Re: [PATCH v2 net-next 1/7] bpf: add 'flags' attribute to BPF_MAP_UPDATE_ELEM command

[Hannes Frederic Sowa <hannes@stressinduktion.org>]

On Fr, 2014-11-14 at 07:33 -0800, Alexei Starovoitov wrote:
> On Fri, Nov 14, 2014 at 4:11 AM, Hannes Frederic Sowa
> <hannes@stressinduktion.org> wrote:
> > On Do, 2014-11-13 at 17:36 -0800, Alexei Starovoitov wrote:
> >> the current meaning of BPF_MAP_UPDATE_ELEM syscall command is:
> >> either update existing map element or create a new one.
> >> Initially the plan was to add a new command to handle the case of
> >> 'create new element if it didn't exist', but 'flags' style looks
> >> cleaner and overall diff is much smaller (more code reused), so add 'flags'
> >> attribute to BPF_MAP_UPDATE_ELEM command with the following meaning:
> >>  #define BPF_ANY      0 /* create new element or update existing */
> >>  #define BPF_NOEXIST  1 /* create new element if it didn't exist */
> >>  #define BPF_EXIST    2 /* update existing element */
> >
> > Would a cmpxchg-alike function be handy here?
> 
> you mean cmpxchg command in addition to
> update() command ?
> May be... it will have an extra 'value' argument
> (key, old_value, new_value)
> I don't have a use case for it yet though.

I don't neither. ;)

I just wanted to bring this up before user space api might get public
and the additional argument might make problems.

Bye,
Hannes