Re: [PATCH 2/2] block: unify flags for struct bio and struct request

[Nick Piggin <npiggin@suse.de>]

On Fri, Jun 18, 2010 at 09:47:04AM +0200, Christoph Hellwig wrote:
> Remove the current bio flags and reuse the request flags for the bio, too.
> This allows to more easily trace the type of I/O from the filesystem
> down to the block driver.  There were two flags in the bio that were
> missing in the requests:  BIO_RW_UNPLUG and BIO_RW_AHEAD.  Also I've
> renamed two request flags that had a superflous RW in them.
> 
> Note that the flags are in bio.h despite having the REQ_ name - as
> blkdev.h includes bio.h that is the only way to go for now.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> 
> Index: linux-2.6/block/blk-core.c
> ===================================================================
> --- linux-2.6.orig/block/blk-core.c	2010-06-17 13:21:18.000000000 +0200
> +++ linux-2.6/block/blk-core.c	2010-06-17 13:26:55.958005535 +0200
> @@ -1139,27 +1139,9 @@ void init_request_from_bio(struct reques
>  {
>  	req->cpu = bio->bi_comp_cpu;
>  	req->cmd_type = REQ_TYPE_FS;
> -
> -	/*
> -	 * Inherit FAILFAST from bio (for read-ahead, and explicit
> -	 * FAILFAST).  FAILFAST flags are identical for req and bio.
> -	 */
> -	if (bio_rw_flagged(bio, BIO_RW_AHEAD))
> +	req->cmd_flags |= bio->bi_rw & REQ_COMMON_MASK;
> +	if (bio->bi_rw & REQ_RAHEAD)
>  		req->cmd_flags |= REQ_FAILFAST_MASK;
> -	else
> -		req->cmd_flags |= bio->bi_rw & REQ_FAILFAST_MASK;
> -
> -	if (bio_rw_flagged(bio, BIO_RW_DISCARD))
> -		req->cmd_flags |= REQ_DISCARD;
> -	if (bio_rw_flagged(bio, BIO_RW_BARRIER))
> -		req->cmd_flags |= REQ_HARDBARRIER;
> -	if (bio_rw_flagged(bio, BIO_RW_SYNCIO))
> -		req->cmd_flags |= REQ_RW_SYNC;
> -	if (bio_rw_flagged(bio, BIO_RW_META))
> -		req->cmd_flags |= REQ_RW_META;
> -	if (bio_rw_flagged(bio, BIO_RW_NOIDLE))
> -		req->cmd_flags |= REQ_NOIDLE;

Much better for branches and icache.

Any reason not to make REQ_RAHEAD include REQ_FAILFAST_MASK?