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charset=UTF-8 Content-Transfer-Encoding: 8bit > Any reason you're not reading the real value from > /proc/sys/net/core/max_skb_frags ? The test wants to exercise the maximum supported number of frames, but also needs to run on every build. CONFIG_MAX_SKB_FRAGS ranges from 17 to 45, so using the minimum (17, i.e. 18 frames) gives the largest bound that works everywhere. af_xdp.rst documents the same limit: "For copy mode, the maximum supported number of frames in a packet is equal to CONFIG_MAX_SKB_FRAGS + 1." xsk checks MAX_SKB_FRAGS directly (net/xdp/xsk.c), not net.core.max_skb_frags. I also set net.core.max_skb_frags=4 and ran xdp_metadata; it still passes, which confirms xsk does not consume that sysctl. Reading it in this test would not tell us the xsk limit, and would only reduce coverage if it is lowered. CONFIG_MAX_SKB_FRAGS is compile-time and has no userspace interface, so 18 frames is the portable upper bound. That is why I used 17. Thanks, Rongzheng