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program-type/BPF_PROG_TYPE_SOCK_OPS: add mention of BPF_WRITE_HDR_TCP_CURRENT_MSS #290

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Merged
dylandreimerink merged 1 commit into from
Sep 3, 2026
Merged

program-type/BPF_PROG_TYPE_SOCK_OPS: add mention of BPF_WRITE_HDR_TCP_CURRENT_MSS #290

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1 change: 1 addition & 0 deletions docs/linux/program-type/BPF_PROG_TYPE_SOCK_OPS.md
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Expand Up @@ -175,6 +175,7 @@ When the `BPF_SOCK_OPS_WRITE_HDR_OPT_CB_FLAG` flag is set with [`bpf_sock_ops_cb
The arguments in the context will have the following meanings:

* `args[0]`: bool want_cookie. (in writing SYNACK only)
* `args[0]`: (when not writing SYNACK) If equal to `BPF_WRITE_HDR_TCP_CURRENT_MSS`, the kernel will use the `bpf_reserve_hdr_opt()` call to guess the future packet's size and not actually reserve memory. The skb passed as a parameter is empty dummy and no subsequent `BPF_SOCK_OPS_WRITE_HDR_OPT_CB` event will occur.

`sock_ops->skb_data`: Not available because no header has been written yet.

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