brd: rename XIP to DAX

Since this is relating to FS_XIP, not KERNEL_XIP, it should be called
DAX instead of XIP.

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
Cc: Andreas Dilger <andreas.dilger@intel.com>
Cc: Boaz Harrosh <boaz@plexistor.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Theodore Ts'o <tytso@mit.edu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 14 insertions, 13 deletions

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 014a1cfc41c5..1b8094d4d7af 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -393,14 +393,15 @@ config BLK_DEV_RAM_SIZE
           The default value is 4096 kilobytes. Only change this if you know
           what you are doing.
 
-config BLK_DEV_XIP
-        bool "Support XIP filesystems on RAM block device"
-        depends on BLK_DEV_RAM
+config BLK_DEV_RAM_DAX
+        bool "Support Direct Access (DAX) to RAM block devices"
+        depends on BLK_DEV_RAM && FS_DAX
         default n
         help
-          Support XIP filesystems (such as ext2 with XIP support on) on
-          top of block ram device. This will slightly enlarge the kernel, and
-          will prevent RAM block device backing store memory from being
+          Support filesystems using DAX to access RAM block devices.  This
+          avoids double-buffering data in the page cache before copying it
+          to the block device.  Answering Y will slightly enlarge the kernel,
+          and will prevent RAM block device backing store memory from being
           allocated from highmem (only a problem for highmem systems).
 
 config CDROM_PKTCDVD
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index c01b921b1b4a..64ab4951e9d6 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -97,13 +97,13 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
          * Must use NOIO because we don't want to recurse back into the
          * block or filesystem layers from page reclaim.
          *
-         * Cannot support XIP and highmem, because our ->direct_access
-         * routine for XIP must return memory that is always addressable.
-         * If XIP was reworked to use pfns and kmap throughout, this
+         * Cannot support DAX and highmem, because our ->direct_access
+         * routine for DAX must return memory that is always addressable.
+         * If DAX was reworked to use pfns and kmap throughout, this
          * restriction might be able to be lifted.
          */
         gfp_flags = GFP_NOIO | __GFP_ZERO;
-#ifndef CONFIG_BLK_DEV_XIP
+#ifndef CONFIG_BLK_DEV_RAM_DAX
         gfp_flags |= __GFP_HIGHMEM;
 #endif
         page = alloc_page(gfp_flags);
@@ -369,7 +369,7 @@ static int brd_rw_page(struct block_device *bdev, sector_t sector,
         return err;
 }
 
-#ifdef CONFIG_BLK_DEV_XIP
+#ifdef CONFIG_BLK_DEV_RAM_DAX
 static long brd_direct_access(struct block_device *bdev, sector_t sector,
                         void **kaddr, unsigned long *pfn, long size)
 {
@@ -390,6 +390,8 @@ static long brd_direct_access(struct block_device *bdev, sector_t sector,
          */
         return PAGE_SIZE;
 }
+#else
+#define brd_direct_access NULL
 #endif
 
 static int brd_ioctl(struct block_device *bdev, fmode_t mode,
@@ -430,9 +432,7 @@ static const struct block_device_operations brd_fops = {
         .owner =                THIS_MODULE,
         .rw_page =              brd_rw_page,
         .ioctl =                brd_ioctl,
-#ifdef CONFIG_BLK_DEV_XIP
         .direct_access =        brd_direct_access,
-#endif
 };
 
 /*