[PATCH 01/15] dax: export a low-level __dax_zero_page_range helper

Christoph Hellwig
2016-05-09T08:47:32Z

This allows XFS to perform zeroing using the iomap infrastructure and
avoid buffer heads.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
fs/dax.c | 35 ++++++++++++++++++++---------------
include/linux/dax.h | 7 +++++++
2 files changed, 27 insertions(+), 15 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 90322eb..6d5d744 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1082,6 +1082,23 @@ int dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
}
EXPORT_SYMBOL_GPL(dax_pfn_mkwrite);

+int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
+ unsigned int offset, unsigned int length)
+{
+ struct blk_dax_ctl dax = {
+ .sector = sector,
+ .size = PAGE_CACHE_SIZE,
+ };
+
+ if (dax_map_atomic(bdev, &dax) < 0)
+ return PTR_ERR(dax.addr);
+ clear_pmem(dax.addr + offset, length);
+ wmb_pmem();
+ dax_unmap_atomic(bdev, &dax);
+ return 0;
+}
+EXPORT_SYMBOL_GPL(__dax_zero_page_range);
+
/**
* dax_zero_page_range - zero a range within a page of a DAX file
* @inode: The file being truncated
@@ -1117,23 +1134,11 @@ int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
bh.b_bdev = inode->i_sb->s_bdev;
bh.b_size = PAGE_CACHE_SIZE;
err = get_block(inode, index, &bh, 0);
- if (err < 0)
+ if (err < 0 || !buffer_written(&bh))
return err;
- if (buffer_written(&bh)) {
- struct block_device *bdev = bh.b_bdev;
- struct blk_dax_ctl dax = {
- .sector = to_sector(&bh, inode),
- .size = PAGE_CACHE_SIZE,
- };

- if (dax_map_atomic(bdev, &dax) < 0)
- return PTR_ERR(dax.addr);
- clear_pmem(dax.addr + offset, length);
- wmb_pmem();
- dax_unmap_atomic(bdev, &dax);
- }
-
- return 0;
+ return __dax_zero_page_range(bh.b_bdev, to_sector(&bh, inode),
+ offset, length);
}
EXPORT_SYMBOL_GPL(dax_zero_page_range);

diff --git a/include/linux/dax.h b/include/linux/dax.h
index 636dd59..8155b81 100644
--- a/include/linux/dax.h
+++ b/include/linux/dax.h
@@ -17,12 +17,19 @@ int __dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t,

#ifdef CONFIG_FS_DAX
struct page *read_dax_sector(struct block_device *bdev, sector_t n);
+int __dax_zero_page_range(struct block_device *bdev, sector_t sector,
+ unsigned int offset, unsigned int length);
#else
static inline struct page *read_dax_sector(struct block_device *bdev,
sector_t n)
{
return ERR_PTR(-ENXIO);
}
+static inline int __dax_zero_page_range(struct block_device *bdev,
+ sector_t sector, unsigned int offset, unsigned int length)
+{
+ return -ENXIO;
+}
#endif

#ifdef CONFIG_TRANSPARENT_HUGEPAGE