[PATCH 08/10] iomap: New iomap_written operation

[Andreas Gruenbacher <agruenba@redhat.com>]

Add a callback to iomap_file_buffered_write that's called whenever
writing to a page has completed.  This is needed for implementing data
journaling: in the data journaling case, pages are written into the
journal before being written back to their proper on-disk locations.

(So far, the only user of iomap_file_buffered_write is xfs, which
doesn't do data journaling.)

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/iomap.c            | 21 +++++++++++++++++++--
 include/linux/iomap.h |  9 +++++++++
 2 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/fs/iomap.c b/fs/iomap.c
index 47d29ccffaef..98903be66c35 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -149,11 +149,21 @@ iomap_write_end(struct inode *inode, loff_t pos, unsigned len,
 	return ret;
 }
 
+struct iomap_write_data {
+	struct iov_iter *iter;
+	const struct iomap_ops *ops;
+};
+
 static loff_t
 iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 		struct iomap *iomap)
 {
-	struct iov_iter *i = data;
+	struct iomap_write_data *d = data;
+	struct iov_iter *i = d->iter;
+	void (*iomap_written)(struct inode *inode, struct page *page,
+			      unsigned int offset, unsigned int length,
+			      unsigned int written) =
+		d->ops->iomap_written;
 	long status = 0;
 	ssize_t written = 0;
 	unsigned int flags = AOP_FLAG_NOFS;
@@ -198,6 +208,9 @@ iomap_write_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 
 		flush_dcache_page(page);
 
+		if (iomap_written)
+			iomap_written(inode, page, offset, bytes, copied);
+
 		status = iomap_write_end(inode, pos, bytes, copied, page);
 		if (unlikely(status < 0))
 			break;
@@ -235,10 +248,14 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
 {
 	struct inode *inode = iocb->ki_filp->f_mapping->host;
 	loff_t pos = iocb->ki_pos, ret = 0, written = 0;
+	struct iomap_write_data data = {
+		.iter = iter,
+		.ops = ops,
+	};
 
 	while (iov_iter_count(iter)) {
 		ret = iomap_apply(inode, pos, iov_iter_count(iter),
-				IOMAP_WRITE, ops, iter, iomap_write_actor);
+				IOMAP_WRITE, ops, &data, iomap_write_actor);
 		if (ret <= 0)
 			break;
 		pos += ret;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 19a07de28212..042b8c8df44b 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -61,6 +61,8 @@ struct iomap {
 #define IOMAP_DIRECT		(1 << 4) /* direct I/O */
 #define IOMAP_NOWAIT		(1 << 5) /* Don't wait for writeback */
 
+struct page;
+
 struct iomap_ops {
 	/*
 	 * Return the existing mapping at pos, or reserve space starting at
@@ -70,6 +72,13 @@ struct iomap_ops {
 	int (*iomap_begin)(struct inode *inode, loff_t pos, loff_t length,
 			unsigned flags, struct iomap *iomap);
 
+	/*
+	 * Called after writing to a page has completed.
+	 */
+	void (*iomap_written)(struct inode *inode, struct page *page,
+			      unsigned int offset, unsigned int length,
+			      unsigned int written);
+
 	/*
 	 * Commit and/or unreserve space previous allocated using iomap_begin.
 	 * Written indicates the length of the successful write operation which
-- 
2.14.3