block, dax: move "select DAX" from BLOCK to FS_DAX

For configurations that do not enable DAX filesystems or drivers, do not
require the DAX core to be built.

Given that the 'direct_access' method has been removed from
'block_device_operations', we can also go ahead and remove the
block-related dax helper functions from fs/block_dev.c to
drivers/dax/super.c. This keeps dax details out of the block layer and
lets the DAX core be built as a module in the FS_DAX=n case.

Filesystems need to include dax.h to call bdev_dax_supported().

Cc: linux-xfs@vger.kernel.org
Cc: Jens Axboe <axboe@kernel.dk>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Jan Kara <jack@suse.com>
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

9 files changed, 102 insertions, 71 deletions

diff --git a/block/Kconfig b/block/Kconfig
index 93da7fc3f254..e9f780f815f5 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -6,7 +6,6 @@ menuconfig BLOCK
        default y
        select SBITMAP
        select SRCU
-       select DAX
        help
          Provide block layer support for the kernel.
 
diff --git a/drivers/dax/super.c b/drivers/dax/super.c
index 465dcd7317d5..e8998d15f3cd 100644
--- a/drivers/dax/super.c
+++ b/drivers/dax/super.c
@@ -14,6 +14,7 @@
 #include <linux/module.h>
 #include <linux/mount.h>
 #include <linux/magic.h>
+#include <linux/genhd.h>
 #include <linux/cdev.h>
 #include <linux/hash.h>
 #include <linux/slab.h>
@@ -47,6 +48,75 @@ void dax_read_unlock(int id)
 }
 EXPORT_SYMBOL_GPL(dax_read_unlock);
 
+int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
+                pgoff_t *pgoff)
+{
+        phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;
+
+        if (pgoff)
+                *pgoff = PHYS_PFN(phys_off);
+        if (phys_off % PAGE_SIZE || size % PAGE_SIZE)
+                return -EINVAL;
+        return 0;
+}
+EXPORT_SYMBOL(bdev_dax_pgoff);
+
+/**
+ * __bdev_dax_supported() - Check if the device supports dax for filesystem
+ * @sb: The superblock of the device
+ * @blocksize: The block size of the device
+ *
+ * This is a library function for filesystems to check if the block device
+ * can be mounted with dax option.
+ *
+ * Return: negative errno if unsupported, 0 if supported.
+ */
+int __bdev_dax_supported(struct super_block *sb, int blocksize)
+{
+        struct block_device *bdev = sb->s_bdev;
+        struct dax_device *dax_dev;
+        pgoff_t pgoff;
+        int err, id;
+        void *kaddr;
+        pfn_t pfn;
+        long len;
+
+        if (blocksize != PAGE_SIZE) {
+                pr_err("VFS (%s): error: unsupported blocksize for dax\n",
+                                sb->s_id);
+                return -EINVAL;
+        }
+
+        err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
+        if (err) {
+                pr_err("VFS (%s): error: unaligned partition for dax\n",
+                                sb->s_id);
+                return err;
+        }
+
+        dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
+        if (!dax_dev) {
+                pr_err("VFS (%s): error: device does not support dax\n",
+                                sb->s_id);
+                return -EOPNOTSUPP;
+        }
+
+        id = dax_read_lock();
+        len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
+        dax_read_unlock(id);
+
+        put_dax(dax_dev);
+
+        if (len < 1) {
+                pr_err("VFS (%s): error: dax access failed (%ld)",
+                                sb->s_id, len);
+                return len < 0 ? len : -EIO;
+        }
+
+        return 0;
+}
+EXPORT_SYMBOL_GPL(__bdev_dax_supported);
+
 /**
  * struct dax_device - anchor object for dax services
  * @inode: core vfs
diff --git a/fs/Kconfig b/fs/Kconfig
index 83eab52fb3f6..b0e42b6a96b9 100644
--- a/fs/Kconfig
+++ b/fs/Kconfig
@@ -39,6 +39,7 @@ config FS_DAX
         depends on MMU
         depends on !(ARM || MIPS || SPARC)
         select FS_IOMAP
+        select DAX
         help
           Direct Access (DAX) can be used on memory-backed block devices.
           If the block device supports DAX and the filesystem supports DAX,
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 666367e13711..3096ecd48304 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -718,72 +718,6 @@ int bdev_write_page(struct block_device *bdev, sector_t sector,
 }
 EXPORT_SYMBOL_GPL(bdev_write_page);
 
