The comment for the 'flags' field of 'bio' mentions
"command" which is no longer stored there, and doesn't
mention the bvec pool number, which is.
BIO_RESET_BITS is set in such a way that it would need to be
updated if new bits were added, which is easy to miss.
BVEC_POOL_BITS is larger than needed. The BVEC_POOL_IDX()
ranges from 0 to 6, so 3 bits are sufficient.
This patch make improvements in each of these areas.
Signed-off-by: NeilBrown <neilb@xxxxxxxx>
---
include/linux/blk_types.h | 22 +++++++++++++---------
1 file changed, 13 insertions(+), 9 deletions(-)
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index d703acb55d0f..ff07d891f38f 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -29,7 +29,7 @@ struct bio {
* top bits REQ_OP. Use
* accessors.
*/
- unsigned short bi_flags; /* status, command, etc */
+ unsigned short bi_flags; /* status, etc and bvec pool number */
unsigned short bi_ioprio;
struct bvec_iter bi_iter;
@@ -102,12 +102,7 @@ struct bio {
#define BIO_REFFED 8 /* bio has elevated ->bi_cnt */
#define BIO_THROTTLED 9 /* This bio has already been subjected to
* throttling rules. Don't do it again. */
-
-/*
- * Flags starting here get preserved by bio_reset() - this includes
- * BVEC_POOL_IDX()
- */
-#define BIO_RESET_BITS 10
+/* See BVEC_POOL_OFFSET below before adding new flags */
/*
* We support 6 different bvec pools, the last one is magic in that it
@@ -117,13 +112,22 @@ struct bio {
#define BVEC_POOL_MAX (BVEC_POOL_NR - 1)
/*
- * Top 4 bits of bio flags indicate the pool the bvecs came from. We add
+ * Top 3 bits of bio flags indicate the pool the bvecs came from. We add
* 1 to the actual index so that 0 indicates that there are no bvecs to be
* freed.
*/
-#define BVEC_POOL_BITS (4)
+#define BVEC_POOL_BITS (3)
#define BVEC_POOL_OFFSET (16 - BVEC_POOL_BITS)
#define BVEC_POOL_IDX(bio) ((bio)->bi_flags >> BVEC_POOL_OFFSET)
+#if (1<< BVEC_POOL_BITS) < (BVEC_POOL_NR+1)
+# error "BVEC_POOL_BITS is too small"
+#endif
+
+/*
+ * Flags starting here get preserved by bio_reset() - this includes
+ * only BVEC_POOL_IDX()
+ */
+#define BIO_RESET_BITS BVEC_POOL_OFFSET
/*
* Operations and flags common to the bio and request structures.
