Re: [PATCH 2/7] udp: seq_file: Remove bpf_seq_afinfo from udp_iter_state

[Martin KaFai Lau <martin.lau@linux.dev>]

On 4/18/23 8:31 AM, Aditi Ghag wrote:
> This is a preparatory commit to remove the field. The field was
> previously shared between proc fs and BPF UDP socket iterators. As the
> follow-up commits will decouple the implementation for the iterators,
> remove the field. As for BPF socket iterator, filtering of sockets is
> exepected to be done in BPF programs.
> 
> Suggested-by: Martin KaFai Lau <martin.lau@kernel.org>
> Signed-off-by: Aditi Ghag <aditi.ghag@isovalent.com>
> ---
>   include/net/udp.h |  1 -
>   net/ipv4/udp.c    | 34 ++++------------------------------
>   2 files changed, 4 insertions(+), 31 deletions(-)
> 
> diff --git a/include/net/udp.h b/include/net/udp.h
> index de4b528522bb..5cad44318d71 100644
> --- a/include/net/udp.h
> +++ b/include/net/udp.h
> @@ -437,7 +437,6 @@ struct udp_seq_afinfo {
>   struct udp_iter_state {
>   	struct seq_net_private  p;
>   	int			bucket;
> -	struct udp_seq_afinfo	*bpf_seq_afinfo;
>   };
>   
>   void *udp_seq_start(struct seq_file *seq, loff_t *pos);
> diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
> index c605d171eb2d..3c9eeee28678 100644
> --- a/net/ipv4/udp.c
> +++ b/net/ipv4/udp.c
> @@ -2997,10 +2997,7 @@ static struct sock *udp_get_first(struct seq_file *seq, int start)
>   	struct udp_table *udptable;
>   	struct sock *sk;
>   
> -	if (state->bpf_seq_afinfo)
> -		afinfo = state->bpf_seq_afinfo;
> -	else
> -		afinfo = pde_data(file_inode(seq->file));
> +	afinfo = pde_data(file_inode(seq->file));

I can see how this change will work after patch 4. However, this patch alone 
cannot work independently as is. The udp bpf iter still uses the 
udp_get_{first,next} and udp_seq_stop() up-to this patch.

First, patch 3 refactoring should be done before patch 2 here. The removal of 
'struct udp_seq_afinfo *bpf_seq_afinfo' in patch 2 should be done when all the 
necessary refactoring is in-place first.

Also, this afinfo is passed to udp_get_table_afinfo(). How about renaming 
udp_get_table_afinfo() to udp_get_table_seq() and having it take the "seq" as 
the arg instead. This probably will deserve another refactoring patch before 
finally removing bpf_seq_afinfo. Something like this (un-compiled code):

static struct udp_table *udp_get_table_seq(struct seq_file *seq,
                                            struct net *net)
{
  	const struct udp_seq_afinfo *afinfo;

         if (st->bpf_seq_afinfo)
                 return net->ipv4.udp_table;

	afinfo = pde_data(file_inode(seq->file));
         return afinfo->udp_table ? : net->ipv4.udp_table;
}

Of course, when the later patch finally removes the bpf_seq_afinfo, the 'if 
(st->bpf_seq_afinfo)' test should be replaced with the 'if (seq->op == 
&bpf_iter_udp_seq_ops)' test.

That will also make the afinfo dance in bpf_iter_udp_batch() in patch 4 goes away.

>   
>   	udptable = udp_get_table_afinfo(afinfo, net);
>   
> @@ -3033,10 +3030,7 @@ static struct sock *udp_get_next(struct seq_file *seq, struct sock *sk)
>   	struct udp_seq_afinfo *afinfo;
>   	struct udp_table *udptable;
>   
> -	if (state->bpf_seq_afinfo)
> -		afinfo = state->bpf_seq_afinfo;
> -	else
> -		afinfo = pde_data(file_inode(seq->file));
> +	afinfo = pde_data(file_inode(seq->file));
>   
>   	do {
>   		sk = sk_next(sk);
> @@ -3094,10 +3088,7 @@ void udp_seq_stop(struct seq_file *seq, void *v)
>   	struct udp_seq_afinfo *afinfo;
>   	struct udp_table *udptable;
>   
> -	if (state->bpf_seq_afinfo)
> -		afinfo = state->bpf_seq_afinfo;
> -	else
> -		afinfo = pde_data(file_inode(seq->file));
> +	afinfo = pde_data(file_inode(seq->file));
>   
>   	udptable = udp_get_table_afinfo(afinfo, seq_file_net(seq));
>   
> @@ -3415,28 +3406,11 @@ DEFINE_BPF_ITER_FUNC(udp, struct bpf_iter_meta *meta,
>   
>   static int bpf_iter_init_udp(void *priv_data, struct bpf_iter_aux_info *aux)
>   {
> -	struct udp_iter_state *st = priv_data;
> -	struct udp_seq_afinfo *afinfo;
> -	int ret;
> -
> -	afinfo = kmalloc(sizeof(*afinfo), GFP_USER | __GFP_NOWARN);
> -	if (!afinfo)
> -		return -ENOMEM;
> -
> -	afinfo->family = AF_UNSPEC;
> -	afinfo->udp_table = NULL;
> -	st->bpf_seq_afinfo = afinfo;
> -	ret = bpf_iter_init_seq_net(priv_data, aux);
> -	if (ret)
> -		kfree(afinfo);
> -	return ret;
> +	return bpf_iter_init_seq_net(priv_data, aux);

Nice simplification with the bpf_seq_afinfo cleanup.

>   }
>   
>   static void bpf_iter_fini_udp(void *priv_data)
>   {
> -	struct udp_iter_state *st = priv_data;
> -
> -	kfree(st->bpf_seq_afinfo);
>   	bpf_iter_fini_seq_net(priv_data);
>   }
>