netdev - Re: [PATCH RFC v2 net-next 01/25] net/netlink: Pass extack to dump callbacks

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Message-ID: <20181002110738.3jxivgmv56cmgtvj@brauner.io>
Date:   Tue, 2 Oct 2018 13:07:39 +0200
From:   Christian Brauner <christian@...uner.io>
To:     David Ahern <dsahern@...nel.org>
Cc:     netdev@...r.kernel.org, davem@...emloft.net, jbenc@...hat.com,
        stephen@...workplumber.org, David Ahern <dsahern@...il.com>
Subject: Re: [PATCH RFC v2 net-next 01/25] net/netlink: Pass extack to dump
 callbacks

On Mon, Oct 01, 2018 at 05:28:27PM -0700, David Ahern wrote:
> From: David Ahern <dsahern@...il.com>
> 
> Pass extack to dump callbacks by adding extack to netlink_dump_control,
> transferring to netlink_callback and adding to the netlink_dump. Update
> rtnetlink as the first user. Update netlink_dump to add any message after
> the dump_done_errno.
> 
> Signed-off-by: David Ahern <dsahern@...il.com>

This makes sense to me as it would allow us to report back more
meaningful errors to userspace.

> ---
>  include/linux/netlink.h  |  2 ++
>  net/core/rtnetlink.c     |  1 +
>  net/netlink/af_netlink.c | 20 +++++++++++++++-----
>  3 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/netlink.h b/include/linux/netlink.h
> index 71f121b66ca8..8fc90308a653 100644
> --- a/include/linux/netlink.h
> +++ b/include/linux/netlink.h
> @@ -176,6 +176,7 @@ struct netlink_callback {
>  	void			*data;
>  	/* the module that dump function belong to */
>  	struct module		*module;
> +	struct netlink_ext_ack	*extack;
>  	u16			family;
>  	u16			min_dump_alloc;
>  	unsigned int		prev_seq, seq;
> @@ -197,6 +198,7 @@ struct netlink_dump_control {
>  	int (*done)(struct netlink_callback *);
>  	void *data;
>  	struct module *module;
> +	struct netlink_ext_ack *extack;
>  	u16 min_dump_alloc;
>  };
>  
> diff --git a/net/core/rtnetlink.c b/net/core/rtnetlink.c
> index 35162e1b06ad..da91b38297d3 100644
> --- a/net/core/rtnetlink.c
> +++ b/net/core/rtnetlink.c
> @@ -4689,6 +4689,7 @@ static int rtnetlink_rcv_msg(struct sk_buff *skb, struct nlmsghdr *nlh,
>  				.dump		= dumpit,
>  				.min_dump_alloc	= min_dump_alloc,
>  				.module		= owner,
> +				.extack		= extack
>  			};
>  			err = netlink_dump_start(rtnl, skb, nlh, &c);
>  			/* netlink_dump_start() will keep a reference on
> diff --git a/net/netlink/af_netlink.c b/net/netlink/af_netlink.c
> index e3a0538ec0be..7094156c94f0 100644
> --- a/net/netlink/af_netlink.c
> +++ b/net/netlink/af_netlink.c
> @@ -129,7 +129,7 @@ static const char *const nlk_cb_mutex_key_strings[MAX_LINKS + 1] = {
>  	"nlk_cb_mutex-MAX_LINKS"
>  };
>  
> -static int netlink_dump(struct sock *sk);
> +static int netlink_dump(struct sock *sk, struct netlink_ext_ack *extack);
>  
>  /* nl_table locking explained:
>   * Lookup and traversal are protected with an RCU read-side lock. Insertion
> @@ -1981,7 +1981,7 @@ static int netlink_recvmsg(struct socket *sock, struct msghdr *msg, size_t len,
>  
>  	if (nlk->cb_running &&
>  	    atomic_read(&sk->sk_rmem_alloc) <= sk->sk_rcvbuf / 2) {
> -		ret = netlink_dump(sk);
> +		ret = netlink_dump(sk, NULL);
>  		if (ret) {
>  			sk->sk_err = -ret;
>  			sk->sk_error_report(sk);
> @@ -2168,7 +2168,7 @@ EXPORT_SYMBOL(__nlmsg_put);
>   * It would be better to create kernel thread.
>   */
>  
> -static int netlink_dump(struct sock *sk)
> +static int netlink_dump(struct sock *sk, struct netlink_ext_ack *extack)
>  {
>  	struct netlink_sock *nlk = nlk_sk(sk);
>  	struct netlink_callback *cb;
> @@ -2222,8 +2222,11 @@ static int netlink_dump(struct sock *sk)
>  	skb_reserve(skb, skb_tailroom(skb) - alloc_size);
>  	netlink_skb_set_owner_r(skb, sk);
>  
> -	if (nlk->dump_done_errno > 0)
> +	if (nlk->dump_done_errno > 0) {
> +		cb->extack = extack;
>  		nlk->dump_done_errno = cb->dump(skb, cb);
> +		cb->extack = NULL;
> +	}
>  
>  	if (nlk->dump_done_errno > 0 ||
>  	    skb_tailroom(skb) < nlmsg_total_size(sizeof(nlk->dump_done_errno))) {
> @@ -2246,6 +2249,12 @@ static int netlink_dump(struct sock *sk)
>  	memcpy(nlmsg_data(nlh), &nlk->dump_done_errno,
>  	       sizeof(nlk->dump_done_errno));
>  
> +	if (extack && extack->_msg && nlk->flags & NETLINK_F_EXT_ACK) {
> +		nlh->nlmsg_flags |= NLM_F_ACK_TLVS;
> +		if (!nla_put_string(skb, NLMSGERR_ATTR_MSG, extack->_msg))
> +			nlmsg_end(skb, nlh);
> +	}
> +
>  	if (sk_filter(sk, skb))
>  		kfree_skb(skb);
>  	else
> @@ -2307,6 +2316,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
>  	cb->module = control->module;
>  	cb->min_dump_alloc = control->min_dump_alloc;
>  	cb->skb = skb;
> +	cb->extack = control->extack;
>  
>  	if (control->start) {
>  		ret = control->start(cb);
> @@ -2319,7 +2329,7 @@ int __netlink_dump_start(struct sock *ssk, struct sk_buff *skb,
>  
>  	mutex_unlock(nlk->cb_mutex);
>  
> -	ret = netlink_dump(sk);
> +	ret = netlink_dump(sk, cb->extack);
>  
>  	sock_put(sk);
>  
> -- 
> 2.11.0
>