netdev - Re: [PATCH v7 tip 3/8] tracing: allow BPF programs to call bpf_ktime_get

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Message-ID: <550AED5D.3010700@plumgrid.com>
Date:	Thu, 19 Mar 2015 08:38:05 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Steven Rostedt <rostedt@...dmis.org>
CC:	Ingo Molnar <mingo@...nel.org>, Namhyung Kim <namhyung@...nel.org>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	Jiri Olsa <jolsa@...hat.com>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"David S. Miller" <davem@...emloft.net>,
	Daniel Borkmann <daniel@...earbox.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 tip 3/8] tracing: allow BPF programs to call bpf_ktime_get_ns()

On 3/19/15 8:11 AM, Steven Rostedt wrote:
> On Mon, 16 Mar 2015 14:49:39 -0700
> Alexei Starovoitov <ast@...mgrid.com> wrote:
>
>> bpf_ktime_get_ns() is used by programs to compue time delta between events
>
>   "compute"

ok :)

>> +	[BPF_FUNC_ktime_get_ns] = {
>> +		.func = bpf_ktime_get_ns,
>> +		.gpl_only = true,
>> +		.ret_type = RET_INTEGER,
>
> Hmm, a nanosecond value returned as integer? Is there a way to make
> this a 64 bit return type, or is RET_INTEGER default to 64 bits in BPF
> functions?

RET_INTEGER doesn't mean C 'int' width. It means non-pointer and
non-void value. The return value is always promoted to full
register width which is 64-bit.


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