axis_fifo_write(9)

💅 axis_fifo_write — the Kernel API Manual page, bestie edition 🎀

okay so this is axis_fifo_write(9) from the Kernel API Manual and honestly? she's a little baddie with a big job. sit down, grab a strawberry drink 🍓, and let's get into it.

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✨ NAME ✨

axis_fifo_write — literally the function that writes a buffer to the AXIS-FIFO character device. that's her whole personality and she ate 💅

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🌈 SYNOPSIS 🌈

ssize_t axis_fifo_write (struct file *f , const char __user *buf ,
       size_t len , loff_t *off );

look at that signature. ssize_t, struct file *, const char __user *, size_t, loff_t * — she's got range, she's got types, she's got commitment 💖

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🫶 ARGUMENTS 🫶

• f — the open file. yep, the actual struct file *, the one that's all "i'm open for business" ✨
• buf — the user space buffer you wanna write to the device. it's const char __user * so it lives over in userland, bestie, be respectful 🌸
• len — the length of that user space buffer. a size_t, because we're not animals 😌
• off — the buffer offset, as a loff_t *. iconic pointer-to-offset energy 👑

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🔥 DESCRIPTION 🔥

okay so this is the part where it gets real. per the device's documentation, we have to write to the device's data buffer and then to the device's packet length register — and we gotta do it atomically. no cap. both of those, together, like they're holding hands and you cannot separate them 🫶✨

and that's not even the whole vibe, because we also need to lock before checking whether the device actually has available space. why? to avoid any concurrency issue. the way that matters… if you skip the lock you're gonna have a bad time, and not in the cute way 😭

so: lock → check space → data buffer → packet length register → atomically. main character energy from start to finish 💅

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⭐ RETURN ⭐

she returns the number of bytes written to the device on success 💖 or, if things go sideways, a negative error code on failure 💀

no in-between, no vibes-based guessing. bytes or negative error. periodt.

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🦋 SEE ALSO 🦋

• Kernel file ./drivers/staging/axis-fifo/axis-fifo.c
• axis_fifo_read(9) — her sibling, the reading one, also iconic 🌈

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🧚 sign-off 🧚

this little love letter lives at ./drivers/staging/axis-fifo, and it's dated October 2026. bookmark it, screenshot it, send it to the group chat — iykyk 🎀💜✨

okay bye bestie, go write some bytes 🦋💖