Message-ID: <558D0F5F.2000700@plumgrid.com>
Date: Fri, 26 Jun 2015 01:37:51 -0700
From: Alexei Starovoitov <ast@plumgrid.com>
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.10; rv:31.0) Gecko/20100101 Thunderbird/31.7.0
MIME-Version: 1.0
To: Wang Nan <wangnan0@huawei.com>, acme@kernel.org, brendan.d.gregg@gmail.com,
        daniel@iogearbox.net, namhyung@kernel.org,
        masami.hiramatsu.pt@hitachi.com, paulus@samba.org,
        a.p.zijlstra@chello.nl, mingo@redhat.com, jolsa@kernel.org,
        dsahern@gmail.com
CC: linux-kernel@vger.kernel.org, lizefan@huawei.com, hekuang@huawei.com,
        xiakaixu@huawei.com, pi3orama@163.com
Subject: Re: [RFC PATCH v8 00/49] perf tools: filtering events using eBPF
 programs
References: <1435149113-51142-1-git-send-email-wangnan0@huawei.com>
In-Reply-To: <1435149113-51142-1-git-send-email-wangnan0@huawei.com>
Content-Type: text/plain; charset=windows-1252; format=flowed
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 1407
Lines: 33

On 6/24/15 5:31 AM, Wang Nan wrote:
> The core stuffs in this series resides in 38/49 - 49/49, which allow
> users to access kernel data through parameters of eBPF programs. Now
> it is possible to write eBPF programs like this:
>
>   SEC("get_superblock=journal_get_superblock journal->j_errno")
>   int get_superblock(struct pt_regs *ctx, int err, int j_errno)
>   {
>           char fmt[] = "j_errno=%lx\n";
>           bpf_trace_printk(fmt, sizeof(fmt), j_errno);
> 	 if (j_errno)
>                   return 1;
> 	 return 0;
>   }
>
> Where, 'j_errno' in that function will be dereferenced according to
> dwarf information by prologue generated by perf. 'err' indicates the
> successfulness of the dereferencing.

Looks great. Very useful addition.

> In addition, this series of patches supports setting BPF program to
> multiple probing points and generate different prologue for all of them
> if necessary. Using glob matching is also allowed. In the above
> example, there will be two journal_get_superblock() functions in kernel
> if we compile both jbd and jbd2. That BPF function tracks both of them.

Sounds ok, but what is the real use case for it?
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/