STRUCT EF4_SPECIAL_BUFFER(9)

🎀 struct ef4_special_buffer(9) 🎀

ok so this is a page from the Kernel API Manual, and bestie, we're about to get into it — it's all about struct ef4_special_buffer, aka the DMA buffer that gets entered into the buffer table. yes, that's the whole vibe. let's go 💅

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✨ NAME ✨

struct ef4_special_buffer — a DMA buffer that's been entered into the buffer table 🫶

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🌸 SYNOPSIS 🌸

struct ef4_special_buffer {
    struct ef4_buffer buf;
    unsigned int index;
    unsigned int entries;
 };

like, that's literally it. three little members, one big job ✨

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💖 Members 💖

• buf — the standard struct ef4_buffer. nothing extra, nothing dramatic, just the classic.
• index — this is the buffer's index within the controller's buffer table 👑 (yes, the original really does have a lil typo there, we love that for us)
• entries — the number of buffer table entries. how many slots this bad boy is taking up.

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🦋 Description 🦋

ok so here's the lore 🌈 the NIC has a buffer table, right? and that table maps buffers of size EF4_BUF_SIZE. simple enough.

Event and descriptor rings get addressed through one or more buffer table entries — which means they can be physically non-contiguous, ngl. that's technically a thing that's possible! but bestie, we currently do not take advantage of that. like at all. it's giving "we could but we won't" 💀

here's where it gets hardware-dependent, and this is important so pay attention:

• On Falcon and Siena, we have to take care of allocating and initialising the entries ourselves. us. personally. 😭
• On later hardware, the firmware manages all of that, and index and entries are just... left as 0. sitting there. doing nothing. iconic of them honestly.

fr fr, remember which hardware you're on — the whole "who allocates the entries" situation flips depending on it 🙈

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🔥 SEE ALSO 🔥

Kernel file ./drivers/net/ethernet/sfc/falcon/net_driver.h, plus the whole squad of related structs and enums — go read them, they're all linked together iykyk:

• struct ef4_buffer(9)
• struct ef4_tx_buffer(9)
• struct ef4_tx_queue(9)
• struct ef4_rx_buffer(9)
• struct ef4_rx_page_state(9)
• struct ef4_rx_queue(9)
• struct ef4_channel(9)
• struct ef4_msi_context(9)
• struct ef4_channel_type(9)
• struct ef4_link_state(9)
• struct ef4_phy_operations(9)
• enum ef4_phy_mode(9)
• struct ef4_hw_stat_desc(9)
• struct ef4_nic(9)
• struct ef4_nic_type(9)

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and that's the whole page, bestie 💜 go forth and buffer-table responsibly ✨

this cutie lives at ./drivers/net/ethernet/sfc/falcon, dated October 2026 — and that's the struct ef4_special_buffer(9) sign-off, mwah 💋 🎀