dma_fence_init(9)

📦 version 7.3.1, in nixpkgs unstable

💅 dma_fence_init — the kernel API manual, but make it make sense

okay so bestie, welcome to dma_fence_init(9) from the Kernel API Manual 💖 this one is short but it's important, so grab your iced coffee and let's go ✨

🎀 NAME 🎀

dma_fence_init — initialize a custom fence. that's it, that's the whole vibe 🦋

✨ SYNOPSIS ✨

void dma_fence_init (struct dma_fence *fence , const struct
dma_fence_ops *ops , spinlock_t *lock , u64 context , u64 seqno );

literally just one function call, no drama 💅

🌸 ARGUMENTS 🌸

  • fence — the fence you're initializing. the main character, the one getting set up 👑
  • ops — the dma_fence_ops that says what operations apply to this fence. it's giving "here's my instruction manual" 🎀
  • lock — an optional irqsafe spinlock used for locking this fence. optional!! remember that word, it comes back later 🔥
  • context — the execution context this fence runs on
  • seqno — a linear increasing sequence number for this context. linear!! increasing!! no take-backs 📈

💜 DESCRIPTION 💜

so this is what actually initializes an allocated fence. and here's the cute part: the caller doesn't have to keep its refcount after committing with this fence 🫶 — BUT (and yes there's a but, there's always a but 😭) it will need to hold a refcount again if dma_fence_ops.enable_signaling gets called. so like... remember your refcount exists, bestie. don't ghost it.

context and seqno are the whole reason comparing fences is easy — they let you check which fence is later by simply using dma_fence_later. convenient?? obsessed 💖

now the serious bit, no cap: external locks are a relic of legacy use cases that needed a shared lock to serialize signaling when out-of-order signaling wasn't possible through dma_fence_ops.signaled. drivers have fully abandoned this concept since the callback got introduced, but the external lock is still around 💀 it's giving "haunted artifact in the codebase."

new users MUST NOT use external locks 🚨 fr fr, because they force the issuer to outlive all fences that reference the lock. that's not a vibe. do not do it. periodt 💅

🦋 SEE ALSO 🦋

the whole friend group, in order:

and that's the page!! 🫶 this lil guy lives in ./drivers/dma-buf, dated October 2026, and honestly? iconic. go initialize a fence responsibly, bestie. slay 💅✨🌈

📦 where this page comes from