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>
diff --git a/fs/dax.c b/fs/dax.c
index 4fd6b0c..e0e9358 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -58,6 +58,26 @@
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