linux-kernel - Re: [PATCH v6 2/5] fs: Convert kiocb rw

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Date:   Tue, 22 May 2018 09:32:26 -0600
From:   Jens Axboe <axboe@...nel.dk>
To:     adam.manzanares@....com, viro@...iv.linux.org.uk,
        linux-fsdevel@...r.kernel.org, bcrl@...ck.org
Cc:     tglx@...utronix.de, mingo@...nel.org, pombredanne@...b.com,
        kstewart@...uxfoundation.org, gregkh@...uxfoundation.org,
        bigeasy@...utronix.de, jack@...e.cz, darrick.wong@...cle.com,
        rgoldwyn@...e.com, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-aio@...ck.org,
        linux-api@...r.kernel.org, hch@...radread.org, jmoyer@...hat.com
Subject: Re: [PATCH v6 2/5] fs: Convert kiocb rw_hint from enum to u16

On 5/22/18 9:07 AM, adam.manzanares@....com wrote:
> From: Adam Manzanares <adam.manzanares@....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@....com>
> Reviewed-by: Christoph Hellwig <hch@....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)),
 	};
 }
 

-- 
Jens Axboe