xdr_count_read_segments(9)

📦 version 7.3.1, in nixpkgs unstable

💅 xdr_count_read_segments — Kernel API Manual, bestie edition ✨

okay so this is a page from the Kernel API Manual (yes, that one, the big serious one) and it's about xdr_count_read_segments, which lowkey has one job and does it slayfully.

🎀 NAME 🎀

xdr_count_read_segments — counts the number of Read segments in a Read list. that's it, that's the whole vibe check 🦋

✨ SYNOPSIS ✨

bool xdr_count_read_segments (struct svc_rdma_recv_ctxt *rctxt , __be32
*p );

🫶 ARGUMENTS 🫶

  • rctxt — the ingress receive context. it's giving "the situation we're looking at" 🌸
  • p — start of an un-decoded Read list. the raw tea, not yet decoded ☕

👑 DESCRIPTION 👑

so the whole point: before allocating anything, make sure the ingress Read list is safe to use. like, don't go spending memory before you know the list isn't gonna jump you. periodt 💅

the segment count is limited to how many segments can fit in the transport header without overflowing the buffer. that's about 40 Read segments for a 1KB inline threshold — literally the ceiling, no cap 🧢

return values, and this part matters so read it:

  • true: the Read list is valid. rctxt's xdr_stream is updated to point to the first byte past the Read list. the rc_read_pcl and rc_call_pcl cl_count fields are set to the number of Read segments in the list. everything's iconic, we move 🎉
  • false: the Read list is corrupt or exceeds the page budget. rctxt's xdr_stream is left in an unknown state 😭 not great, not terrible, just undefined-ish — treat it with suspicion.
fr fr the unknown-state thing is a real one — if you get false, don't go trusting that xdr_stream after, bestie 🙈

🌈 SEE ALSO 🌈

kernel file ./net/sunrpc/xprtrdma/svc_rdma_recvfrom.c — go read the source, iykyk 📖

and that's the page!! sourced from ./net/sunrpc/xprtrdma, dated October 2026, filed under xdr_count_read_segments(9) — catch you in the next manpage, mwah 💖🎀🦋

📦 where this page comes from