netdev - Re: [PATCH bpf-next] flow_dissector: fix build failure without CONFIG

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Date:   Tue, 18 Sep 2018 14:33:49 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        netdev@...r.kernel.org
Cc:     ast@...nel.org, daniel@...earbox.net,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH bpf-next] flow_dissector: fix build failure without
 CONFIG_NET

On 9/18/18 1:20 PM, Willem de Bruijn wrote:
> From: Willem de Bruijn <willemb@...gle.com>
> 
> If boolean CONFIG_BPF_SYSCALL is enabled, kernel/bpf/syscall.c will
> call flow_dissector functions from net/core/flow_dissector.c.
> 
> This causes this build failure if CONFIG_NET is disabled:
> 
>     kernel/bpf/syscall.o: In function `__x64_sys_bpf':
>     syscall.c:(.text+0x3278): undefined reference to
>     `skb_flow_dissector_bpf_prog_attach'
>     syscall.c:(.text+0x3310): undefined reference to
>     `skb_flow_dissector_bpf_prog_detach'
>     kernel/bpf/syscall.o:(.rodata+0x3f0): undefined reference to
>     `flow_dissector_prog_ops'
>     kernel/bpf/verifier.o:(.rodata+0x250): undefined reference to
>     `flow_dissector_verifier_ops'
> 
> Analogous to other optional BPF program types in syscall.c, add stubs
> if the relevant functions are not compiled and move the BPF_PROG_TYPE
> definition in the #ifdef CONFIG_NET block.
> 
> Fixes: d58e468b1112 ("flow_dissector: implements flow dissector BPF hook")
> Reported-by: Randy Dunlap <rdunlap@...radead.org>
> Signed-off-by: Willem de Bruijn <willemb@...gle.com>

Works for me.  Thanks.

Acked-by: Randy Dunlap <rdunlap@...radead.org> # build-tested


> ---
>  include/linux/bpf_types.h |  2 +-
>  include/linux/skbuff.h    | 13 +++++++++++++
>  2 files changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/bpf_types.h b/include/linux/bpf_types.h
> index 22083712dd18..c9bd6fb765b0 100644
> --- a/include/linux/bpf_types.h
> +++ b/include/linux/bpf_types.h
> @@ -16,6 +16,7 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_LWT_SEG6LOCAL, lwt_seg6local)
>  BPF_PROG_TYPE(BPF_PROG_TYPE_SOCK_OPS, sock_ops)
>  BPF_PROG_TYPE(BPF_PROG_TYPE_SK_SKB, sk_skb)
>  BPF_PROG_TYPE(BPF_PROG_TYPE_SK_MSG, sk_msg)
> +BPF_PROG_TYPE(BPF_PROG_TYPE_FLOW_DISSECTOR, flow_dissector)
>  #endif
>  #ifdef CONFIG_BPF_EVENTS
>  BPF_PROG_TYPE(BPF_PROG_TYPE_KPROBE, kprobe)
> @@ -32,7 +33,6 @@ BPF_PROG_TYPE(BPF_PROG_TYPE_LIRC_MODE2, lirc_mode2)
>  #ifdef CONFIG_INET
>  BPF_PROG_TYPE(BPF_PROG_TYPE_SK_REUSEPORT, sk_reuseport)
>  #endif
> -BPF_PROG_TYPE(BPF_PROG_TYPE_FLOW_DISSECTOR, flow_dissector)
>  
>  BPF_MAP_TYPE(BPF_MAP_TYPE_ARRAY, array_map_ops)
>  BPF_MAP_TYPE(BPF_MAP_TYPE_PERCPU_ARRAY, percpu_array_map_ops)
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index ce0e863f02a2..76be85ea392a 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1194,10 +1194,23 @@ void skb_flow_dissector_init(struct flow_dissector *flow_dissector,
>  			     const struct flow_dissector_key *key,
>  			     unsigned int key_count);
>  
> +#ifdef CONFIG_NET
>  int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
>  				       struct bpf_prog *prog);
>  
>  int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr);
> +#else
> +static inline int skb_flow_dissector_bpf_prog_attach(const union bpf_attr *attr,
> +						     struct bpf_prog *prog)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static inline int skb_flow_dissector_bpf_prog_detach(const union bpf_attr *attr)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#endif
>  
>  bool __skb_flow_dissect(const struct sk_buff *skb,
>  			struct flow_dissector *flow_dissector,
> 


-- 
~Randy