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This provides a generic SKB based non-optimized XDP path which is used if either the driver lacks a specific XDP implementation, or the user requests it via a new IFLA_XDP_FLAGS value named XDP_FLAGS_SKB_MODE. It is arguable that perhaps I should have required something like this as part of the initial XDP feature merge. I believe this is critical for two reasons: 1) Accessibility. More people can play with XDP with less dependencies. Yes I know we have XDP support in virtio_net, but that just creates another depedency for learning how to use this facility. I wrote this to make life easier for the XDP newbies. 2) As a model for what the expected semantics are. If there is a pure generic core implementation, it serves as a semantic example for driver folks adding XDP support. One thing I have not tried to address here is the issue of XDP_PACKET_HEADROOM, thanks to Daniel for spotting that. It seems incredibly expensive to do a skb_cow(skb, XDP_PACKET_HEADROOM) or whatever even if the XDP program doesn't try to push headers at all. I think we really need the verifier to somehow propagate whether certain XDP helpers are used or not. v5: - Handle both negative and positive offset after running prog - Fix mac length in XDP_TX case (Alexei) - Use rcu_dereference_protected() in free_netdev (kbuild test robot) v4: - Fix MAC header adjustmnet before calling prog (David Ahern) - Disable LRO when generic XDP is installed (Michael Chan) - Bypass qdisc et al. on XDP_TX and record the event (Alexei) - Do not perform generic XDP on reinjected packets (DaveM) v3: - Make sure XDP program sees packet at MAC header, push back MAC header if we do XDP_TX. (Alexei) - Elide GRO when generic XDP is in use. (Alexei) - Add XDP_FLAG_SKB_MODE flag which the user can use to request generic XDP even if the driver has an XDP implementation. (Alexei) - Report whether SKB mode is in use in rtnl_xdp_fill() via XDP_FLAGS attribute. (Daniel) v2: - Add some "fall through" comments in switch statements based upon feedback from Andrew Lunn - Use RCU for generic xdp_prog, thanks to Johannes Berg. Tested-by: Andy Gospodarek <andy@greyhouse.net> Tested-by: Jesper Dangaard Brouer <brouer@redhat.com> Tested-by: David Ahern <dsa@cumulusnetworks.com> Signed-off-by: David S. Miller <davem@davemloft.net>
Linux kernel ============ This file was moved to Documentation/admin-guide/README.rst Please notice that there are several guides for kernel developers and users. These guides can be rendered in a number of formats, like HTML and PDF. In order to build the documentation, use ``make htmldocs`` or ``make pdfdocs``. There are various text files in the Documentation/ subdirectory, several of them using the Restructured Text markup notation. See Documentation/00-INDEX for a list of what is contained in each file. Please read the Documentation/process/changes.rst file, as it contains the requirements for building and running the kernel, and information about the problems which may result by upgrading your kernel.