This new function allows us to support hole-punch for DAX files by zeroing
a partial page, as opposed to the dax_truncate_page() function which can
only truncate to the end of the page. Reimplement dax_truncate_page() to
call dax_zero_page_range().
Signed-off-by: Matthew Wilcox <matthew.r.wilcox@xxxxxxxxx>
[ported to 3.13-rc2]
Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx>
---
Documentation/filesystems/dax.txt | 1 +
fs/dax.c | 36 +++++++++++++++++++++++++++++++-----
include/linux/fs.h | 1 +
3 files changed, 33 insertions(+), 5 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 e838ec8..24f6e14 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -460,13 +460,16 @@ 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
@@ -474,17 +477,18 @@ 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 */
if (!length)
return 0;
+ BUG_ON((offset + length) > PAGE_CACHE_SIZE);
memset(&bh, 0, sizeof(bh));
bh.b_size = PAGE_CACHE_SIZE;
@@ -501,4 +505,26 @@ int dax_truncate_page(struct inode *inode, loff_t from, get_block_t get_block)
return 0;
}
+EXPORT_SYMBOL_GPL(dax_zero_page_range);
+
+/**
+ * dax_truncate_page - handle a partial page being truncated in a DAX file
+ * @inode: The file being truncated
+ * @from: The file offset that is being truncated to
+ * @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.
+ *
+ * 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
+ * took care of disposing of the unnecessary blocks. Even if the filesystem
+ * 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)
+{
+ unsigned length = PAGE_CACHE_ALIGN(from) - from;
+ return dax_zero_page_range(inode, from, length, get_block);
+}
EXPORT_SYMBOL_GPL(dax_truncate_page);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index dad6628..563a6ca 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -2474,6 +2474,7 @@ extern int nonseekable_open(struct inode * inode, struct file * filp);
ssize_t dax_do_io(int rw, struct kiocb *, struct inode *, struct iov_iter *,
loff_t, get_block_t, dio_iodone_t, int flags);
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);
int dax_fault(struct vm_area_struct *, struct vm_fault *, get_block_t);
#define dax_mkwrite(vma, vmf, gb) dax_fault(vma, vmf, gb)
--
2.1.1
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