DEFINE_FLEX(9)

💅 DEFINE_FLEX(9) — the Kernel API Manual one, bestie

okay so real talk, this is DEFINE_FLEX from section 9 of the kernel API manual, and honestly? it's giving "make me a struct on the stack with a flexible array at the end and zero it out for me" ✨ and we're gonna learn it together 🫶

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✨ NAME ✨

DEFINE_FLEX — define an on-stack instance of structure with a trailing flexible array member. literally that's the whole vibe 💖

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🌸 SYNOPSIS 🌸

DEFINE_FLEX (TYPE , NAME , MEMBER , COUNTER , COUNT );

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🎀 ARGUMENTS 🎀

• TYPE — the structure type name, and yes bestie, that includes the "struct" keyword, don't forget it 🙈
• NAME — the name for the variable you're defining 🏷️
• MEMBER — the name of the array member 👑
• COUNTER — the name of the __counted_by member 🔢
• COUNT — how many elements are in the array; it must be compile-time const, no cap, this one's strict 💀

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🦋 DESCRIPTION 🦋

So it defines a zeroed, on-stack instance of your TYPE structure, with a trailing flexible array member 🌈 — the whole thing just appears, zeroed and ready, main character energy fr fr.

Then when you wanna know stuff about it, the tooling is right there:

• use __struct_size(NAME) to get the compile-time size of it afterwards 💜
• use __member_size(NAME->member) to get the compile-time size of NAME members ⭐
• use STACK_FLEX_ARRAY_SIZE(name, member) to get the compile-time number of elements in the array member 🍓

it's iconic, it's convenient, it's on the stack, periodt 👑

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🔥 SEE ALSO 🔥

the kernel file ./include/linux/overflow.h — and omg the friend group is HUGE, ok here we go, every single one of them:

check_add_overflow(9), wrapping_add(9), wrapping_assign_add(9), check_sub_overflow(9), wrapping_sub(9), wrapping_assign_sub(9), check_mul_overflow(9), wrapping_mul(9), check_shl_overflow(9), overflows_type(9), range_overflows(9), range_overflows_t(9), range_end_overflows(9), range_end_overflows_t(9), castable_to_type(9), size_mul(9), size_add(9), size_sub(9), array_size(9), array3_size(9), flex_array_size(9), struct_size(9), struct_size_t(9), struct_offset(9), __DEFINE_FLEX(9), _DEFINE_FLEX(9), DEFINE_RAW_FLEX(9), STACK_FLEX_ARRAY_SIZE(9), typeof_flex_counter(9), overflows_flex_counter_type(9), __set_flex_counter(9)

like damn, that's a whole group chat 💀💖

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and that's the page, bestie 🧚 this came from ./include/linux and the lovely Kernel API Manual, dated October 2026 — catch you on the next one, mwah 💅💜