Messages in this thread | | | Subject | Re: [RFC][UPDATED PATCH 2.6.16] [Patch 9/9] Generic netlink interface for delay accounting | From | jamal <> | Date | Sat, 25 Mar 2006 07:52:13 -0500 |
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On Sat, 2006-25-03 at 15:11 +0530, Balbir Singh wrote:
> > Thanks for the advice, I will dive into nesting. I could not find any > in tree users who use nesting, so I have a few questions >
Hrm - I have to say i am suprised theres nothing; i could have sworn Thomas had done some conversions already.
> nla_nest_start() accepts two parameters an skb and an attribute type. > Do I have to create a new attribute type like TASKSTATS_TYPE_AGGR to > contain the nested attributes > > TASKSTATS_TYPE_AGGR > TASKSTATS_TYPE_PID/TGID > TASKSTATS_TYPE_STATS > > > but this will lead to > > TASKSTATS_TYPE_AGGR > TASKSTATS_TYPE_PID > TASKSTATS_TYPE_STATS > TASKSTATS_TYPE_AGGR > TASKSTATS_TYPE_TGID > TASKSTATS_TYPE_STATS > > being returned from taskstats_exit_pid(). >
no this is wrong by virtue of having TASKSTATS_TYPE_AGGR twice. Again invoke the rule i cited earlier. What you could do instead is a second AGGR; and your nesting would be:
TASKSTATS_TYPE_AGGR1 <--- nest start with this type TASKSTATS_TYPE_PID <-- NLA_U32_PUT TASKSTATS_TYPE_STATS <-- NAL_PUT_TYPE <-- nest end of TASKSTATS_TYPE_AGGR1 TASKSTATS_TYPE_AGGR2 <--- nest start with this type TASKSTATS_TYPE_TGID <-- NLA_U32_PUT TASKSTATS_TYPE_STATS <-- NAL_PUT_TYPE <-- nest end of TASKSTATS_TYPE_AGGR2
> The other option is to nest > > TASKSTATS_TYPE_PID/TGID > TASKSTATS_TYPE_STATS >
The advantage being you dont introduce another T.
> but the problem with this approach is, nla_len contains the length of > all attributes including the nested attribute. So it is hard to find > the offset of TASKSTATS_TYPE_STATS in the buffer. >
So you would distinguish the two as have something like:
TASKSTATS_TYPE_PID u32 pid TASKSTATS_TYPE_STATS TASKSTATS_TYPE_TGID u32 tgid TASKSTATS_TYPE_STATS or TASKSTATS_TYPE_PID u32 pid TASKSTATS_TYPE_TGID u32 tgid
both should be fine. The difference between the two is the length in the second case will be 4 and in the other case will be larger.
But come to think of it, this will introduce unneeded semantics; you have very few items to do, so forget it. Go with scheme #1 but change the names to TASKSTATS_TYPE_AGGR_PID and TASKSTATS_TYPE_AGGR_TGID.
cheers, jamal
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