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From: Dan Williams <dan.j.williams@intel.com>
Date: Mon, 28 May 2018 11:18:58 -0700
Message-ID: <CAPcyv4gpMhBaUdy=UY9M0-2QomycGZCo+K6o+Dzjdc4jmPjrkg@mail.gmail.com>
Subject: Re: [PATCH] dm: writecache: add DAX dependency
To: Arnd Bergmann <arnd@arndb.de>
Cc: Mikulas Patocka <mpatocka@redhat.com>,
        Shaohua Li <shli@kernel.org>, Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@redhat.com>,
        device-mapper development <dm-devel@redhat.com>,
        Matthew Wilcox <mawilcox@microsoft.com>,
        Ross Zwisler <ross.zwisler@linux.intel.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>
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On Mon, May 28, 2018 at 8:38 AM, Arnd Bergmann <arnd@arndb.de> wrote:
> The new dm-writecache driver inconditionally uses the dax
> subsystem, leading to link errors in some configurations:
>
> 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'
>
> It seems wrong to require DAX in order to build the writecache
> driver, but that at least avoids randconfig build errors.
>
> Fixes: bb15b431d650 ("dm: add writecache target")
> Signed-off-by: Arnd Bergmann <arnd@arndb.de>
> ---
>  drivers/md/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/md/Kconfig b/drivers/md/Kconfig
> index 852c7ebe2902..f8ecf2da1edf 100644
> --- a/drivers/md/Kconfig
> +++ b/drivers/md/Kconfig
> @@ -338,6 +338,7 @@ config DM_CACHE_SMQ
>  config DM_WRITECACHE
>         tristate "Writecache target"
>         depends on BLK_DEV_DM
> +       depends on DAX

This should probably be depends on DAX && DAX_DRIVER as we at least
need pmem or dcssblk enabled to provide a dax capable block device for
DM to claim.