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Commit dbde775c authored by NeilBrown's avatar NeilBrown Committed by Jens Axboe
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block: simple improvements for bio->flags 



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: default avatarNeilBrown <neilb@suse.com>
Signed-off-by: default avatarJens Axboe <axboe@fb.com>
parent 1dd5198b

include/linux/blk_types.h

+13 −9
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ 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;
@@ -110,12 +110,7 @@ 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
@@ -125,13 +120,22 @@ 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.