block: remove BLK_DEV_DAX config option

The functionality for block device DAX was already removed with commit
acc93d3 ("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 03cdadb ("block: disable block device DAX by
default")

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

Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Ross Zwisler <[email protected]>
Cc: Dave Hansen <[email protected]>
Acked-by: Dan Williams <[email protected]>
Cc: Jens Axboe <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

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

@@ -1275,11 +1275,7 @@ 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;
+		bdev->bd_inode->i_flags = 0;
 
 		if (!partno) {
 			ret = -ENXIO;