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

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Message-ID: <20170419155400.GH3357@nanopsycho.orion>
Date:   Wed, 19 Apr 2017 17:54:00 +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 05:37:15PM CEST, jhs@...atatu.com wrote:
>On 17-04-19 09:13 AM, Jiri Pirko wrote:
>> 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(-)
>
>> > > > +#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;
>> 
>
>Jiri, this is not just for dumping. We are describing high level
>attributes for tc actions.

This is already present:
enum {
        TCA_ACT_UNSPEC,
        TCA_ACT_KIND,
        TCA_ACT_OPTIONS,
        TCA_ACT_INDEX,
        TCA_ACT_STATS,
        TCA_ACT_PAD,
        TCA_ACT_COOKIE,
        __TCA_ACT_MAX
};

This is nested inside the dump message (TCAA_MAX, TCA_ACT_TAB)

Looks like you are mixing these 2.



>
>> 
>> > 
>> > > 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
>> 
>
>TCAA_XXX is the namespace selected. You dont like that name and
>adding DUMP doesnt make sense to me. How about TCA_ACT_ROOT?
>
>> > 
>> > > 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.
>> 
>
>It is a _lot_ of code to change! Note:
>This is all the UAPI visible code (the same coding style for 20 years).
>I am worried about this part.

We'll see. Lets do it in a sensitive way, in steps. But for new things,
I think it is good not to stick with old and outlived habits.


>
>> > > 
>> > > > +/* 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 :)
>> 
>
>I will change this one - it is a lot simpler coding style
>wide/wise than the other one.
>
>> > Are you planning to cleanup the rest of the code which
>
>> > 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.
>> 
>
>How do you extend one bit? Seriously. If i want to add another bit I
>will add one more to existing bit map not 64 (T + L + 8bits + pad).
>If i ran out of space i will add a new TLV.

Netlink is TLV, should be used as TLV. I don't see how you can run out
any space. You tend to use Netlink in some weird hybrid mode, with only
argument being space. I think that couple of bytes wasted is not
a problem at all...


>
>> > > 
>> > > > 	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.
>> 
>
>Is there a programming mistake or you  just dont like the name?
>AFAIK, and based on my testing that code is correct.

See my first comment. I think that you mix 2 things together.


>
>> > > > -	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.
>> 
>
>And same question still.
>
>cheers,
>jamal