netdev - Re: [PATCH net-next] net: ethernet: enetc: set frag flag for non-linear xdp buffers

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Date:   Tue, 6 Dec 2022 14:35:52 +0200
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     netdev@...r.kernel.org, claudiu.manoil@....com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, lorenzo.bianconi@...hat.com
Subject: Re: [PATCH net-next] net: ethernet: enetc: set frag flag for
 non-linear xdp buffers

Hi Lorenzo,

On Sun, Dec 04, 2022 at 11:33:23PM +0100, Lorenzo Bianconi wrote:
> Set missing XDP_FLAGS_HAS_FRAGS bit in enetc_add_rx_buff_to_xdp for
> non-linear xdp buffers.
> 
> Fixes: d1b15102dd16 ("net: enetc: add support for XDP_DROP and XDP_PASS")

This can't be the Fixes: tag, struct xdp_buff didn't even have a "flags"
field when that commit was introduced.

Also, what does this change aim to achieve? It has a Fixes: tag but it's
aimed for net-next. Is it to enable multi-buff XDP support? But we also
have this in place, shouldn't that be deleted too?

		case XDP_REDIRECT:
			/* xdp_return_frame does not support S/G in the sense
			 * that it leaks the fragments (__xdp_return should not
			 * call page_frag_free only for the initial buffer).
			 * Until XDP_REDIRECT gains support for S/G let's keep
			 * the code structure in place, but dead. We drop the
			 * S/G frames ourselves to avoid memory leaks which
			 * would otherwise leave the kernel OOM.
			 */
			if (unlikely(cleaned_cnt - orig_cleaned_cnt != 1)) {
				enetc_xdp_drop(rx_ring, orig_i, i);
				rx_ring->stats.xdp_redirect_sg++;
				break;
			}