rd: support XIP

Support direct_access XIP method with brd.

Signed-off-by: Nick Piggin <npiggin@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 47 insertions, 2 deletions

diff --git a/drivers/block/Kconfig b/drivers/block/Kconfig
index 8be67cd3fe01..b6d230b3209f 100644
--- a/drivers/block/Kconfig
+++ b/drivers/block/Kconfig
@@ -357,6 +357,16 @@ 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
+        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
+          allocated from highmem (only a problem for highmem systems).
+
 config CDROM_PKTCDVD
         tristate "Packet writing on CD/DVD media"
         depends on !UML
diff --git a/drivers/block/brd.c b/drivers/block/brd.c
index 50b659bedc8f..85364804364f 100644
--- a/drivers/block/brd.c
+++ b/drivers/block/brd.c
@@ -89,6 +89,7 @@ static struct page *brd_insert_page(struct brd_device *brd, sector_t sector)
 {
         pgoff_t idx;
         struct page *page;
+        gfp_t gfp_flags;
 
         page = brd_lookup_page(brd, sector);
         if (page)
@@ -97,7 +98,16 @@ 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
+         * restriction might be able to be lifted.
          */
+        gfp_flags = GFP_NOIO | __GFP_ZERO;
+#ifndef CONFIG_BLK_DEV_XIP
+        gfp_flags |= __GFP_HIGHMEM;
+#endif
         page = alloc_page(GFP_NOIO | __GFP_HIGHMEM | __GFP_ZERO);
         if (!page)
                 return NULL;
@@ -307,6 +317,28 @@ out:
         return 0;
 }
 
+#ifdef CONFIG_BLK_DEV_XIP
+static int brd_direct_access (struct block_device *bdev, sector_t sector,
+                        unsigned long *data)
+{
+        struct brd_device *brd = bdev->bd_disk->private_data;
+        struct page *page;
+
+        if (!brd)
+                return -ENODEV;
+        if (sector & (PAGE_SECTORS-1))
+                return -EINVAL;
+        if (sector + PAGE_SECTORS > get_capacity(bdev->bd_disk))
+                return -ERANGE;
+        page = brd_insert_page(brd, sector);
+        if (!page)
+                return -ENOMEM;
+        *data = (unsigned long)page_address(page);
+
+        return 0;
+}
+#endif
+
 static int brd_ioctl(struct inode *inode, struct file *file,
                         unsigned int cmd, unsigned long arg)
 {
@@ -342,8 +374,11 @@ static int brd_ioctl(struct inode *inode, struct file *file,
 }
 
 static struct block_device_operations brd_fops = {
-        .owner =        THIS_MODULE,
-        .ioctl =        brd_ioctl,
+        .owner =                THIS_MODULE,
+        .ioctl =                brd_ioctl,
+#ifdef CONFIG_BLK_DEV_XIP
+        .direct_access =        brd_direct_access,
+#endif
 };
 
 /*