From: Daniel Borkmann <daniel@iogearbox•net>
To: Daniel Mack <daniel@zonque•org>, htejun@fb•com, ast@fb•com
Cc: davem@davemloft•net, kafai@fb•com, fw@strlen•de,
pablo@netfilter•org, harald@redhat•com, netdev@vger•kernel.org,
sargun@sargun•me
Subject: Re: [PATCH v3 3/6] bpf: add BPF_PROG_ATTACH and BPF_PROG_DETACH commands
Date: Mon, 05 Sep 2016 19:09:27 +0200 [thread overview]
Message-ID: <57CDA6C7.5060501@iogearbox.net> (raw)
In-Reply-To: <7f69d0ee-df6e-0d30-7198-16a978e53068@zonque.org>
On 09/05/2016 04:09 PM, Daniel Mack wrote:
> On 09/05/2016 03:56 PM, Daniel Borkmann wrote:
>> On 09/05/2016 02:54 PM, Daniel Mack wrote:
>>> On 08/30/2016 01:00 AM, Daniel Borkmann wrote:
>>>> On 08/26/2016 09:58 PM, Daniel Mack wrote:
>>>
>>>>> enum bpf_map_type {
>>>>> @@ -147,6 +149,13 @@ union bpf_attr {
>>>>> __aligned_u64 pathname;
>>>>> __u32 bpf_fd;
>>>>> };
>>>>> +
>>>>> + struct { /* anonymous struct used by BPF_PROG_ATTACH/DETACH commands */
>>>>> + __u32 target_fd; /* container object to attach to */
>>>>> + __u32 attach_bpf_fd; /* eBPF program to attach */
>>>>> + __u32 attach_type; /* BPF_ATTACH_TYPE_* */
>>>>> + __u64 attach_flags;
>>>>
>>>> Could we just do ...
>>>>
>>>> __u32 dst_fd;
>>>> __u32 src_fd;
>>>> __u32 attach_type;
>>>>
>>>> ... and leave flags out, since unused anyway? Also see below.
>>>
>>> I'd really like to keep the flags, even if they're unused right now.
>>> This only adds 8 bytes during the syscall operation, so it doesn't harm.
>>> However, we cannot change the userspace API after the fact, and who
>>> knows what this (rather generic) interface will be used for later on.
>>
>> With the below suggestion added, then flags doesn't need to be
>> added currently as it can be done safely at a later point in time
>> with respecting old binaries. See also the syscall handling code
>> in kernel/bpf/syscall.c +825 and the CHECK_ATTR() macro. The
>> underlying idea of this was taken from perf_event_open() syscall
>> back then, see [1] for a summary.
>>
>> [1] https://lkml.org/lkml/2014/8/26/116
>
> Yes, I know that's possible, and I like the idea, but I don't think any
> new interface should come without flags really, as flags are something
> that will most certainly be needed at some point anyway. I didn't have
> them in my first shot, but Alexei pointed out that they should be added,
> and I agree.
>
> Also, this optimization wouldn't make the transported struct payload any
> smaller anyway, because the member of that union used by BPF_PROG_LOAD
> is still by far the biggest.
>
> I really don't think it's worth sparing 8 bytes here and then do the
> binary compat dance after flags are added, for no real gain.
Sure, but there's not much of a dance needed, see for example how map_flags
were added some time ago. So, iff there's really no foreseeable use-case in
sight and since we have this flexibility in place already, then I don't quite
follow why it's needed, if there's zero pain to add it later on. I would
understand it of course, if it cannot be handled later on anymore.
next prev parent reply other threads:[~2016-09-05 17:09 UTC|newest]
Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-08-26 19:58 [PATCH v3 0/6] Add eBPF hooks for cgroups Daniel Mack
2016-08-26 19:58 ` [PATCH v3 1/6] bpf: add new prog type for cgroup socket filtering Daniel Mack
2016-08-29 22:14 ` Daniel Borkmann
2016-09-05 12:48 ` Daniel Mack
2016-08-26 19:58 ` [PATCH v3 2/6] cgroup: add support for eBPF programs Daniel Mack
2016-08-27 0:03 ` Alexei Starovoitov
2016-09-05 12:47 ` Daniel Mack
2016-08-29 22:42 ` Daniel Borkmann
2016-09-05 12:50 ` Daniel Mack
2016-08-29 23:04 ` Sargun Dhillon
2016-09-05 14:49 ` Daniel Mack
2016-09-05 21:40 ` Sargun Dhillon
2016-09-05 22:39 ` Alexei Starovoitov
2016-08-26 19:58 ` [PATCH v3 3/6] bpf: add BPF_PROG_ATTACH and BPF_PROG_DETACH commands Daniel Mack
2016-08-27 0:08 ` Alexei Starovoitov
2016-09-05 12:56 ` Daniel Mack
2016-09-05 15:30 ` David Laight
2016-09-05 15:40 ` Daniel Mack
2016-09-05 17:29 ` Joe Perches
2016-08-29 23:00 ` Daniel Borkmann
2016-09-05 12:54 ` Daniel Mack
2016-09-05 13:56 ` Daniel Borkmann
2016-09-05 14:09 ` Daniel Mack
2016-09-05 17:09 ` Daniel Borkmann [this message]
2016-09-05 18:32 ` Alexei Starovoitov
2016-09-05 18:43 ` Daniel Mack
2016-08-26 19:58 ` [PATCH v3 4/6] net: filter: run cgroup eBPF ingress programs Daniel Mack
2016-08-29 23:15 ` Daniel Borkmann
2016-08-26 19:58 ` [PATCH v3 5/6] net: core: run cgroup eBPF egress programs Daniel Mack
2016-08-29 22:03 ` Daniel Borkmann
2016-08-29 22:23 ` Sargun Dhillon
2016-09-05 14:22 ` Daniel Mack
2016-09-06 17:14 ` Daniel Borkmann
2016-08-26 19:58 ` [PATCH v3 6/6] samples: bpf: add userspace example for attaching eBPF programs to cgroups Daniel Mack
2016-08-27 13:00 ` [PATCH v3 0/6] Add eBPF hooks for cgroups Rami Rosen
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