[PATCH 5/5] iomap: support RWF_UNCACHED for buffered writes

[Jens Axboe <axboe@kernel.dk>]

This adds support for RWF_UNCACHED for file systems using iomap to
perform buffered writes. We use the generic infrastructure for this,
by tracking pages we created and calling write_drop_cached_pages()
to issue writeback and prune those pages.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/iomap/apply.c       | 24 ++++++++++++++++++++++++
 fs/iomap/buffered-io.c | 23 +++++++++++++++++++----
 include/linux/iomap.h  |  5 +++++
 3 files changed, 48 insertions(+), 4 deletions(-)

diff --git a/fs/iomap/apply.c b/fs/iomap/apply.c
index e76148db03b8..11b6812f7b37 100644
--- a/fs/iomap/apply.c
+++ b/fs/iomap/apply.c
@@ -92,5 +92,29 @@ iomap_apply(struct iomap_data *data, const struct iomap_ops *ops,
 				     data->flags, &iomap);
 	}
 
+	if (written && (data->flags & IOMAP_UNCACHED)) {
+		struct address_space *mapping = data->inode->i_mapping;
+
+		end = data->pos + written;
+		ret = filemap_write_and_wait_range(mapping, data->pos, end);
+		if (ret)
+			goto out;
+
+		/*
+		 * No pages were created for this range, we're done
+		 */
+		if (!(iomap.flags & IOMAP_F_PAGE_CREATE))
+			goto out;
+
+		/*
+		 * Try to invalidate cache pages for the range we just wrote.
+		 * We don't care if invalidation fails as the write has still
+		 * worked and leaving clean uptodate pages in the page cache
+		 * isn't a corruption vector for uncached IO.
+		 */
+		invalidate_inode_pages2_range(mapping,
+				data->pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
+	}
+out:
 	return written ? written : ret;
 }
diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
index 0a1a195ed1cc..df9d6002858e 100644
--- a/fs/iomap/buffered-io.c
+++ b/fs/iomap/buffered-io.c
@@ -659,6 +659,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
 		struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
 {
 	const struct iomap_page_ops *page_ops = iomap->page_ops;
+	unsigned aop_flags;
 	struct page *page;
 	int status = 0;
 
@@ -675,8 +676,11 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
 			return status;
 	}
 
+	aop_flags = AOP_FLAG_NOFS;
+	if (flags & IOMAP_UNCACHED)
+		aop_flags |= AOP_FLAG_UNCACHED;
 	page = grab_cache_page_write_begin(inode->i_mapping, pos >> PAGE_SHIFT,
-			AOP_FLAG_NOFS);
+						aop_flags);
 	if (!page) {
 		status = -ENOMEM;
 		goto out_no_page;
@@ -818,6 +822,7 @@ iomap_write_actor(const struct iomap_data *data, struct iomap *iomap,
 {
 	struct inode *inode = data->inode;
 	struct iov_iter *i = data->priv;
+	unsigned flags = data->flags;
 	loff_t length = data->len;
 	loff_t pos = data->pos;
 	long status = 0;
@@ -851,10 +856,17 @@ iomap_write_actor(const struct iomap_data *data, struct iomap *iomap,
 			break;
 		}
 
-		status = iomap_write_begin(inode, pos, bytes, 0, &page, iomap,
-				srcmap);
-		if (unlikely(status))
+retry:
+		status = iomap_write_begin(inode, pos, bytes, flags,
+						&page, iomap, srcmap);
+		if (unlikely(status)) {
+			if (status == -ENOMEM && (flags & IOMAP_UNCACHED)) {
+				iomap->flags |= IOMAP_F_PAGE_CREATE;
+				flags &= ~IOMAP_UNCACHED;
+				goto retry;
+			}
 			break;
+		}
 
 		if (mapping_writably_mapped(inode->i_mapping))
 			flush_dcache_page(page);
@@ -907,6 +919,9 @@ iomap_file_buffered_write(struct kiocb *iocb, struct iov_iter *iter,
 	};
 	loff_t ret = 0, written = 0;
 
+	if (iocb->ki_flags & IOCB_UNCACHED)
+		data.flags |= IOMAP_UNCACHED;
+
 	while (iov_iter_count(iter)) {
 		data.len = iov_iter_count(iter);
 		ret = iomap_apply(&data, ops, iomap_write_actor);
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 30f40145a9e9..30bb248e1d0d 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -48,12 +48,16 @@ struct vm_fault;
  *
  * IOMAP_F_BUFFER_HEAD indicates that the file system requires the use of
  * buffer heads for this mapping.
+ *
+ * IOMAP_F_PAGE_CREATE indicates that pages had to be allocated to satisfy
+ * this operation.
  */
 #define IOMAP_F_NEW		0x01
 #define IOMAP_F_DIRTY		0x02
 #define IOMAP_F_SHARED		0x04
 #define IOMAP_F_MERGED		0x08
 #define IOMAP_F_BUFFER_HEAD	0x10
+#define IOMAP_F_PAGE_CREATE	0x20
 
 /*
  * Flags set by the core iomap code during operations:
@@ -121,6 +125,7 @@ struct iomap_page_ops {
 #define IOMAP_FAULT		(1 << 3) /* mapping for page fault */
 #define IOMAP_DIRECT		(1 << 4) /* direct I/O */
 #define IOMAP_NOWAIT		(1 << 5) /* do not block */
+#define IOMAP_UNCACHED		(1 << 6)
 
 struct iomap_ops {
 	/*
-- 
2.24.1