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

Toshi Kani
2016-05-10T16:33:09Z

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 <toshi.kani@hpe.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Alexander Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@fb.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>
Cc: Andreas Dilger <adilger.kernel@dilger.ca>
Cc: Jan Kara <jack@suse.cz>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Boaz Harrosh <boaz@plexistor.com>
---
fs/block_dev.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 1 +
2 files changed, 46 insertions(+)

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;