[PATCH 1/7] block: add support for carrying a stream ID in a bio

[Jens Axboe <axboe@fb.com>]

The top bits of bio->bi_flags are reserved for keeping the
allocation pool, set aside the next eight bits for carrying
a stream ID. That leaves us with support for 255 streams,
0 is reserved as a "stream not set" value.

Add helpers for setting/getting stream ID of a bio.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 block/bio.c               |  2 ++
 block/blk-core.c          |  3 +++
 include/linux/blk_types.h | 28 +++++++++++++++++++++++++++-
 3 files changed, 32 insertions(+), 1 deletion(-)

diff --git a/block/bio.c b/block/bio.c
index f66a4eae16ee..1cd3d745047c 100644
--- a/block/bio.c
+++ b/block/bio.c
@@ -567,6 +567,7 @@ void __bio_clone_fast(struct bio *bio, struct bio *bio_src)
 	bio->bi_rw = bio_src->bi_rw;
 	bio->bi_iter = bio_src->bi_iter;
 	bio->bi_io_vec = bio_src->bi_io_vec;
+	bio_set_streamid(bio, bio_get_streamid(bio_src));
 }
 EXPORT_SYMBOL(__bio_clone_fast);
 
@@ -672,6 +673,7 @@ integrity_clone:
 		}
 	}
 
+	bio_set_streamid(bio, bio_get_streamid(bio_src));
 	return bio;
 }
 EXPORT_SYMBOL(bio_clone_bioset);
diff --git a/block/blk-core.c b/block/blk-core.c
index 794c3e7f01cf..6b7b8c95c4c3 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1928,6 +1928,9 @@ void generic_make_request(struct bio *bio)
 	do {
 		struct request_queue *q = bdev_get_queue(bio->bi_bdev);
 
+		if (bio_streamid_valid(bio))
+			blk_add_trace_msg(q, "StreamID=%u", bio_get_streamid(bio));
+
 		q->make_request_fn(q, bio);
 
 		bio = bio_list_pop(current->bio_list);
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index c294e3e25e37..d6909007a3fe 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -138,9 +138,35 @@ struct bio {
 #define BIO_POOL_BITS		(4)
 #define BIO_POOL_NONE		((1UL << BIO_POOL_BITS) - 1)
 #define BIO_POOL_OFFSET		(BITS_PER_LONG - BIO_POOL_BITS)
-#define BIO_POOL_MASK		(1UL << BIO_POOL_OFFSET)
 #define BIO_POOL_IDX(bio)	((bio)->bi_flags >> BIO_POOL_OFFSET)
 
+/*
+ * after the pool bits, next 8 bits are for the stream id
+ */
+#define BIO_STREAM_BITS		(8)
+#define BIO_STREAM_OFFSET	(BITS_PER_LONG - 12)
+#define BIO_STREAM_MASK		((1 << BIO_STREAM_BITS) - 1)
+
+static inline unsigned long streamid_to_flags(unsigned int id)
+{
+	return (unsigned long) (id & BIO_STREAM_MASK) << BIO_STREAM_OFFSET;
+}
+
+static inline void bio_set_streamid(struct bio *bio, unsigned int id)
+{
+	bio->bi_flags |= streamid_to_flags(id);
+}
+
+static inline unsigned int bio_get_streamid(struct bio *bio)
+{
+	return (bio->bi_flags >> BIO_STREAM_OFFSET) & BIO_STREAM_MASK;
+}
+
+static inline bool bio_streamid_valid(struct bio *bio)
+{
+	return bio_get_streamid(bio) != 0;
+}
+
 #endif /* CONFIG_BLOCK */
 
 /*
-- 
1.9.1