iomap: implement direct I/O

This adds a full fledget direct I/O implementation using the iomap
interface. Full fledged in this case means all features are supported:
AIO, vectored I/O, any iov_iter type including kernel pointers, bvecs
and pipes, support for hole filling and async apending writes.  It does
not mean supporting all the warts of the old generic code.  We expect
i_rwsem to be held over the duration of the call, and we expect to
maintain i_dio_count ourselves, and we pass on any kinds of mapping
to the file system for now.

The algorithm used is very simple: We use iomap_apply to iterate over
the range of the I/O, and then we use the new bio_iov_iter_get_pages
helper to lock down the user range for the size of the extent.
bio_iov_iter_get_pages can currently lock down twice as many pages as
the old direct I/O code did, which means that we will have a better
batch factor for everything but overwrites of badly fragmented files.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Kent Overstreet <kent.overstreet@gmail.com>
Tested-by: Jens Axboe <axboe@fb.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

1 files changed, 11 insertions, 0 deletions

diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index f185156de74d..a4c94b86401e 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -50,6 +50,7 @@ struct iomap {
 #define IOMAP_ZERO		(1 << 1) /* zeroing operation, may skip holes */
 #define IOMAP_REPORT		(1 << 2) /* report extent status, e.g. FIEMAP */
 #define IOMAP_FAULT		(1 << 3) /* mapping for page fault */
+#define IOMAP_DIRECT		(1 << 4) /* direct I/O */
 
 struct iomap_ops {
 	/*
@@ -83,4 +84,14 @@ int iomap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 int iomap_fiemap(struct inode *inode, struct fiemap_extent_info *fieinfo,
 		loff_t start, loff_t len, struct iomap_ops *ops);
 
+/*
+ * Flags for direct I/O ->end_io:
+ */
+#define IOMAP_DIO_UNWRITTEN	(1 << 0)	/* covers unwritten extent(s) */
+#define IOMAP_DIO_COW		(1 << 1)	/* covers COW extent(s) */
+typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
+		unsigned flags);
+ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
+		struct iomap_ops *ops, iomap_dio_end_io_t end_io);
+
 #endif /* LINUX_IOMAP_H */