block: remove BLK_DEV_DAX config option

The functionality for block device DAX was already removed with commit
acc93d30d7 ("Revert "block: enable dax for raw block devices"")

However, we still had a config option hanging around that was always
disabled because it depended on CONFIG_BROKEN.  This config option was
introduced in commit 03cdadb040 ("block: disable block device DAX by
default")

This change reverts that commit, removing the dead config option.

Link: http://lkml.kernel.org/r/20160729182314.6368-1-ross.zwisler@linux.intel.com
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

block/Kconfig

@@ -88,19 +88,6 @@ config BLK_DEV_INTEGRITY
 	T10/SCSI Data Integrity Field or the T13/ATA External Path
 	Protection.  If in doubt, say N.
 
-config BLK_DEV_DAX
-	bool "Block device DAX support"
-	depends on FS_DAX
-	depends on BROKEN
-	help
-	  When DAX support is available (CONFIG_FS_DAX) raw block
-	  devices can also support direct userspace access to the
-	  storage capacity via MMAP(2) similar to a file on a
-	  DAX-enabled filesystem.  However, the DAX I/O-path disables
-	  some standard I/O-statistics, and the MMAP(2) path has some
-	  operational differences due to bypassing the page
-	  cache.  If in doubt, say N.
-
 config BLK_DEV_THROTTLING
 	bool "Block layer bio throttling support"
 	depends on BLK_CGROUP=y

fs/block_dev.c

@@ -1275,10 +1275,6 @@ static int __blkdev_get(struct block_device *bdev, fmode_t mode, int for_part)
 		bdev->bd_disk = disk;
 		bdev->bd_queue = disk->queue;
 		bdev->bd_contains = bdev;
-		if (IS_ENABLED(CONFIG_BLK_DEV_DAX) &&
-		    blk_queue_dax(disk->queue))
-			bdev->bd_inode->i_flags = S_DAX;
-		else
 		bdev->bd_inode->i_flags = 0;
 
 		if (!partno) {