[PATCH 10/11] iomap: add a IOMAP_DIO_UNALIGNED flag

[Christoph Hellwig <hch@lst.de>]

Add a flag to signal an I/O that is not file system block aligned.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 fs/iomap/direct-io.c  | 7 +++++++
 include/linux/iomap.h | 8 ++++++++
 2 files changed, 15 insertions(+)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 32dbbf7dd4aadb..d93019ee4c9e3e 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -485,6 +485,13 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		iomap_flags |= IOMAP_NOWAIT;
 	}
 
+	if (dio_flags & IOMAP_DIO_UNALIGNED) {
+		ret = -EAGAIN;
+		if (pos >= dio->i_size)
+			goto out_free_dio;
+		iomap_flags |= IOMAP_UNALIGNED;
+	}
+
 	ret = filemap_write_and_wait_range(mapping, pos, end);
 	if (ret)
 		goto out_free_dio;
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index b322598dc10ec0..2fa94ec9583d0a 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -122,6 +122,7 @@ 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_UNALIGNED		(1 << 6) /* do not allocate blocks */
 
 struct iomap_ops {
 	/*
@@ -262,6 +263,13 @@ struct iomap_dio_ops {
  */
 #define IOMAP_DIO_FORCE_WAIT	(1 << 0)
 
+/*
+ * Direct I/O that is not aligned to the file system block.  Do not allocate
+ * blocks and do not zero partial blocks, fall back to the caller by returning
+ * -EAGAIN instead.
+ */
+#define IOMAP_DIO_UNALIGNED	(1 << 1)
+
 ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, const struct iomap_dio_ops *dops,
 		unsigned int flags);
-- 
2.29.2