ok.

>
>> Maybe this module should be enabled if async scan is.
>
> But that's the point: async scan is always "enabled" it just might not
> be the default, that's what the CONFIG_SCSI_SCAN_ASYNC controls: the
> default value (but you can always turn it on with the kernel boot or
> SCSI module option).  Async scan is also functional for /drivers/ata and
> other hot plug type busses, so it still makes sense for them as well.
>

I see the point.

>> > There's really not much point giving the user the choice, since this
>> > module is part of the initrd sequence ... it's not really anything a
>> > user would want to use stand alone, hence there's no point giving a
>> > choice about it.
>> >
>>
>> I don't use initrd at all. I just noticed the existence of this module
>> while trying to have a non modular kernel. This failed because of
>> ipw2200 and after having enabled modules again I just found this
>> scsi_wait_scan.ko.
>
> Well, we do use CONFIG_MODULES to try to discern whether the user wants
> modules or not.  However, if you enable modules, we'd need some
> telepathic configurator to tell us if you plan to use SCSI HBA modules
> or not, so the safest course is always to enable it.  The real point is
> that you have to be a real power user to answer N correctly to this, so
> it's better not to confuse the remaining 97% with the option because
> they could easily get wrong ... the 3% who're sure they don't want it
> can simply delete it.
>

Thanks for your explanation.

> James
>

Regards,
Fabio

>
>
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