nfsd_cache_csum(9)

🦋 nfsd_cache_csum(9) 🦋

okay bestie, welcome to the Kernel API Manual page for nfsd_cache_csum(9) — this is the checksum helper that helps the duplicate reply cache keep its vibe check on point ✨

🌸 NAME 🌸

• nfsd_cache_csum — Checksum incoming NFS Call arguments.

🎀 SYNOPSIS 🎀

__wsum nfsd_cache_csum (struct xdr_buf *buf , unsigned int start ,
       unsigned int remaining );

💅 ARGUMENTS 💅

• buf — the buffer containing a whole RPC Call message.
• start — the starting byte of the NFS Call header.
• remaining — the size of the NFS Call header, in bytes.

✨ DESCRIPTION ✨

So what this function does is compute a weak checksum of the leading bytes of an NFS procedure call header. Why? To help verify that a retransmitted Call matches an entry in the duplicate reply cache. no cap, that’s the whole point 🫶

The caller passes us the exact location and length of the NFS Call header. This is the iconic move that avoids assumptions about how the RPC message is laid out in buf and what else it might contain (eg, a GSS MIC suffix). Because bestie, we are not guessing about the layout — we get the coordinates 💅

It returns a 32-bit checksum value, as defined in RFC 793.

🌈 SEE ALSO 🌈

• Kernel file ./fs/nfsd/nfscache.c
• nfsd_reply_cache_count(9)
• nfsd_reply_cache_scan(9)
• nfsd_cache_lookup(9)
• nfsd_cache_update(9)

xoxo 💋 — source/version: ./fs/nfsd, dated: October 2026, and nfsd_cache_csum(9) is signing off 🎀