linux-kernel - Re: [PATCH, RESEND] scsi: lpfc: fix linking against modular NVMe support

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Message-ID: <CAK8P3a2EnPuTNU0O5va+Xz3nCthhpz3Po1z7SOVRiAUV_2+OhA@mail.gmail.com>
Date:   Wed, 26 Jul 2017 11:16:10 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Johannes Thumshirn <jthumshirn@...e.de>
Cc:     "James E.J. Bottomley" <jejb@...ux.vnet.ibm.com>,
        "Martin K. Petersen" <martin.petersen@...cle.com>,
        "# 3.4.x" <stable@...r.kernel.org>, Hannes Reinecke <hare@...e.de>,
        Finn Thain <fthain@...egraphics.com.au>,
        James Smart <jsmart2021@...il.com>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH, RESEND] scsi: lpfc: fix linking against modular NVMe support

On Wed, Jul 26, 2017 at 11:08 AM, Johannes Thumshirn <jthumshirn@...e.de> wrote:
> On Fri, Jul 21, 2017 at 10:53:46PM +0200, Arnd Bergmann wrote:
>> I originally sent the patch in March 2013, the day after the broken
>                                        ^ 2017?

Oops. Let me resend that.

>> +     depends on NVME_TARGET_FC || NVME_TARGET_FC=n
>> +     depends on NVME_FC || NVME_FC=n
>
> OK Kconfig is black magic, but X || X=n ? I have no doubt you do the right
> thing, I just don't understand it.

We use this construct in many places these days. A few years ago I added
a comment whenever I added an instance, but most others don't so I treat
it as an idiom now.

"depends on X" means that if X=m, the current symbol can only be "m" or
"n", while "X=y" means it can have any value.

So for "depends on X || X=n", the current symbol cannot be "y" when "X=m",
but otherwise can have any of the three possibilities. This is exactly what
we need here.

       Arnd