Re: [PATCH bpf-next v2 1/3] bpf: add bpf_ksock_sendto() kfunc

["Kumar Kartikeya Dwivedi" <memxor@gmail.com>]

On Wed Oct 21, 2026 at 8:57 PM CEST, Andrii Nakryiko wrote:
> On Wed, Oct 21, 2026 at 11:39 AM Mahe Tardy <mahe.tardy@gmail.com> wrote:
>>
>> On Wed, Oct 21, 2026 at 10:56:23AM -0700, Andrii Nakryiko wrote:
>> > On Tue, Oct 20, 2026 at 8:59 AM Mahe Tardy <mahe.tardy@gmail.com> wrote:
>> > >
>> > > The motivation is to plumb more of the socket API into ksock, thus
>> > > supporting sendto() in addition to send() which makes a lot of sense in
>> > > the context of UDP sockets which are the only type currently supported.
>> > > This is useful when ksock is used to reply to specific addresses or send
>> > > to multiple addresses.
>> > >
>> > > Signed-off-by: Mahe Tardy <mahe.tardy@gmail.com>
>> > > ---
>> > >  net/core/bpf_ksock.c | 96 +++++++++++++++++++++++++++++++-------------
>> > >  1 file changed, 69 insertions(+), 27 deletions(-)
>> > >
>>
>> [...]
>>
>> > >
>> > > -       return ret;
>> > > +/**
>> > > + * bpf_ksock_sendto() - Send data through a BPF kernel socket to a remote address.
>> > > + * @ks:                The BPF kernel socket context. Must be an acquired reference.
>> > > + * @data:      Pointer to the data to send.
>> > > + * @data__sz:  Size of the data to send.
>> > > + * @addr__nullable: Pointer to an IPv4 or IPv6 socket address, or NULL to use
>> > > + *                the connected destination.
>> > > + * @addr__sz:  Size of the address union, ignored when the address is NULL.
>> > > + *
>> > > + * Sends data to the specified address, or to the connected destination when
>> > > + * the address is NULL, best-effort and nonblocking. This may sleep
>> > > + * (kernel_sendmsg), so it can only be called from sleepable BPF programs.
>> > > + *
>> > > + * Return: Number of bytes sent on success, negative errno on error.
>> > > + */
>> > > +__bpf_kfunc int bpf_ksock_sendto(struct bpf_ksock *ks, const void *data, u32 data__sz,
>> >
>> > This would limit API to fixed-sized data only. Have you considered
>> > passing dynptr as a source of data, so you can send a wider variety of
>> > data? I don't have a strong opinion whether we should add a separate
>> > API or convert this one into dynptr, but I do think that having
>> > ability to work with variable-sized data is super useful and should be
>> > added early on.
>>
>> Oh wow this is really cool that you send this now. I was working this
>> afternoon on trying to see if a ksock sendmsg() would make sense, but
>> with these static buffer limitations as arguments, it actually didn't.
>> I'm not familiar with dynptr so I didn't think about it, but after a
>> quick check it looks like it would be a good match with the ksock API!
>>
>> As I understand, since bpf_ksock_send() is already part of 7.3, it's
>> best to not touch it, and having a simple send() available with a
>> fixed-size data might make sense.
>
> agreed
>
>>
>> But since bpf_ksock_sendto() was just merged, we could make it evolve to
>> use dynptr perhaps? How much time do we have for something which was
>> merged yesterday to be part of a release? Is it going to be send with
>> the 7.4 pull soon?
>>
>
> I'd send a follow up in the next few days, it can go in as a fix for
> kfunc in rc1 or something, unless others have differing opinions on
> this
>

Another option is to add dynptr variants of both, a pattern we have in other
APIs as well, so there would be no rush. We just have two more kfuncs:
bpf_ksock_send_dynptr() and bpf_ksock_sendto_dynptr().

>> >
>> > > +                                const union bpf_ksock_addr *addr__nullable,
>> > > +                                u32 addr__sz)
>> > > +{
>> > > +       return ksock_sendto(ks, data, data__sz, addr__nullable, addr__sz);
>> > >  }
>> > >
>> > >  __bpf_kfunc_end_defs();
>> > > @@ -255,6 +296,7 @@ BTF_KFUNCS_START(ksock_kfunc_btf_ids)
>> > >  BTF_ID_FLAGS(func, bpf_ksock_release, KF_RELEASE)
>> > >  BTF_ID_FLAGS(func, bpf_ksock_acquire, KF_ACQUIRE | KF_RCU | KF_RET_NULL)
>> > >  BTF_ID_FLAGS(func, bpf_ksock_send, KF_SLEEPABLE)
>> > > +BTF_ID_FLAGS(func, bpf_ksock_sendto, KF_SLEEPABLE)
>> > >  BTF_KFUNCS_END(ksock_kfunc_btf_ids)
>> > >
>> > >  #ifdef CONFIG_BPF_LSM
>> > > --
>> > > 2.43.0
>> > >