STRUCT VGETRANDOM_STATE(9)

okay so welcome to the struct vgetrandom_state page, bestie — this is from the Kernel API Manual, section 9, and it’s giving kernel-internals glam 💅✨

✨ NAME ✨

struct vgetrandom_state — State used by vDSO getrandom().

🦋 SYNOPSIS 🦋

here’s the whole struct, no edits, no cap:

       struct vgetrandom_state {
           union {
             struct {
               u8 batch[CHACHA_BLOCK_SIZE * 3 / 2];
               u32 key[CHACHA_KEY_SIZE / sizeof(u32)];
             };
             u8 batch_key[CHACHA_BLOCK_SIZE * 2];
           };
           u64 generation;
           u8 pos;
           bool in_use;
        };

🎀 Members 🎀

okay bestie, let’s meet the members one by one — they all matter, fr fr 🫶

• {unnamed_union} — anonymous. literally a union with no name, just vibing.
• {unnamed_struct} — anonymous. same energy for the nested struct.
• batch — One and a half ChaCha20 blocks of buffered RNG output. iconic little buffer 💖
• key — Key to be used for generating next batch.
• batch_key — Union of the prior two members, which is exactly two full ChaCha20 blocks in size, so that batch and key can be filled together.
• generation — Snapshot of rng_info->generation in the vDSO data page at the time key was generated.
• pos — Offset into batch of the next available random byte.
• in_use — Reentrancy guard for reusing a state within the same thread due to signal handlers.

🌈 SEE ALSO 🌈

• Kernel file ./include/vdso/getrandom.h
• __arch_chacha20_blocks_nostack(9), __vdso_getrandom(9)

that’s the whole vibe check, bestie 🫶 — source/version: ./include/vdso, date: October 2026. stay hydrated, keep your unions anonymous if you want, and never skip the reentrancy guard 💜🔥