linux-kernel - Re: [RFC PATCH 1/7] perf tools: Add API to config maps in bpf object

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Date:	Fri, 20 Nov 2015 16:13:21 +0800
From:	"Wangnan (F)" <wangnan0@...wei.com>
To:	<acme@...nel.org>, <ast@...mgrid.com>, <brendan.d.gregg@...il.com>
CC:	<a.p.zijlstra@...llo.nl>, <daniel@...earbox.net>,
	<dsahern@...il.com>, <hekuang@...wei.com>, <jolsa@...nel.org>,
	<lizefan@...wei.com>, <masami.hiramatsu.pt@...achi.com>,
	<namhyung@...nel.org>, <paulus@...ba.org>,
	<linux-kernel@...r.kernel.org>, <pi3orama@....com>,
	<xiakaixu@...wei.com>, Arnaldo Carvalho de Melo <acme@...hat.com>
Subject: Re: [RFC PATCH 1/7] perf tools: Add API to config maps in bpf object

On 2015/10/17 18:48, Wang Nan wrote:
> bpf__config_obj() is introduced as a core API to config BPF object
> after loading. One configuration option of maps is introduced. After
> this patch BPF object can accept configuration like:
>
>   maps.my_map.value=1234

There's an inconvience in this syntax.

In following cmdline:

  # perf record -e mybpf.c/maps.channel.value=1234/ ls

because of the greedy manner of flex, mybpf.c/maps.c would
be expressed as path of a BPF source file (and yes, it is a valid
path).

If flex has a non-greedy mode then it would be fixed easily. However,
the official flex docs reveals its policy that it doesn't and would not
provide non-greedy matching. Even if we have non-greedy matching,
we are unable to prohibit user to put their BPF object into path
like

/home/user/mybpf.c/thefile.c

Fortunately this patch has not beed merged, so we have a chance to fix
it at very beginning. I will replace all '.' in object config string
to ':', so the above cmdline becomes:

  # perf record -e mybpf.c/maps:channel:value=1234/ ls

[1] 
http://flex.sourceforge.net/manual/Why-doesn_0027t-flex-have-non_002dgreedy-operators-like-perl-does_003f.html

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