Re: [PATCH 4/6] perf_counter: Add PERF_COUNTER_IOC_SET_FILTER ioctl
From: Peter Zijlstra
Date: Tue Sep 08 2009 - 04:38:17 EST
On Tue, 2009年09月08日 at 08:49 +0800, Li Zefan wrote:
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Peter Zijlstra wrote:
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> On Mon, 2009年09月07日 at 18:48 +0200, Ingo Molnar wrote:
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>> * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
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>>
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>>> On Mon, 2009年09月07日 at 16:13 +0800, Li Zefan wrote:
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>>>> Allow to set profile filter via ioctl.
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>>> Hrm,.. not at all sure about this.. what are the ABI implications?
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>> I think the ABI should be fine if it's always a sub-set of C syntax.
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>> That would be C expressions initially. Hm?
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>
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> Right, so I've no clue what filter expressions look like, and the
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> changelog doesn't help us at all. It doesn't mention its a well
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> considered decision to henceforth freeze the expression syntax.
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>
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> Of course, since filters so far only work with tracepoint things, and
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> since you can only come by tracepoint things through debugfs, and since
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> anything debugfs is basically a free-for-all ABI-less world, we might be
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> good, but then this is a very ill-defined ioctl() indeed.
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>
>
> So please, consider this well -- there might not be a second chance.
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>
>
>
Ok, the expressions are:
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>
1. S = opr1 op opr2 (op: ==, !=, <, <=, >, >=.
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opr1 should be a field in the format file)
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2. E = S1 op S2 (op: ||, &&)
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3. E = E1 op E2 (op: ||, &&)
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4. () can be used
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>
I don't the syntax will be changed, but we may extend it, like
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adding not ! operator. Like, for a func ptr, besides "func==0xccee4400",
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we may want to allow "func==foo". Those extentions are ok for the
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ABI, right?
Sure, but my point is that you need to be aware that you're creating an
ABI and the changelog was virtually non-existent which didn't inspire
much confidence.
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