linux-kernel - ftrace: trace_pipe_raw, blocking, and splice()

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Message-ID: <CAA9TWobmZyyhPkumX5zN_Lp3J+XQA39R10bn9r0+Vt-mznD7og@mail.gmail.com>
Date:	Tue, 12 Jul 2011 17:27:33 -0700
From:	Slava Pestov <slavapestov@...gle.com>
To:	linux-kernel@...r.kernel.org
Cc:	Michael Rubin <mrubin@...gle.com>,
	David Sharp <dhsharp@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
Subject: ftrace: trace_pipe_raw, blocking, and splice()

Hi ftrace users,

I notice that tracing_buffers_splice_read() has this comment in it
around line 3900:

/* TODO: block */

Was the original intention that reading from trace_pipe_raw with
tracing enabled should block if there is no data available, rather
than returning with end of file?

If so, I suggest adding a new trace_raw special file which behaves
like the current trace_pipe_raw (return 0 on EOF). Then we'd change
trace_pipe_raw to block on EOF.

Does this sound reasonable or is breaking APIs like this unacceptable?

Slava
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