netdev - Re: [PATCH bpf-next 2/6] selftests/xsk: Add tail adjustment functionality to XDP

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Message-ID: <Z75GIb_EtzKEKTaY@mini-arch>
Date: Tue, 25 Feb 2025 14:37:21 -0800
From: Stanislav Fomichev <stfomichev@...il.com>
To: "Vyavahare, Tushar" <tushar.vyavahare@...el.com>
Cc: "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"bjorn@...nel.org" <bjorn@...nel.org>,
	"Karlsson, Magnus" <magnus.karlsson@...el.com>,
	"Fijalkowski, Maciej" <maciej.fijalkowski@...el.com>,
	"jonathan.lemon@...il.com" <jonathan.lemon@...il.com>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>,
	"ast@...nel.org" <ast@...nel.org>,
	"daniel@...earbox.net" <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 2/6] selftests/xsk: Add tail adjustment
 functionality to XDP

On 02/25, Vyavahare, Tushar wrote:
> 
> 
> > -----Original Message-----
> > From: Stanislav Fomichev <stfomichev@...il.com>
> > Sent: Thursday, February 20, 2025 11:17 PM
> > To: Vyavahare, Tushar <tushar.vyavahare@...el.com>
> > Cc: bpf@...r.kernel.org; netdev@...r.kernel.org; bjorn@...nel.org; Karlsson,
> > Magnus <magnus.karlsson@...el.com>; Fijalkowski, Maciej
> > <maciej.fijalkowski@...el.com>; jonathan.lemon@...il.com;
> > davem@...emloft.net; kuba@...nel.org; pabeni@...hat.com; ast@...nel.org;
> > daniel@...earbox.net
> > Subject: Re: [PATCH bpf-next 2/6] selftests/xsk: Add tail adjustment functionality
> > to XDP
> > 
> > On 02/20, Tushar Vyavahare wrote:
> > > Introduce a new function, xsk_xdp_adjust_tail, within the XDP program
> > > to adjust the tail of packets. This function utilizes
> > > bpf_xdp_adjust_tail to modify the packet size dynamically based on the 'count'
> > variable.
> > >
> > > If the adjustment fails, the packet is dropped using XDP_DROP to
> > > ensure processing of only correctly modified packets.
> > >
> > > Signed-off-by: Tushar Vyavahare <tushar.vyavahare@...el.com>
> > 
> > Any reason not to combine patches 2..5 into a single one? I looked through each
> > one briefly and it's a bit hard to follow when trying to put everything together..
> 
> Maybe that was too many patches. How about this?
>  
> #1: selftests/xsk: Add packet stream replacement function
> #2: selftests/xsk: Add tail adjustment test functionality to AF_XDP.
> #3: selftests/xsk: Add support check for bpf_xdp_adjust_tail() helper in
>     xskxceiver
> #4: selftests/xsk: Implement and test packet resizing with
>     bpf_xdp_adjust_tail
 
Even that might be too much. #1 is clearly refactoring - keep it separate. The
rest seems like it belongs to the same testcase(s)? I'd put patches 2,3,4,5,6
in the same patch.

For example, you add bpf xsk_xdp_adjust_tail function, but there are
not callers in the same patch, so it's not clear what's the context.
Same for testapp_xdp_adjust_tail - there is no caller, so the reader
needs to go to the next patch to put it all together. Same for
testapp_adjust_tail...