Re: [PATCH] REQ-flags to/from BIO-flags bugfix

From: Boaz Harrosh <bharrosh@panasas.com>
To: Matthew Wilcox <matthew@wil.cx>
Cc: James Bottomley <James.Bottomley@HansenPartnership.com>,
	Jens Axboe <jens.axboe@oracle.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Gabriel C <nix.or.die@googlemail.com>,
	linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org,
	Hannes Reinecke <hare@suse.de>
Subject: Re: [PATCH] REQ-flags to/from BIO-flags bugfix
Date: Wed, 12 Dec 2007 18:06:45 +0200	[thread overview]
Message-ID: <47600715.9000303@panasas.com> (raw)
In-Reply-To: <20071212151813.GJ26334@parisc-linux.org>

On Wed, Dec 12 2007 at 17:18 +0200, Matthew Wilcox <matthew@wil.cx> wrote:
> On Wed, Dec 12, 2007 at 01:03:10PM +0200, Boaz Harrosh wrote:
>>  - BIO flags bio->bi_rw and REQ flags req->cmd_flags no longer match.
>>    Remove comments and do a proper translation between the 2 systems.
> 
> I'd rather see them resynchronised ... in a way that makes it obvious
> that they should be desynced again:
> 
> I don't know whether BIO_RW_BARRIER is __REQ_SOFTBARRIER or
> __REQ_HARDBARRIER, so I didn't include that in this patch.  There also
> doesn't seem to be a __REQ equivalent to BIO_RW_AHEAD, but we can do
> the other four bits (and leave gaps for those two).
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index d18ee67..6aef34b 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -167,11 +167,13 @@ enum {
>  };
>  
>  /*
> - * request type modified bits. first three bits match BIO_RW* bits, important
> + * request type modified bits.  Don't change without looking at bi_rw flags
>   */
>  enum rq_flag_bits {
> -	__REQ_RW,		/* not set, read. set, write */
> -	__REQ_FAILFAST,		/* no low level driver retries */
> +	__REQ_RW = BIO_RW,	/* not set, read. set, write */
> +	__REQ_FAILFAST = BIO_RW_FAILFAST, /* no low level driver retries */
> +	__REQ_RW_SYNC = BIO_RW_SYNC,	/* request is sync (O_DIRECT) */
> +	__REQ_RW_META = BIO_RW_META,	/* metadata io request */
>  	__REQ_SORTED,		/* elevator knows about this request */
>  	__REQ_SOFTBARRIER,	/* may not be passed by ioscheduler */
>  	__REQ_HARDBARRIER,	/* may not be passed by drive either */
> @@ -185,9 +187,7 @@ enum rq_flag_bits {
>  	__REQ_QUIET,		/* don't worry about errors */
>  	__REQ_PREEMPT,		/* set for "ide_preempt" requests */
>  	__REQ_ORDERED_COLOR,	/* is before or after barrier */
> -	__REQ_RW_SYNC,		/* request is sync (O_DIRECT) */
>  	__REQ_ALLOCED,		/* request came from our alloc pool */
> -	__REQ_RW_META,		/* metadata io request */
>  	__REQ_NR_BITS,		/* stops here */
>  };
>  
> 
Thats not enough You still need to fix code in ll_rw_blk(), I would
define a rq_flags_bio_match_mask = 0xf for that. 
(and also add what Jens called "needed" with the
BIO_RW_AHEAD selects REQ_FAILFAST.)

And I still don't understand why, for example, "Domain Validation" fails
with the original patch. What sets BIO_RW_FAILFAST and than panics
on Errors?
(All I see is this flag set in dm/multipath.c & dm-mpath.c)

Boaz