Hi Darrick,

I love your patch! Yet something to improve:

[auto build test ERROR on linus/master]
[also build test ERROR on v4.17-rc6]
[cannot apply to dm/for-next]
[if your patch is applied to the wrong git tree, please drop us a note to help improve the system]

url:    https://github.com/0day-ci/linux/commits/Ross-Zwisler/Fix-DM-DAX-handling/20180526-212746
config: i386-randconfig-x014-201820 (attached as .config)
compiler: gcc-7 (Debian 7.3.0-16) 7.3.0
reproduce:
        # save the attached .config to linux build tree
        make ARCH=i386 

All errors (new ones prefixed by >>):

>> drivers//dax/super.c:85:5: error: redefinition of 'bdev_dax_supported'
    int bdev_dax_supported(struct block_device *bdev, int blocksize)
        ^~~~~~~~~~~~~~~~~~
   In file included from drivers//dax/super.c:23:0:
   include/linux/dax.h:82:19: note: previous definition of 'bdev_dax_supported' was here
    static inline int bdev_dax_supported(struct block_device *bdev,
                      ^~~~~~~~~~~~~~~~~~

vim +/bdev_dax_supported +85 drivers//dax/super.c

    74	
    75	/**
    76	 * bdev_dax_supported() - Check if the device supports dax for filesystem
    77	 * @bdev: block device to check
    78	 * @blocksize: The block size of the device
    79	 *
    80	 * This is a library function for filesystems to check if the block device
    81	 * can be mounted with dax option.
    82	 *
    83	 * Return: negative errno if unsupported, 0 if supported.
    84	 */
  > 85	int bdev_dax_supported(struct block_device *bdev, int blocksize)
    86	{
    87		struct dax_device *dax_dev;
    88		pgoff_t pgoff;
    89		int err, id;
    90		void *kaddr;
    91		pfn_t pfn;
    92		long len;
    93		char buf[BDEVNAME_SIZE];
    94	
    95		if (blocksize != PAGE_SIZE) {
    96			pr_debug("%s: error: unsupported blocksize for dax\n",
    97					bdevname(bdev, buf));
    98			return -EINVAL;
    99		}
   100	
   101		err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
   102		if (err) {
   103			pr_debug("%s: error: unaligned partition for dax\n",
   104					bdevname(bdev, buf));
   105			return err;
   106		}
   107	
   108		dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
   109		if (!dax_dev) {
   110			pr_debug("%s: error: device does not support dax\n",
   111					bdevname(bdev, buf));
   112			return -EOPNOTSUPP;
   113		}
   114	
   115		id = dax_read_lock();
   116		len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
   117		dax_read_unlock(id);
   118	
   119		put_dax(dax_dev);
   120	
   121		if (len < 1) {
   122			pr_debug("%s: error: dax access failed (%ld)\n",
   123					bdevname(bdev, buf), len);
   124			return len < 0 ? len : -EIO;
   125		}
   126	
   127		if (IS_ENABLED(CONFIG_FS_DAX_LIMITED) && pfn_t_special(pfn)) {
   128			/*
   129			 * An arch that has enabled the pmem api should also
   130			 * have its drivers support pfn_t_devmap()
   131			 *
   132			 * This is a developer warning and should not trigger in
   133			 * production. dax_flush() will crash since it depends
   134			 * on being able to do (page_address(pfn_to_page())).
   135			 */
   136			WARN_ON(IS_ENABLED(CONFIG_ARCH_HAS_PMEM_API));
   137		} else if (pfn_t_devmap(pfn)) {
   138			/* pass */;
   139		} else {
   140			pr_debug("%s: error: dax support not enabled\n",
   141					bdevname(bdev, buf));
   142			return -EOPNOTSUPP;
   143		}
   144	
   145		return 0;
   146	}
   147	EXPORT_SYMBOL_GPL(bdev_dax_supported);
   148	#endif
   149	

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