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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