Re: [PATCH libnetfilter_queue v2] src: Add faster alternatives to pktb_alloc()

[Pablo Neira Ayuso <pablo@netfilter.org>]

On Sat, Feb 01, 2020 at 05:21:27PM +1100, Duncan Roe wrote:
> Functions pktb_alloc_data, pktb_make and pktb_make_data are defined.
> The pktb_make pair are syggested as replacements for the pktb_alloc (now) pair
> because they are always faster.
> 
> - Add prototypes to include/libnetfilter_queue/pktbuff.h
> - Add pktb_alloc_data much as per Pablo's email of Wed, 8 Jan 2020
>   speedup: point to packet data in netlink receive buffer rather than copy to
>            area immediately following pktb struct
> - Add pktb_make much like pktb_usebuf proposed on 10 Dec 2019
>   2 sppedups: 1. Use an existing buffer rather than calloc and (later) free one.
>               2. Only zero struct and extra parts of pktb - the rest is
>                  overwritten by copy (calloc has to zero the lot).
> - Add pktb_make_data
>   3 speedups: All of the above
> - Document the new functions
> - Move pktb_alloc and pktb_alloc_data into the "other functions" group since
>   they are slower than the "make" equivalent functions
> 
> Signed-off-by: Duncan Roe <duncan_roe@optusnet.com.au>
> ---
>  include/libnetfilter_queue/pktbuff.h |   3 +
>  src/extra/pktbuff.c                  | 296 ++++++++++++++++++++++++++++++-----
>  2 files changed, 261 insertions(+), 38 deletions(-)
> 
> diff --git a/include/libnetfilter_queue/pktbuff.h b/include/libnetfilter_queue/pktbuff.h
> index 42bc153..fc6bf01 100644
> --- a/include/libnetfilter_queue/pktbuff.h
> +++ b/include/libnetfilter_queue/pktbuff.h
> @@ -4,6 +4,9 @@
>  struct pkt_buff;
>  
>  struct pkt_buff *pktb_alloc(int family, void *data, size_t len, size_t extra);
> +struct pkt_buff *pktb_alloc_data(int family, void *data, size_t len);
> +struct pkt_buff *pktb_make(int family, void *data, size_t len, size_t extra, void *buf, size_t bufsize);
> +struct pkt_buff *pktb_make_data(int family, void *data, size_t len, void *buf, size_t bufsize);

Hm, when I delivered the patch to you, I forgot that you main point
was that you wanted to skip the memory allocation.

I wonder if all these new functions can be consolidated into one
single function, something like:

        struct pkt_buff *pktb_alloc2(int family, void *head, size_t head_size, void *data, size_t len, size_t extra);

The idea is that:

* head is the memory area that is large enough for the struct pkt_buff
  (metadata). You can add a new pktb_head_size() function that returns
  the size of opaque struct pkt_buff structure (whose layout is not
  exposed to the user). I think you can this void *buf in your pktb_make
  function.

* data is the memory area to store the network packet itself.

Then, you can allocate head and data in the stack and skip
malloc/calloc.

Would this work for you? I would prefer if there is just one single
advanced function to do this.

Thanks for your patience.