linux-kernel - Re: [PATCH 1/1] tracing: Support reading trace event format file larger than PAGE

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Message-ID: <20250106171150.4d3da6e5@gandalf.local.home>
Date: Mon, 6 Jan 2025 17:11:50 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Shiju Jose <shiju.jose@...wei.com>
Cc: "mhiramat@...nel.org" <mhiramat@...nel.org>,
 "mathieu.desnoyers@...icios.com" <mathieu.desnoyers@...icios.com>,
 "linux-trace-kernel@...r.kernel.org" <linux-trace-kernel@...r.kernel.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, Linuxarm
 <linuxarm@...wei.com>, Jonathan Cameron <jonathan.cameron@...wei.com>,
 tanxiaofei <tanxiaofei@...wei.com>, "Zengtao (B)"
 <prime.zeng@...ilicon.com>
Subject: Re: [PATCH 1/1] tracing: Support reading trace event format file
 larger than PAGE_SIZE

On Mon, 6 Jan 2025 18:15:36 +0000
Shiju Jose <shiju.jose@...wei.com> wrote:

> >You see, it requires multiple reads to pull in an entire kernel pseudo file. None of
> >those reads are greater than PAGE_SIZE. Why should trace format files be any
> >different?  
> Thanks for the reply.
> Yes. I had a fix/workaround in the userspace rasdaemon with multiple reads like above
> as reported previously in the  following thread.  
> https://lore.kernel.org/lkml/3c9808a694d242cab35bab67602edebf@huawei.com/
> However thought a solution in the common kernel code for the format file
> may be better.  I will go ahead with the user space solution.

That would make it different than every other pseudo file in the kernel. I
rather not do that.

>  
> Also shared an information in the above thread about libtraceevent  __parse_event() does not
> return error when parse_format() fail with incomplete formt data, which resulted initialization for the
> trace event does not fail in the user space tool.

Hmm, can you send me the the format file that failed?

Just the output of "cat /sys/kernel/tracing/events/<system>/<event>/format"
will do.

-- Steve