[PATCH v10 19/21] xip: Add xip_zero_page_range

Matthew Wilcox
2014-08-27T04:35:29Z

This new function allows us to support hole-punch for XIP files by zeroing
a partial page, as opposed to the xip_truncate_page() function which can
only truncate to the end of the page. Reimplement xip_truncate_page() as
a macro that calls xip_zero_page_range().

Signed-off-by: Matthew Wilcox <matthew.r.wilcox@intel.com>
[ported to 3.13-rc2]
Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
Documentation/filesystems/dax.txt | 1 +
fs/dax.c | 20 ++++++++++++++------
include/linux/fs.h | 9 ++++++++-
3 files changed, 23 insertions(+), 7 deletions(-)

diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt
index 635adaa..ebcd97f 100644
--- a/Documentation/filesystems/dax.txt
+++ b/Documentation/filesystems/dax.txt
@@ -62,6 +62,7 @@ Filesystem support consists of
for fault and page_mkwrite (which should probably call dax_fault() and
dax_mkwrite(), passing the appropriate get_block() callback)
- calling dax_truncate_page() instead of block_truncate_page() for DAX files
+- calling dax_zero_page_range() instead of zero_user() for DAX files
- ensuring that there is sufficient locking between reads, writes,
truncates and page faults

diff --git a/fs/dax.c b/fs/dax.c
index d54f7d3..96c4fed 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -445,13 +445,16 @@ int dax_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
EXPORT_SYMBOL_GPL(dax_fault);

/**
- * dax_truncate_page - handle a partial page being truncated in a DAX file
+ * dax_zero_page_range - zero a range within a page of a DAX file
* @inode: The file being truncated
* @from: The file offset that is being truncated to
+ * @length: The number of bytes to zero
* @get_block: The filesystem method used to translate file offsets to blocks
*
- * Similar to block_truncate_page(), this function can be called by a
- * filesystem when it is truncating an DAX file to handle the partial page.
+ * This function can be called by a filesystem when it is zeroing part of a
+ * page in a DAX file. This is intended for hole-punch operations. If
+ * you are truncating a file, the helper function dax_truncate_page() may be
+ * more convenient.
*
* We work in terms of PAGE_CACHE_SIZE here for commonality with
* block_truncate_page(), but we could go down to PAGE_SIZE if the filesystem
@@ -459,12 +462,12 @@ EXPORT_SYMBOL_GPL(dax_fault);
* block size is smaller than PAGE_SIZE, we have to zero the rest of the page
* since the file might be mmaped.
*/
-int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
+int dax_zero_page_range(struct inode *inode, loff_t from, unsigned length,
+ get_block_t get_block)
{
struct buffer_head bh;
pgoff_t index = from >> PAGE_CACHE_SHIFT;
unsigned offset = from & (PAGE_CACHE_SIZE-1);
- unsigned length = PAGE_CACHE_ALIGN(from) - from;
int err;

/* Block boundary? Nothing to do */
@@ -481,9 +484,14 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
err = dax_get_addr(&bh, &addr, inode->i_blkbits);
if (err < 0)
return err;
+ /*
+ * ext4 sometimes asks to zero past the end of a block. It
+ * really just wants to zero to the end of the block.
+ */
+ length = min_t(unsigned, length, PAGE_CACHE_SIZE - offset);
memset(addr + offset, 0, length);
}

return 0;
}
-EXPORT_SYMBOL_GPL(dax_truncate_page);
+EXPORT_SYMBOL_GPL(dax_zero_page_range);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index e6b48cc..b0078df 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2490,6 +2490,7 @@ extern int nonseekable_open(struct inode * inode, struct file * filp);

#ifdef CONFIG_FS_DAX
int dax_clear_blocks(struct inode *, sector_t block, long size);
+int dax_zero_page_range(struct inode *, loff_t from, unsigned len, get_block_t);
int dax_truncate_page(struct inode *, loff_t from, get_block_t);
ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, struct iov_iter *,
loff_t, get_block_t, dio_iodone_t, int flags);
@@ -2501,7 +2502,8 @@ static inline int dax_clear_blocks(struct inode *i, sector_t blk, long sz)
return 0;
}

-static inline int dax_truncate_page(struct inode *i, loff_t frm, get_block_t gb)
+static inline int dax_zero_page_range(struct inode *inode, loff_t from,
+ unsigned len, get_block_t gb)
{
return 0;
}
@@ -2514,6 +2516,11 @@ static inline ssize_t dax_do_io(int rw, struct kiocb *iocb,
}
#endif

+/* Can't be a function because PAGE_CACHE_SIZE is defined in pagemap.h */
+#define dax_truncate_page(inode, from, get_block) \
+ dax_zero_page_range(inode, from, PAGE_CACHE_SIZE, get_block)
+
+
#ifdef CONFIG_BLOCK
typedef void (dio_submit_t)(int rw, struct bio *bio, struct inode *inode,
loff_t file_offset);
--
2.0.0