On Fri, Mar 24, 2006 at 08:19:25PM -0500, jamal wrote:

On Fri, 2006-24-03 at 20:24 +0530, Balbir Singh wrote:

quoted

Hmm... Would it be ok to send one message with the following format

1. TLV=TASKSTATS_TYPE_PID
2. TLV=TASKSTATS_TYPE_STATS
3. TLV=TASKSTATS_TYPE_TGID
4. TLV=TASKSTATS_TYPE_STATS

It would still be one message, except that 3 and 4 would be optional.
What do you think?

No, that wont work since #2 and #4 are basically the same TLV. [Recall
that "T" is used to index an array]. Your other alternative is to have
#4 perhaps called TASKSTATS_TGID_STATS and #2 TASKSTATS_PID_STATS
although that would smell a little.
Dont be afraid to do the nest, it will be a little painful initially but
i am sure once you figure it out you will appreciate it.

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

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().

The other option is to nest

TASKSTATS_TYPE_PID/TGID
   TASKSTATS_TYPE_STATS

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.

Do I understand NLA nesting at all? May be I am missing something obvious.

Thanks,
Balbir