Re: [PATCH v6 2/5] fs: Convert kiocb rw_hint from enum to u16

[Adam Manzanares <Adam.Manzanares@wdc.com>]

On 5/22/18 8:32 AM, Jens Axboe wrote:
> On 5/22/18 9:07 AM, adam.manzanares@wdc.com wrote:
>> From: Adam Manzanares <adam.manzanares@wdc.com>
>>
>> In order to avoid kiocb bloat for per command iopriority support, rw_hint
>> is converted from enum to a u16. Added a guard around ki_hint assignment.
>>
>> Signed-off-by: Adam Manzanares <adam.manzanares@wdc.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> ---
>>   include/linux/fs.h | 13 +++++++++++--
>>   1 file changed, 11 insertions(+), 2 deletions(-)
>>
>> diff --git a/include/linux/fs.h b/include/linux/fs.h
>> index 7f07977bdfd7..50de40dbbb85 100644
>> --- a/include/linux/fs.h
>> +++ b/include/linux/fs.h
>> @@ -284,6 +284,8 @@ enum rw_hint {
>>   	WRITE_LIFE_EXTREME	= RWH_WRITE_LIFE_EXTREME,
>>   };
>>   
>> +#define MAX_KI_HINT		((1 << 16) - 1) /* ki_hint type is u16 */
> 
> Instead of having to do this and now rely on those now being synced,
> how about something like the below.
> 
> diff --git a/include/linux/fs.h b/include/linux/fs.h
> index 760d8da1b6c7..070438d0b62d 100644
> --- a/include/linux/fs.h
> +++ b/include/linux/fs.h
> @@ -299,7 +299,7 @@ struct kiocb {
>   	void (*ki_complete)(struct kiocb *iocb, long ret, long ret2);
>   	void			*private;
>   	int			ki_flags;
> -	enum rw_hint		ki_hint;
> +	u16			ki_hint;
>   } __randomize_layout;
>   
>   static inline bool is_sync_kiocb(struct kiocb *kiocb)
> @@ -1927,12 +1927,22 @@ static inline enum rw_hint file_write_hint(struct file *file)
>   
>   static inline int iocb_flags(struct file *file);
>   
> +static inline u16 ki_hint_validate(enum rw_hint hint)
> +{
> +	typeof(((struct kiocb *)0)->ki_hint) max_hint = -1;
> +
> +	if (hint <= max_hint)
> +		return hint;
> +
> +	return 0;
> +}
> +
>   static inline void init_sync_kiocb(struct kiocb *kiocb, struct file *filp)
>   {
>   	*kiocb = (struct kiocb) {
>   		.ki_filp = filp,
>   		.ki_flags = iocb_flags(filp),
> -		.ki_hint = file_write_hint(filp),
> +		.ki_hint = ki_hint_validate(file_write_hint(filp)),
>   	};
>   }

Looks good. I'll resubmit.

>   
>