netdev - Re: [PATCH bpf-next] net: xdp: introduce xdp_init

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Message-ID: <721648a5e14dadc32629291a7d1914dd1044b7d0.camel@kernel.org>
Date:   Thu, 10 Dec 2020 10:49:05 -0800
From:   Saeed Mahameed <saeed@...nel.org>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>
Cc:     Lorenzo Bianconi <lorenzo@...nel.org>, bpf@...r.kernel.org,
        netdev@...r.kernel.org, davem@...emloft.net, kuba@...nel.org,
        ast@...nel.org, daniel@...earbox.net, brouer@...hat.com,
        alexander.duyck@...il.com
Subject: Re: [PATCH bpf-next] net: xdp: introduce xdp_init_buff utility
 routine

On Thu, 2020-12-10 at 18:59 +0100, Lorenzo Bianconi wrote:
> On Dec 10, Maciej Fijalkowski wrote:
> > On Thu, Dec 10, 2020 at 05:32:41PM +0100, Lorenzo Bianconi wrote:
> > > > On Thu, Dec 10, 2020 at 04:50:42PM +0100, Lorenzo Bianconi
> > > > wrote:
> > > > > Introduce xdp_init_buff utility routine to initialize
> > > > > xdp_buff data
> > > > > structure. Rely on xdp_init_buff in all XDP capable drivers.
> > > > 
> > > > Hm, Jesper was suggesting two helpers, one that you implemented
> > > > for things
> > > > that are set once per NAPI and the other that is set per each
> > > > buffer.
> > > > 
> > > > Not sure about the naming for a second one - xdp_prepare_buff ?
> > > > xdp_init_buff that you have feels ok.
> > > 
> > > ack, so we can have xdp_init_buff() for initialization done once
> > > per NAPI run and 
> > > xdp_prepare_buff() for per-NAPI iteration initialization, e.g.
> > > 
> > > static inline void
> > > xdp_prepare_buff(struct xdp_buff *xdp, unsigned char *hard_start,
> > > 		 int headroom, int data_len)
> > > {
> > > 	xdp->data_hard_start = hard_start;
> > > 	xdp->data = hard_start + headroom;
> > > 	xdp->data_end = xdp->data + data_len;
> > > 	xdp_set_data_meta_invalid(xdp);
> > > }
> > 
> > I think we should allow for setting the data_meta as well.
> > x64 calling convention states that first four args are placed onto
> > registers, so to keep it fast maybe have a third helper:
> > 
> > static inline void
> > xdp_prepare_buff_meta(struct xdp_buff *xdp, unsigned char
> > *hard_start,
> > 		      int headroom, int data_len)
> > {
> > 	xdp->data_hard_start = hard_start;
> > 	xdp->data = hard_start + headroom;
> > 	xdp->data_end = xdp->data + data_len;
> > 	xdp->data_meta = xdp->data;
> > }
> > 
> > Thoughts?
> 
> ack, I am fine with it. Let's wait for some feedback.
> 
> Do you prefer to have xdp_prepare_buff/xdp_prepare_buff_meta in the
> same series
> of xdp_buff_init() or is it ok to address it in a separate patch?
> 

you only need 2
why do you need xpd_prepare_buff_meta? that's exactly
what xdp_set_data_meta_invalid(xdp) is all about.