-int bdev_dax_pgoff(struct block_device *bdev, sector_t sector, size_t size,
-                pgoff_t *pgoff)
-{
-        phys_addr_t phys_off = (get_start_sect(bdev) + sector) * 512;
-
-        if (pgoff)
-                *pgoff = PHYS_PFN(phys_off);
-        if (phys_off % PAGE_SIZE || size % PAGE_SIZE)
-                return -EINVAL;
-        return 0;
-}
-EXPORT_SYMBOL(bdev_dax_pgoff);
-
-/**
- * bdev_dax_supported() - Check if the device supports dax for filesystem
- * @sb: The superblock of the device
- * @blocksize: The block size of the device
- *
- * This is a library function for filesystems to check if the block device
- * can be mounted with dax option.
- *
- * Return: negative errno if unsupported, 0 if supported.
- */
-int bdev_dax_supported(struct super_block *sb, int blocksize)
-{
-        struct block_device *bdev = sb->s_bdev;
-        struct dax_device *dax_dev;
-        pgoff_t pgoff;
-        int err, id;
-        void *kaddr;
-        pfn_t pfn;
-        long len;
-
-        if (blocksize != PAGE_SIZE) {
-                vfs_msg(sb, KERN_ERR, "error: unsupported blocksize for dax");
-                return -EINVAL;
-        }
-
-        err = bdev_dax_pgoff(bdev, 0, PAGE_SIZE, &pgoff);
-        if (err) {
-                vfs_msg(sb, KERN_ERR, "error: unaligned partition for dax");
-                return err;
-        }
-
-        dax_dev = dax_get_by_host(bdev->bd_disk->disk_name);
-        if (!dax_dev) {
-                vfs_msg(sb, KERN_ERR, "error: device does not support dax");
-                return -EOPNOTSUPP;
-        }
-
-        id = dax_read_lock();
-        len = dax_direct_access(dax_dev, pgoff, 1, &kaddr, &pfn);
-        dax_read_unlock(id);
-
-        put_dax(dax_dev);
-
-        if (len < 1) {
-                vfs_msg(sb, KERN_ERR,
-                                "error: dax access failed (%ld)", len);
-                return len < 0 ? len : -EIO;
-        }
-
-        return 0;
-}
-EXPORT_SYMBOL_GPL(bdev_dax_supported);
-
 /*
  * pseudo-fs
  */
diff --git a/fs/ext2/super.c b/fs/ext2/super.c
index 9e25a71fe1a2..d07773b81da9 100644
--- a/fs/ext2/super.c
+++ b/fs/ext2/super.c
@@ -32,6 +32,7 @@
 #include <linux/log2.h>
 #include <linux/quotaops.h>
 #include <linux/uaccess.h>
+#include <linux/dax.h>
 #include "ext2.h"
 #include "xattr.h"
 #include "acl.h"
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a9448db1cf7e..bf6bb8997124 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -37,6 +37,7 @@
 #include <linux/ctype.h>
 #include <linux/log2.h>
 #include <linux/crc16.h>
+#include <linux/dax.h>
 #include <linux/cleancache.h>
 #include <linux/uaccess.h>
 
diff --git a/fs/xfs/xfs_super.c b/fs/xfs/xfs_super.c
index 685c042a120f..f5c58d6dcafb 100644
--- a/fs/xfs/xfs_super.c
+++ b/fs/xfs/xfs_super.c
@@ -52,6 +52,7 @@
 #include "xfs_reflink.h"
 
 #include <linux/namei.h>
+#include <linux/dax.h>
 #include <linux/init.h>
 #include <linux/slab.h>
 #include <linux/mount.h>
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 848f87eb1905..e4d9899755a7 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1940,8 +1940,6 @@ extern int __blkdev_driver_ioctl(struct block_device *, fmode_t, unsigned int,
 extern int bdev_read_page(struct block_device *, sector_t, struct page *);
 extern int bdev_write_page(struct block_device *, sector_t, struct page *,
                                                 struct writeback_control *);
-extern int bdev_dax_supported(struct super_block *, int);
-int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
 #else /* CONFIG_BLOCK */
 
 struct block_device;
diff --git a/include/linux/dax.h b/include/linux/dax.h
index d3158e74a59e..7fdf1d710042 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -18,12 +18,38 @@ struct dax_operations {
                         void **, pfn_t *);
 };
 
+int bdev_dax_pgoff(struct block_device *, sector_t, size_t, pgoff_t *pgoff);
+#if IS_ENABLED(CONFIG_FS_DAX)
+int __bdev_dax_supported(struct super_block *sb, int blocksize);
+static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
+{
+        return __bdev_dax_supported(sb, blocksize);
+}
+#else
+static inline int bdev_dax_supported(struct super_block *sb, int blocksize)
+{
+        return -EOPNOTSUPP;
+}
+#endif
+
+#if IS_ENABLED(CONFIG_DAX)
+struct dax_device *dax_get_by_host(const char *host);
+void put_dax(struct dax_device *dax_dev);
+#else
+static inline struct dax_device *dax_get_by_host(const char *host)
+{
+        return NULL;
+}
+
+static inline void put_dax(struct dax_device *dax_dev)
+{
+}
+#endif
+
 int dax_read_lock(void);
 void dax_read_unlock(int id);
-struct dax_device *dax_get_by_host(const char *host);
 struct dax_device *alloc_dax(void *private, const char *host,
                 const struct dax_operations *ops);
-void put_dax(struct dax_device *dax_dev);
 bool dax_alive(struct dax_device *dax_dev);
 void kill_dax(struct dax_device *dax_dev);
 void *dax_get_private(struct dax_device *dax_dev);