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Subject: Re: [PATCH v3 3/7 UPDATE] perf tools: Add option for the path of
 buildid dsos under symfs
To: David Ahern <dsahern@gmail.com>, <peterz@infradead.org>,
        <mingo@redhat.com>, <acme@kernel.org>,
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        <penberg@kernel.org>
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From: Hekuang <hekuang@huawei.com>
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Date: Wed, 18 May 2016 10:48:48 +0800
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在 2016/5/18 9:51, David Ahern 写道:
> On 5/17/16 7:47 PM, Hekuang wrote:
>>
>>
>> 在 2016/5/16 10:50, David Ahern 写道:
>>> On 5/15/16 7:30 PM, Hekuang wrote:
>>>> In previous patch, I use 'perf buildid-cache -a' to add vdso
>>>> binary into the HOST buildid dir.
>>>
>>> So 'perf buildid-cache' needs the symfs option?
>>>
>>>
>> With this patch 'PATCH v3 3/7 UPDATE', the tree of symfs dir is
>> like this:
>>
>> ├── debug($(dso-prefix))
>> │   ├── .build-id
>> │   │   ├── 3a
>> │   │   │   └── e5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd ->
>> ../../[kernel.kallsyms]/3ae5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd
>> │   │   └── 84
>> │   │       └── dbd75729adba57cc42f5544b25de571c0c8731 ->
>> ../../[vdso32]/84dbd75729adba57cc42f5544b25de571c0c8731
>> │   ├── [kernel.kallsyms]
>> │   │   └── 3ae5ba6d4e532ad529e43ccf1ce1ddf8a64a4fdd
>> │   ├── [vdso]
>> │   │   └── 84dbd75729adba57cc42f5544b25de571c0c8731
>> │   └── [vdso32]
>> │       └── 84dbd75729adba57cc42f5544b25de571c0c8731
>> ├── lib
>> │   ├── ld-2.22.so
>> │   └── libc-2.22.so
>> ├── tmp
>> │   └── hello
>> └── xxx
>>
>> So all binaries we need are included in the symfs dir. I think
>> this is consistent with your idea explained in previous mails.
>>
>> With this symfs, we do not need buildid dir anymore and what's
>> your idea on 'perf buildid-cache' needs symfs option? after all,
>> that only effects on buildid dir.
>
> I don't understand why dso-prefix option is needed? Why make me type 
> yet more options to the analysis command? Why can't the directory be 
> located under the symfs tree in a known location and populated the 
> same way it is without symfs?
>
>
Because the default buidid folder path is $HOME/.debug/.buildid,
and this $HOME is on the target machine, not the same as $HOME
on the host. Without that option, we need to copy $HOME/.debug/.buildid
to the 'known location in symfs', that's also an extra work.