From d1a5f2b4d8a125943dcb6b032fc7eaefc2c78296 Mon Sep 17 00:00:00 2001
From: Dan Williams <dan.j.williams@intel.com>
Date: Thu, 28 Jan 2016 20:25:31 -0800
Subject: block: use DAX for partition table reads

Avoid populating pagecache when the block device is in DAX mode.
Otherwise these page cache entries collide with the fsync/msync
implementation and break data durability guarantees.

Cc: Jan Kara <jack@suse.com>
Cc: Jeff Moyer <jmoyer@redhat.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Dave Chinner <david@fromorbit.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Reported-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Tested-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Matthew Wilcox <willy@linux.intel.com>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
---
 fs/dax.c | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)

(limited to 'fs')

diff --git a/fs/dax.c b/fs/dax.c
index 4fd6b0c5c6b5..e0e9358baf35 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -58,6 +58,26 @@ static void dax_unmap_atomic(struct block_device *bdev,
 	blk_queue_exit(bdev->bd_queue);
 }
 
+struct page *read_dax_sector(struct block_device *bdev, sector_t n)
+{
+	struct page *page = alloc_pages(GFP_KERNEL, 0);
+	struct blk_dax_ctl dax = {
+		.size = PAGE_SIZE,
+		.sector = n & ~((((int) PAGE_SIZE) / 512) - 1),
+	};
+	long rc;
+
+	if (!page)
+		return ERR_PTR(-ENOMEM);
+
+	rc = dax_map_atomic(bdev, &dax);
+	if (rc < 0)
+		return ERR_PTR(rc);
+	memcpy_from_pmem(page_address(page), dax.addr, PAGE_SIZE);
+	dax_unmap_atomic(bdev, &dax);
+	return page;
+}
+
 /*
  * dax_clear_blocks() is called from within transaction context from XFS,
  * and hence this means the stack from this point must follow GFP_NOFS
-- 
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