ENUM REQ_OP(9)

💅 enum req_op — the kernel API manual, but make it cute

okay so bestie, this is enum req_op from the Kernel API Manual, and it's literally the blueprint for "what kind of I/O are we even doing" in the block layer. 🎀

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✨ NAME ✨

enum req_op — Operations common to the bio and request structures. We use 8 bits for encoding the operation, and the remaining 24 for flags. no cap, that's the whole bit budget right there 💀

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🌸 SYNOPSIS 🌸

enum req_op {
    REQ_OP_READ ,
    REQ_OP_WRITE ,
    REQ_OP_FLUSH ,
    REQ_OP_DISCARD ,
    REQ_OP_SECURE_ERASE ,
    REQ_OP_ZONE_APPEND ,
    REQ_OP_WRITE_ZEROES ,
    REQ_OP_ZONE_OPEN ,
    REQ_OP_ZONE_CLOSE ,
    REQ_OP_ZONE_FINISH ,
    REQ_OP_ZONE_RESET ,
    REQ_OP_ZONE_RESET_ALL

};

like, twelve ops, all iconic, all in order, don't touch them 🙈

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🦋 Constants 🦋

• REQ_OP_READ — read sectors from the device 📖
• REQ_OP_WRITE — write sectors to the device ✍️
• REQ_OP_FLUSH — flush the volatile write cache 🚽 (ok not literally but the vibe is there)
• REQ_OP_DISCARD — discard sectors 🗑️
• REQ_OP_SECURE_ERASE — securely erase sectors 🔐
• REQ_OP_ZONE_APPEND — write data at the current zone write pointer 📍
• REQ_OP_WRITE_ZEROES — write the zero filled sector many times 0️⃣0️⃣0️⃣
• REQ_OP_ZONE_OPEN — Open a zone 🔓
• REQ_OP_ZONE_CLOSE — Close a zone 🔒
• REQ_OP_ZONE_FINISH — Transition a zone to full 🈵
• REQ_OP_ZONE_RESET — reset a zone write pointer 🔄
• REQ_OP_ZONE_RESET_ALL — reset all the zone present on the device 🌪️

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💜 Description 💜

so the least significant bit of the operation number is basically the main character here — it tells you which way the data is flowing, iykyk:

• if the least significant bit is set, transfers are TO the device 📥
• if the least significant bit is not set, transfers are FROM the device 📤

and if an operation does not transfer data? then the least significant bit has no meaning. it's just there, vibing, contributing nothing. we've all been there tbh 💀

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🔥 SEE ALSO 🔥

• Kernel file ./include/linux/blk_types.h
• blk_path_error(9)

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fr fr, the whole thing lives under ./include/linux, dated October 2026, and this page is enum req_op(9). slay, go read blk_types.h bestie 🫶✨💖