linux-kernel - Re: [PATCH] Fix setting bio flags in drivers (sd

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Message-ID: <4F4FF23C.8080201@kernel.dk>
Date:	Thu, 01 Mar 2012 23:03:40 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Muthu Kumar <muthu.lkml@...il.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, torvalds@...ux-foundation.org,
	martin.petersen@...cle.com
Subject: Re: [PATCH] Fix setting bio flags in drivers (sd_dif/floppy).

On 03/01/2012 10:20 PM, Muthu Kumar wrote:
> On Thu, Mar 1, 2012 at 12:25 PM, Jens Axboe <axboe@...nel.dk> wrote:
>> On 2012-03-01 21:23, Muthu Kumar wrote:
>>>>>                       kunmap_atomic(sdt, KM_USER0);
>>>>>               }
>>>>>
>>>>> -             bio->bi_flags |= BIO_MAPPED_INTEGRITY;
>>>>> +             bio->bi_flags |= (1 << BIO_MAPPED_INTEGRITY);
>>>>>       }
>>>>>
>>>>>       return 0;
>>>>
>>>> urgh.  This isn't the first time.
>>>>
>>>> It's too easy for people to make this mistake.  I'm not sure what a
>>>> good fix would be - I don't think sparse can save us with __bitwise or
>>>> similar.
>>>>
>>>> The approach we took in buffer_head.h with BH_Foo and BUFFER_FNS
>>>> accessors worked pretty well.
>>>>
>>>
>>> Does this look good? BTW, I used the non-atomic variants __set/__clear
>>> to match the behavior of current usage.
>>> If this looks good, I can send the proper patch as attachment (so no
>>> line wraps :)
>>
>> Lets not wrap this in macros, it just makes the code harder to read.
>> Making the BIO_ flags a bit shift value was a mistake in hindsight, too
>> easy to get wrong.
>>
>> If we're going to be changing everything anyway, it'd be better to have
>> __ variants if we really need the bit shifts, and the non __ variants be
>> the value. Similar to what is done for request flags.
>>
>> --
>> Jens Axboe
>>
> 
> 
> You mean, like this? (sparing the gmail line wrap)
> 
> diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> index 4053cbd..035e1ef 100644
> --- a/include/linux/blk_types.h
> +++ b/include/linux/blk_types.h
> @@ -83,19 +83,35 @@ struct bio {
>  /*
>   * bio flags
>   */
> -#define BIO_UPTODATE   0       /* ok after I/O completion */
> -#define BIO_RW_BLOCK   1       /* RW_AHEAD set, and read/write would block */
> -#define BIO_EOF                2       /* out-out-bounds error */
> -#define BIO_SEG_VALID  3       /* bi_phys_segments valid */
> -#define BIO_CLONED     4       /* doesn't own data */
> -#define BIO_BOUNCED    5       /* bio is a bounce bio */
> -#define BIO_USER_MAPPED 6      /* contains user pages */
> -#define BIO_EOPNOTSUPP 7       /* not supported */
> -#define BIO_NULL_MAPPED 8      /* contains invalid user pages */
> -#define BIO_FS_INTEGRITY 9     /* fs owns integrity data, not block layer */
> -#define BIO_QUIET      10      /* Make BIO Quiet */
> -#define BIO_MAPPED_INTEGRITY 11/* integrity metadata has been remapped */
> -#define bio_flagged(bio, flag) ((bio)->bi_flags & (1 << (flag)))
> +enum bio_flag_bits {
> +    __BIO_UPTODATE,             /* ok after I/O completion */
> +    __BIO_RW_BLOCK,             /* RW_AHEAD set, and read/write would block */
> +    __BIO_EOF,                  /* out-out-bounds error */
> +    __BIO_SEG_VALID,            /* bi_phys_segments valid */
> +    __BIO_CLONED,               /* doesn't own data */
> +    __BIO_BOUNCED,              /* bio is a bounce bio */
> +    __BIO_USER_MAPPED,          /* contains user pages */
> +    __BIO_EOPNOTSUPP,           /* not supported */
> +    __BIO_NULL_MAPPED,          /* contains invalid user pages */
> +    __BIO_FS_INTEGRITY,         /* fs owns integrity data, not block layer */
> +    __BIO_QUIET,                /* Make BIO Quiet */
> +    __BIO_MAPPED_INTEGRITY,     /* integrity metadata has been remapped */
> +};
> +
> +#define BIO_UPTODATE            (1 << __BIO_UPTODATE)
> +#define BIO_RW_BLOCK            (1 << __BIO_RW_BLOCK)
> +#define BIO_EOF                 (1 << __BIO_EOF)
> +#define BIO_SEG_VALID           (1 << __BIO_SEG_VALID)
> +#define BIO_CLONED              (1 << __BIO_CLONED)
> +#define BIO_BOUNCED             (1 << __BIO_BOUNCED)
> +#define BIO_USER_MAPPED         (1 << __BIO_USER_MAPPED)
> +#define BIO_EOPNOTSUPP          (1 << __BIO_EOPNOTSUPP)
> +#define BIO_NULL_MAPPED         (1 << __BIO_NULL_MAPPED)
> +#define BIO_FS_INTEGRITY        (1 << __BIO_FS_INTEGRITY)
> +#define BIO_QUIET               (1 << __BIO_QUIET)
> +#define BIO_MAPPED_INTEGRITY    (1 << __BIO_MAPPED_INTEGRITY)
> +
> +#define bio_flagged(bio, flag) ((bio)->bi_flags & (flag))
> 
>  /*
>   * top 4 bits of bio flags indicate the pool this bio came from

Yes, exactly. Only problem is that it would be a big patch, and old code
would still compile. We'd probably need to make all those a bit
different, ala

+#define BIO_F_UPTODATE         (1 << __BIO_UPTODATE)

to be completely safe and catch any use case.

-- 
Jens Axboe

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