linux-kernel - Re: dm-writecache: fix compilation issue with !DAX

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Message-ID: <CAPcyv4iF8oAGDKcWP++-bw5OcfmkSTPHCAw1XZvVRTz4evJvGw@mail.gmail.com>
Date:   Tue, 29 May 2018 11:40:50 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Mike Snitzer <snitzer@...hat.com>
Cc:     Ross Zwisler <ross.zwisler@...ux.intel.com>,
        Arnd Bergmann <arnd@...db.de>,
        Mikulas Patocka <mpatocka@...hat.com>,
        Shaohua Li <shli@...nel.org>, Alasdair Kergon <agk@...hat.com>,
        device-mapper development <dm-devel@...hat.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Heinz Mauelshagen <heinzm@...hat.com>,
        linux-raid <linux-raid@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: dm-writecache: fix compilation issue with !DAX

On Tue, May 29, 2018 at 11:08 AM, Mike Snitzer <snitzer@...hat.com> wrote:
> On Tue, May 29 2018 at  1:52pm -0400,
> Ross Zwisler <ross.zwisler@...ux.intel.com> wrote:
>
>> As reported by Arnd (https://lkml.org/lkml/2018/5/28/1697), dm-writecache
>> will fail with link errors in configs where DAX isn't present:
>>
>> drivers/md/dm-writecache.o: In function `writecache_ctr':
>> dm-writecache.c:(.text+0x1fdc): undefined reference to `dax_read_lock'
>> dm-writecache.c:(.text+0x2004): undefined reference to `dax_direct_access'
>> dm-writecache.c:(.text+0x21cc): undefined reference to `dax_read_unlock'
>>
>> Fix this by following the lead of the other DM modules and wrapping calls
>> to the generic DAX code in #if IS_ENABLED(CONFIG_DAX_DRIVER) blocks.
>>
>> We also expand the failure case for the 'p' (persistent memory) flag so
>> that fails on both architectures that don't support persistent memory and
>> on kernels that don't have DAX support configured.  This prevents us from
>> ever hitting the BUG() in the persistent_memory_claim() stub.
>>
>> Signed-off-by: Ross Zwisler <ross.zwisler@...ux.intel.com>
>> Reported-by: Arnd Bergmann <arnd@...db.de>
>
> Thanks, I've picked this up.

...I assume you're also going to let the 'pmem api' discussion resolve
before this all goes upstream?