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

[Mike Snitzer]

On Tue, May 29 2018 at  1:52pm -0400,
Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
> Reported-by: Arnd Bergmann <arnd@xxxxxxxx>

Thanks, I've picked this up.

Mike