DAX imposes additional requirements to a device. Add
bdev_supports_dax() 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@xxxxxxx>
Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Jens Axboe <axboe@xxxxxx>
Cc: "Theodore Ts'o" <tytso@xxxxxxx>
Cc: Andreas Dilger <adilger.kernel@xxxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
Cc: Christoph Hellwig <hch@xxxxxxxxxxxxx>
Cc: Boaz Harrosh <boaz@xxxxxxxxxxxxx>
---
fs/block_dev.c | 42 ++++++++++++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 1 +
2 files changed, 43 insertions(+)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 7be17c4..e51a2c3 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -509,6 +509,48 @@ long bdev_direct_access(struct block_device *bdev, struct blk_dax_ctl *dax)
}
EXPORT_SYMBOL_GPL(bdev_direct_access);
+/**
+ * bdev_supports_dax() - Check if the block device supports DAX
+ * @sb: The superblock of the device
+ * @blocksize: The block size of the device
+ *
+ * Return: negative errno if unsupported, 0 if supported.
+ */
+int bdev_supports_dax(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_supports_dax);
+
/*
* pseudo-fs
*/
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 78c48ab..6a792aa 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_supports_dax(struct super_block *, int);
#else /* CONFIG_BLOCK */
struct block_device;
--
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