netdev - Re: [PATCH net-next v4 1/2] net sched actions: dump more than TCA_ACT_MAX

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Message-ID: <20170419131323.GE3357@nanopsycho.orion>
Date:   Wed, 19 Apr 2017 15:13:23 +0200
From:   Jiri Pirko <jiri@...nulli.us>
To:     Jamal Hadi Salim <jhs@...atatu.com>
Cc:     davem@...emloft.net, netdev@...r.kernel.org,
        eric.dumazet@...il.com, xiyou.wangcong@...il.com
Subject: Re: [PATCH net-next v4 1/2] net sched actions: dump more than
 TCA_ACT_MAX_PRIO actions per batch

Wed, Apr 19, 2017 at 03:03:59PM CEST, jhs@...atatu.com wrote:
>On 17-04-19 08:36 AM, Jiri Pirko wrote:
>> Wed, Apr 19, 2017 at 01:57:29PM CEST, jhs@...atatu.com wrote:
>> > From: Jamal Hadi Salim <jhs@...atatu.com>
>
>> > include/uapi/linux/rtnetlink.h | 21 +++++++++++++++++++--
>> > net/sched/act_api.c            | 43 ++++++++++++++++++++++++++++++++----------
>> > 3 files changed, 53 insertions(+), 12 deletions(-)
>> > 
>> > diff --git a/include/uapi/linux/rtnetlink.h b/include/uapi/linux/rtnetlink.h
>> > index cce0613..c7080ec 100644
>> > --- a/include/uapi/linux/rtnetlink.h
>> > +++ b/include/uapi/linux/rtnetlink.h
>> > @@ -674,10 +674,27 @@ struct tcamsg {
>> > 	unsigned char	tca__pad1;
>> > 	unsigned short	tca__pad2;
>> > };
>> > +
>> > +enum {
>> > +	TCAA_UNSPEC,
>> > +	TCAA_ACT_TAB,
>> > +	TCAA_ACT_FLAGS,
>> > +	TCAA_ACT_COUNT,
>> > +	__TCAA_MAX
>> > +};
>> > +
>> > +#define TCAA_MAX (__TCAA_MAX - 1)
>> > #define TA_RTA(r)  ((struct rtattr*)(((char*)(r)) + NLMSG_ALIGN(sizeof(struct tcamsg))))
>> > #define TA_PAYLOAD(n) NLMSG_PAYLOAD(n,sizeof(struct tcamsg))
>> > -#define TCA_ACT_TAB 1 /* attr type must be >=1 */	
>> > -#define TCAA_MAX 1
>> > +#define TCA_ACT_TAB TCAA_ACT_TAB
>> 
>> This is mess. What does "TCAA" stand for?
>
>TC Actions Attributes.  What would you call it? I could have
>called it TCA_ROOT etc. But maybe a comment to just call it
>TC Actions Attributes would be enough?

TCA_DUMP_X

it is only for dumping. Naming it "attribute" seems weird. Same as if
you have: int variable_something;


>
>> I suggest some more meaningful naming of the enum items and define
>> TCA_ACT_TAB and TCAA_MAX to the new values in order to maintain UAPI
>
>
>Thats what the above does (for UAPI) maintainance, no?

It does it for TCA_ACT_TAB. We need to do it for both TCA_ACT_TAB and TCAA_MAX


>
>> Also, please put X_MAX = __X_MAX - 1 into enum
>
>That is diverting from the norm which defines it outside
>of the enum. A good reason could be: You, Jiri, plan to go and
>cleanup all the netlink stuff which uses this style.
>Or you think we should start a trend which leads us
>to a new clean style.

I would start now. I can take of the follow-up patch to change the rest.



>
>> 
>> > +/* tcamsg flags stored in attribute TCAA_ACT_FLAGS
>> > + *
>> > + * ACT_LARGE_DUMP_ON user->kernel to request for larger than TCA_ACT_MAX_PRIO
>> > + * actions in a dump. All dump responses will contain the number of actions
>> > + * being dumped stored in for user app's consumption in TCAA_ACT_COUNT
>> > + *
>> > + */
>> > +#define ACT_LARGE_DUMP_ON		(1 << 0)
>> 
>> Use "BIT(0)"
>> 
>
>Same question as before.

Same answer :)


>Are you planning to cleanup the rest of the code which
>follows the same style? example, look at this:
>        TCA_FLOWER_KEY_FLAGS_IS_FRAGMENT = (1 << 0),
>
>
>> Also use the same prefix as for the enum.
>> 
>> + you can have each potential flag as a separate u8 attribute. That is the
>> clearest approach and easily extendable. That's how we do it in devlink
>> for example.
>> 
>
>So you are using 8 bits for one flag which requires one bit?
>+ the TLV header? Sounds like overkill.
>Note: We dont need more than 1 or 2 bits for this case.
>Even 32 bits is overkill for what I am doing.
>When do i need to extend a single bit representation?

I don't see any problem adding couple of bytes if it increases cleannes
and easy extendability.


>
>> 
>> > 	struct net *net = sock_net(skb->sk);
>> > -	struct nlattr *tca[TCA_ACT_MAX + 1];
>> > +	struct nlattr *tca[TCAA_MAX + 1];
>> 
>> This is certainly wrong.
>> 
>
>Why is it wrong?

Because you use existing TCA_ACT_ attr enum.


>
>> 
>> > 	u32 portid = skb ? NETLINK_CB(skb).portid : 0;
>> > 	int ret = 0, ovr = 0;
>> > 
>> > @@ -1005,7 +1014,7 @@ static int tc_ctl_action(struct sk_buff *skb, struct nlmsghdr *n,
>> > 	    !netlink_capable(skb, CAP_NET_ADMIN))
>> > 		return -EPERM;
>> > 
>> > -	ret = nlmsg_parse(n, sizeof(struct tcamsg), tca, TCA_ACT_MAX, NULL,
>> > +	ret = nlmsg_parse(n, sizeof(struct tcamsg), tca, TCAA_MAX, tcaa_policy,
>> 
>> This is certainly wrong.
>> 
>
>Same question as above.

Same answer.


>
>
>> > +		if (nla_put_u32(skb, TCAA_ACT_COUNT, cb->args[1]))
>> > +			goto out_module_put;
>> > +		cb->args[1] = 0;
>> 
>> Why you need to zero this?
>> 
>> 
>
>The count is per submitted message - every time we succesfuly send a msg
>to user, we start the recount.

ok


>
>cheers,
>jamal
>