linux-kernel - Re: [PATCH] bpf/stackmap: Implement bpf_get_next

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Date:   Wed, 24 Jan 2018 20:53:56 -0800
From:   Joel Fernandes <joelaf@...gle.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Brendan Gregg <bgregg@...flix.com>
Subject: Re: [PATCH] bpf/stackmap: Implement bpf_get_next_key

On Wed, Jan 24, 2018 at 8:42 PM, Alexei Starovoitov
<alexei.starovoitov@...il.com> wrote:
> On Wed, Jan 24, 2018 at 08:37:52PM -0800, Joel Fernandes wrote:
>> Currently stackmaps can't be iterated over. The keys are obtained
>> through other maps and look ups have to be performed. In new usecases,
>> its useful to be able to iterate over the stackmap independently.
>> Implement bpf_get_next_key to make this possible.
>>
>> More details of use case:
>> Currently iterating over stack maps is done like so, for example
>> in BCC tools offcputime script:
>> 1. Obtain keys from the 'counts' hash map.
>> 2. Look up stackmap with each of the keys obtained from step 1.
>>
>> This makes the iteration of stackmap dependent on the counts map.
>> In a new tool I'm working on called BPFd [1], it gives a huge speed
>> up when I dump entire maps before transmitting them to BCC tools
>> on a different machine [2]. This patch makes it possible to dump
>> stackmaps independent of other maps.
>>
>> Tested on x86 and arm64 machines.
>>
>> [1] https://lwn.net/Articles/744522/
>> [2] https://github.com/joelagnel/bpfd/issues/8
>>
>> Cc: Alexei Starovoitov <ast@...nel.org>
>> Cc: Daniel Borkmann <daniel@...earbox.net>
>> Cc: Brendan Gregg <bgregg@...flix.com>
>> Cc: Brenden Blanco <bblanco@...il.com>
>> Signed-off-by: Joel Fernandes <joelaf@...gle.com>
>> ---
>>  kernel/bpf/stackmap.c | 18 +++++++++++++++++-
>>  1 file changed, 17 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/bpf/stackmap.c b/kernel/bpf/stackmap.c
>> index a15bc636cc98..b0bf7d009f76 100644
>> --- a/kernel/bpf/stackmap.c
>> +++ b/kernel/bpf/stackmap.c
>> @@ -228,7 +228,23 @@ int bpf_stackmap_copy(struct bpf_map *map, void *key, void *value)
>>
>>  static int stack_map_get_next_key(struct bpf_map *map, void *key, void *next_key)
>>  {
>> -     return -EINVAL;
>> +     struct bpf_stack_map *smap = container_of(map, struct bpf_stack_map, map);
>> +     u32 id = 0;
>
> did you check net-next tree before sending the patch?

Oh. I was a bit late to send it! Glad its done though.

> Also please see Documentation/bpf/bpf_devel_QA.txt

Sure, if you don't mind could you elaborate what I screwed up from the
QA with regard to this patch? Sorry if I missed something.

thanks,

- Joel