linux-kernel - Re: [PATCH blktrace v2 03/22] blktrace: add definitions for BLKTRACESETUP2

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Message-ID: <fb62594c-d881-4f06-9cf0-ca44968e5d3b@kernel.org>
Date: Wed, 1 Oct 2025 16:48:10 +0900
From: Damien Le Moal <dlemoal@...nel.org>
To: Johannes Thumshirn <johannes.thumshirn@....com>,
 Jens Axboe <axboe@...nel.dk>
Cc: Steven Rostedt <rostedt@...dmis.org>,
 Masami Hiramatsu <mhiramat@...nel.org>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-btrace@...r.kernel.org,
 John Garry <john.g.garry@...cle.com>, Hannes Reinecke <hare@...e.de>,
 Christoph Hellwig <hch@....de>, Naohiro Aota <naohiro.aota@....com>,
 Shinichiro Kawasaki <shinichiro.kawasaki@....com>,
 Chaitanya Kulkarni <chaitanyak@...dia.com>,
 "Martin K . Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH blktrace v2 03/22] blktrace: add definitions for
 BLKTRACESETUP2

On 9/26/25 00:04, Johannes Thumshirn wrote:
> Add definitions for a new BLKTRACESETUP2 ioctl(2).
> 
> This new ioctl(2) will request a new, updated structure layout from the
> kernel which enhances the storage size of the 'action' field in order to
> store additional tracepoints.
> 
> Signed-off-by: Johannes Thumshirn <johannes.thumshirn@....com>
> ---
>  blktrace_api.h | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/blktrace_api.h b/blktrace_api.h
> index 172b4c2..9f435a5 100644
> --- a/blktrace_api.h
> +++ b/blktrace_api.h
> @@ -139,9 +139,24 @@ struct blk_user_trace_setup {
>  	__u32 pid;
>  };
>  
> +/*
> + * User setup structure passed with BLKTRACESETUP2
> + */
> +struct blk_user_trace_setup2 {
> +	char name[32];			/* output */
> +	__u64 act_mask;			/* input */
> +	__u32 buf_size;			/* input */
> +	__u32 buf_nr;			/* input */
> +	__u64 start_lba;
> +	__u64 end_lba;
> +	__u32 pid;
> +	__u32 reserved;			/* for futute use */
> +};

Kernel side defined:

+struct blk_user_trace_setup2 {
+	char name[32];		/* output */
+	__u64 act_mask;		/* input */
+	__u32 buf_size;		/* input */
+	__u32 buf_nr;		/* input */
+	__u64 start_lba;
+	__u64 end_lba;
+	__u32 pid;
+	__u32 flags;		/* currently unused */
+	__u64 reserved[7];
+};

So not the same struct fields and size...

Why not use the definition in include/uapi/linux/blktrace_api.h ?

> +
>  #define BLKTRACESETUP _IOWR(0x12,115,struct blk_user_trace_setup)
>  #define BLKTRACESTART _IO(0x12,116)
>  #define BLKTRACESTOP _IO(0x12,117)
>  #define BLKTRACETEARDOWN _IO(0x12,118)
> +#define BLKTRACESETUP2 _IOWR(0x12, 142, struct blk_user_trace_setup2)

Same here. This is in include/uapi/linux/fs.h, so why duplicate it ?

>  
>  #endif

-- 
Damien Le Moal
Western Digital Research