From mboxrd@z Thu Jan  1 00:00:00 1970
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Date: Tue, 29 May 2018 15:57:40 -0400
From: Mike Snitzer <snitzer@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Mikulas Patocka <mpatocka@redhat.com>,
        Shaohua Li <shli@kernel.org>, Alasdair Kergon <agk@redhat.com>,
        device-mapper development <dm-devel@redhat.com>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        linux-fsdevel <linux-fsdevel@vger.kernel.org>,
        Heinz Mauelshagen <heinzm@redhat.com>,
        linux-raid <linux-raid@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: dm-writecache: fix compilation issue with !DAX
Message-ID: <20180529195740.GA386@redhat.com>
References: <20180528153834.2268557-1-arnd@arndb.de>
 <20180529175216.24937-1-ross.zwisler@linux.intel.com>
 <20180529180823.GA32763@redhat.com>
 <CAPcyv4iF8oAGDKcWP++-bw5OcfmkSTPHCAw1XZvVRTz4evJvGw@mail.gmail.com>
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On Tue, May 29 2018 at  2:40pm -0400,
Dan Williams <dan.j.williams@intel.com> wrote:

> On Tue, May 29, 2018 at 11:08 AM, Mike Snitzer <snitzer@redhat.com> wrote:
> > On Tue, May 29 2018 at  1:52pm -0400,
> > Ross Zwisler <ross.zwisler@linux.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@linux.intel.com>
> >> Reported-by: Arnd Bergmann <arnd@arndb.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?

Yeah, I'm going to pivot back to that and put time to it shortly.  If
dm-writecache has to wait another cycle (so 4.19 inclusion), while
unfortunate, it wouldn't be the end of the world.

I look forward to your continued help, thanks.
Mike