linux-kernel - Re: [PATCH 04/16] blktrace: add definitions for struct blk_io

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Message-ID: <20250919150847.GD28352@lst.de>
Date: Fri, 19 Sep 2025 17:08:47 +0200
From: Christoph Hellwig <hch@....de>
To: Johannes Thumshirn <johannes.thumshirn@....com>
Cc: Jens Axboe <axboe@...nel.dk>, 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>, Damien Le Moal <dlemoal@...nel.org>,
	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 04/16] blktrace: add definitions for struct
 blk_io_trace2

On Tue, Sep 09, 2025 at 01:05:59PM +0200, Johannes Thumshirn wrote:
> +struct blk_io_trace2 {
> +	__u32 magic;		/* MAGIC << 8 | BLK_IO_TRACE2_VERSION */
> +	__u32 sequence;		/* event number */
> +	__u64 time;		/* in nanoseconds */
> +	__u64 sector;		/* disk offset */
> +	__u32 bytes;		/* transfer length */
> +	__u32 pid;		/* who did it */
> +	__u64 action;		/* what happened */
> +	__u32 device;		/* device number */
> +	__u32 cpu;		/* on what cpu did it happen */
> +	__u16 error;		/* completion error */
> +	__u16 pdu_len;		/* length of data after this trace */
> +	/* cgroup id will be stored here if exists */
> +};

This structure is not u64-aligned, which means it will have different
sizes for x86-32 vs all other architectures, making it a pain to handle.

Also maybe add some extra padding so that we can extend this?