[PATCH 09/15] block: expose write streams for block device nodes

[Christoph Hellwig]

Export statx information about the number and granularity of write
streams, use the per-kiocb write hint and map temperature hints
to write streams (which is a bit questionable, but this shows how it is
done).

Signed-off-by: Christoph Hellwig <hch at lst.de>
---
 block/bdev.c |  6 ++++++
 block/fops.c | 23 +++++++++++++++++++++++
 2 files changed, 29 insertions(+)

diff --git a/block/bdev.c b/block/bdev.c
index 738e3c8457e7..c23245f1fdfe 100644
--- a/block/bdev.c
+++ b/block/bdev.c
@@ -1296,6 +1296,12 @@ void bdev_statx(struct path *path, struct kstat *stat,
 		stat->result_mask |= STATX_DIOALIGN;
 	}
 
+	if ((request_mask & STATX_WRITE_STREAM) &&
+	    bdev_max_write_streams(bdev)) {
+		stat->write_stream_max = bdev_max_write_streams(bdev);
+		stat->result_mask |= STATX_WRITE_STREAM;
+	}
+
 	if (request_mask & STATX_WRITE_ATOMIC && bdev_can_atomic_write(bdev)) {
 		struct request_queue *bd_queue = bdev->bd_queue;
 
diff --git a/block/fops.c b/block/fops.c
index 2d01c9007681..2a860dbe5e48 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -72,6 +72,7 @@ static ssize_t __blkdev_direct_IO_simple(struct kiocb *iocb,
 	}
 	bio.bi_iter.bi_sector = pos >> SECTOR_SHIFT;
 	bio.bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
+	bio.bi_write_stream = iocb->ki_write_stream;
 	bio.bi_ioprio = iocb->ki_ioprio;
 	if (iocb->ki_flags & IOCB_ATOMIC)
 		bio.bi_opf |= REQ_ATOMIC;
@@ -201,6 +202,7 @@ static ssize_t __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter,
 	for (;;) {
 		bio->bi_iter.bi_sector = pos >> SECTOR_SHIFT;
 		bio->bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
+		bio->bi_write_stream = iocb->ki_write_stream;
 		bio->bi_private = dio;
 		bio->bi_end_io = blkdev_bio_end_io;
 		bio->bi_ioprio = iocb->ki_ioprio;
@@ -317,6 +319,7 @@ static ssize_t __blkdev_direct_IO_async(struct kiocb *iocb,
 	dio->iocb = iocb;
 	bio->bi_iter.bi_sector = pos >> SECTOR_SHIFT;
 	bio->bi_write_hint = file_inode(iocb->ki_filp)->i_write_hint;
+	bio->bi_write_stream = iocb->ki_write_stream;
 	bio->bi_end_io = blkdev_bio_end_io_async;
 	bio->bi_ioprio = iocb->ki_ioprio;
 
@@ -373,6 +376,26 @@ static ssize_t blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 	if (blkdev_dio_invalid(bdev, iocb, iter))
 		return -EINVAL;
 
+	if (iov_iter_rw(iter) == WRITE) {
+		u16 max_write_streams = bdev_max_write_streams(bdev);
+
+		if (iocb->ki_write_stream) {
+			if (iocb->ki_write_stream > max_write_streams)
+				return -EINVAL;
+		} else if (max_write_streams) {
+			enum rw_hint write_hint =
+				file_inode(iocb->ki_filp)->i_write_hint;
+
+			/*
+			 * Just use the write hint as write stream for block
+			 * device writes.  This assumes no file system is
+			 * mounted that would use the streams differently.
+			 */
+			if (write_hint <= max_write_streams)
+				iocb->ki_write_stream = write_hint;
+		}
+	}
+
 	nr_pages = bio_iov_vecs_to_alloc(iter, BIO_MAX_VECS + 1);
 	if (likely(nr_pages <= BIO_MAX_VECS)) {
 		if (is_sync_kiocb(iocb))
-- 
2.45.2