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

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Message-ID: <CAFR8ueeG+aciSpR9HXTgw75mNWW-H3HN02Xhh5OonQn0gGQ5Fg@mail.gmail.com>
Date:	Thu, 1 Mar 2012 18:27:14 -0500
From:	Muthu Kumar <muthu.lkml@...il.com>
To:	Jens Axboe <axboe@...nel.dk>
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 Thu, Mar 1, 2012 at 5:03 PM, Jens Axboe <axboe@...nel.dk> wrote:
> 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.

Yes, its a big patch - attached. grepped and verified all cases are
taken care of and compiles in my setup.

Regards,
Muthu

View attachment "change-bio-flags-defines.patch" of type "text/x-patch" (47423 bytes)