[v4,2/6] block: Add bdev_dax_supported() for dax mount checks

Commit Message

Kani, Toshi May 10, 2016, 4:23 p.m. UTC

DAX imposes additional requirements to a device.  Add
bdev_dax_supported() which performs all the precondition checks
necessary for filesystem to mount the device with dax option.

Also add a new check to verify if a partition is aligned by 4KB.
When a partition is unaligned, any dax read/write access fails,
except for metadata update.

Signed-off-by: Toshi Kani <[e-mail]>
Reviewed-by: Christoph Hellwig <[e-mail]>
Cc: Alexander Viro <[e-mail]>
Cc: Jens Axboe <[e-mail]>
Cc: "Theodore Ts'o" <[e-mail]>
Cc: Andreas Dilger <[e-mail]>
Cc: Jan Kara <[e-mail]>
Cc: Dave Chinner <[e-mail]>
Cc: Dan Williams <[e-mail]>
Cc: Ross Zwisler <[e-mail]>
Cc: Christoph Hellwig <[e-mail]>
Cc: Boaz Harrosh <[e-mail]>
---
 fs/block_dev.c         |   45 +++++++++++++++++++++++++++++++++++++++++++++
 include/linux/blkdev.h |    1 +
 2 files changed, 46 insertions(+)

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Patch

diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7be17c4..db55638 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -509,6 +509,51 @@  long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
 }
 EXPORT_SYMBOL_GPL(bdev_direct_access);
 
+/**
+ * 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 blk_dax_ctl dax = {
+		.sector = 0,
+		.size = PAGE_SIZE,
+	};
+	int err;
+
+	if (blocksize != PAGE_SIZE) {
+		vfs_msg(sb, KERN_ERR, "error: unsupported blocksize for dax");
+		return -EINVAL;
+	}
+
+	err = bdev_direct_access(sb->s_bdev, &dax);
+	if (err < 0) {
+		switch (err) {
+		case -EOPNOTSUPP:
+			vfs_msg(sb, KERN_ERR,
+				"error: device does not support dax");
+			break;
+		case -EINVAL:
+			vfs_msg(sb, KERN_ERR,
+				"error: unaligned partition for dax");
+			break;
+		default:
+			vfs_msg(sb, KERN_ERR,
+				"error: dax access failed (%d)", err);
+		}
+		return err;
+	}
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(bdev_dax_supported);
+
 /*
  * pseudo-fs
  */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 78c48ab..71231a5 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1688,6 +1688,7 @@  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 long bdev_direct_access(struct block_device *, struct blk_dax_ctl *);
+extern int bdev_dax_supported(struct super_block *, int);
 #else /* CONFIG_BLOCK */
 
 struct block_device;