Re: [UPDATED PATCH] Re: [Lse-tech] Re: [Patch 7/7] Generic netlink interface (delay accounting)

[Balbir Singh <balbir@in.ibm.com>]

On Sat, Mar 11, 2006 at 08:30:49AM -0500, jamal wrote:
> On Fri, 2006-10-03 at 22:09 +0530, Balbir Singh wrote:
> > On Fri, Mar 10, 2006 at 09:53:53AM -0500, jamal wrote: 
> 
> > > On kernel->user (in the case of response to #a or async notifiation as
> > > in #b) you really dont need to specify the TG/PID since they appear in
> > > the STATS etc.
> > 
> > I see your point now. I am looking at other users of netlink like
> > rtnetlink and I see the classical usage.
> > 
> > We can implement TLV's in our code, but for the most part the data we exchange
> > between the user <-> kernel has all the TLV's listed in the enum above.
> >
> > The major differnece is the type (pid/tgid). Hence we created a structure
> > (taskstats) instead of using TLV's.
> 
> Something to remember:
> 
> 1) TLVs are essentially giving you the flexibility to send optionally
> appearing elements. It is up to the receiver (in the kernel or user
> space) to check for the presence of mandatory elements or execute things
> depending on the presence of certain TLVs. Example in your case:
> if the tgid TLV appears then the user is requesting for that TLV
> if the pid appears then they are requesting for that
> if both appear then it is the && of the two.
> You should always ignore TLVs you dont understand - to allow for forward
> compatibility.
> 
> 2)  The "T" part is essentially also encoding (semantically) what size
> the value is; the "L" part is useful for validation. So the receiver
> will always know what the size of the TLV is by definition and uses the
> L to make sure it is the right size. Reject what is of the wrong size.
> 
> cheers,
> jamal

Thanks for the clarification, I will try and adapt our genetlink to use
TLV's, I can see the benefits - we will work on this as an evolutionary change
to our code.

Warm Regards,
Balbir