netdev - Re: [PATCH v2 bpf-next 2/8] drivers: net: turn on XDP features

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Date:   Tue, 24 Jan 2023 19:04:14 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Lorenzo Bianconi <lorenzo@...nel.org>
Cc:     bpf@...r.kernel.org, netdev@...r.kernel.org, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, davem@...emloft.net,
        hawk@...nel.org, pabeni@...hat.com, edumazet@...gle.com,
        toke@...hat.com, memxor@...il.com, alardam@...il.com,
        saeedm@...dia.com, anthony.l.nguyen@...el.com, gospo@...adcom.com,
        vladimir.oltean@....com, nbd@....name, john@...ozen.org,
        leon@...nel.org, simon.horman@...igine.com, aelior@...vell.com,
        christophe.jaillet@...adoo.fr, ecree.xilinx@...il.com,
        mst@...hat.com, bjorn@...nel.org, magnus.karlsson@...el.com,
        maciej.fijalkowski@...el.com, intel-wired-lan@...ts.osuosl.org,
        lorenzo.bianconi@...hat.com, martin.lau@...ux.dev
Subject: Re: [PATCH v2 bpf-next 2/8] drivers: net: turn on XDP features

On Wed, 25 Jan 2023 01:33:22 +0100 Lorenzo Bianconi wrote:
> A summary of the flags being set for various drivers is given below.
> Note that XDP_F_REDIRECT_TARGET and XDP_F_FRAG_TARGET are features
> that can be turned off and on at runtime. This means that these flags
> may be set and unset under RTNL lock protection by the driver. Hence,
> READ_ONCE must be used by code loading the flag value.
> 
> Also, these flags are not used for synchronization against the availability
> of XDP resources on a device. It is merely a hint, and hence the read
> may race with the actual teardown of XDP resources on the device. This
> may change in the future, e.g. operations taking a reference on the XDP
> resources of the driver, and in turn inhibiting turning off this flag.
> However, for now, it can only be used as a hint to check whether device
> supports becoming a redirection target.

Acked-by: Jakub Kicinski <kuba@...nel.org>