linux-kernel - [PATCH v2 1/3] ext4: Add alignment check for DAX mount

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Date:	Mon,  2 May 2016 12:42:56 -0600
From:	Toshi Kani <toshi.kani@....com>
To:	dan.j.williams@...el.com, jack@...e.cz, david@...morbit.com
Cc:	hch@...radead.org, boaz@...xistor.com, tytso@....edu,
	adilger.kernel@...ger.ca, ross.zwisler@...ux.intel.com,
	toshi.kani@....com, micah.parrish@....com,
	linux-nvdimm@...ts.01.org, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: [PATCH v2 1/3] ext4: Add alignment check for DAX mount

When a partition is not aligned by 4KB, mount -o dax succeeds,
but any read/write access to the filesystem fails, except for
metadata update.

Call bdev_direct_access to check the alignment when -o dax is
specified.

Reported-by: Micah Parrish <micah.parrish@....com>
Signed-off-by: Toshi Kani <toshi.kani@....com>
Cc: "Theodore Ts'o" <tytso@....edu>
Cc: Andreas Dilger <adilger.kernel@...ger.ca>
Cc: Jan Kara <jack@...e.cz>
Cc: Dan Williams <dan.j.williams@...el.com>
Cc: Ross Zwisler <ross.zwisler@...ux.intel.com>
Cc: Christoph Hellwig <hch@...radead.org>
Cc: Boaz Harrosh <boaz@...xistor.com>
---
 fs/ext4/super.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 304c712..51ac78e 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -3416,14 +3416,30 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 	}
 
 	if (sbi->s_mount_opt & EXT4_MOUNT_DAX) {
+		struct blk_dax_ctl dax = {
+			.sector = 0,
+			.size = PAGE_SIZE,
+		};
 		if (blocksize != PAGE_SIZE) {
 			ext4_msg(sb, KERN_ERR,
 					"error: unsupported blocksize for dax");
 			goto failed_mount;
 		}
-		if (!sb->s_bdev->bd_disk->fops->direct_access) {
-			ext4_msg(sb, KERN_ERR,
+		err = bdev_direct_access(sb->s_bdev, &dax);
+		if (err < 0) {
+			switch (err) {
+			case -EOPNOTSUPP:
+				ext4_msg(sb, KERN_ERR,
 					"error: device does not support dax");
+				break;
+			case -EINVAL:
+				ext4_msg(sb, KERN_ERR,
+					"error: unaligned partition for dax");
+				break;
+			default:
+				ext4_msg(sb, KERN_ERR,
+					"error: dax access failed (%d)", err);
+			}
 			goto failed_mount;
 		}
 	}