Re: [PATCH] blktrace: readahead support

[Milton Miller]

Looking at the commit 

Date: Thu, 6 Jul 2006 08:03:28 +0000 (+0200)
X-Git-Url: http://git.kernel.org/git/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff;h=40359ccb836866435b03a0cb57345002b587d875

> --- a/block/blktrace.c
> +++ b/block/blktrace.c
..
> @@ -79,6 +79,8 @@ static u32 bio_act[3] __read_mostly = { 
>  	(((rw) & (1 << BIO_RW_BARRIER)) >> (BIO_RW_BARRIER - 0))
>  #define trace_sync_bit(rw)	\
>  	(((rw) & (1 << BIO_RW_SYNC)) >> (BIO_RW_SYNC - 1))
> +#define trace_ahead_bit(rw)	\
> +	(((rw) & (1 << BIO_RW_AHEAD)) << (BIO_RW_AHEAD - 0))
>  
>  /*
>   * The worker for the various blk_add_trace*() types. Fills out a


Than doesn't make sense, we are using the bit position in the BIO_RW_
name space twice instead of factoring it out like the other uses.

Looking at  include/linux/bio.h line 147 we find
#define BIO_RW_AHEAD    1

So this is moving it from bit 1 (value 2) to bit 2 (value 4).

I think the shift should be << (2 - BIO_RW_AHEAD).

milton
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