dm_consult_userspace(9)

💫 dm_consult_userspace(9) 💫

okay so bestie, welcome to the dm_consult_userspace page from the Kernel API Manual — like, this is the function that literally carries every single message between the kernel and the userspace log. bestie. the whole conversation. it's giving switchboard operator energy fr fr 🎀

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✨ NAME ✨

dm_consult_userspace — (the original NAME section is just the function name, no description, and honestly? she said "my name is enough" and left 💅)

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🦋 SYNOPSIS 🦋

int dm_consult_userspace (const char *uuid , uint64_t luid , int
       request_type , char *data , size_t data_size , char *rdata , size_t
       *rdata_size );

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🌸 ARGUMENTS 🌸

• uuid — the log's universal unique identifier. heads up bestie, it must be DM_UUID_LEN in size — no shrinkage, no vibes-based sizing, ok? 👑
• luid — the log's local unique identifier. a uint64_t, so she's got room 💜
• request_type — what kind of request this is. where do you find the valid ones? in include/linux/dm-log-userspace.h — go look, iykyk 🔥
• data — the data to tx to the server. yes "tx" as in transmit, we're being efficient today ⭐
• data_size — size of data, in bytes 📏
• rdata — the place to put the return data from the server. the reply slot 🫶
• rdata_size — a value-result situation: on the way in it's how much space you're giving, on the way out it's how much space got used. she does both, she's an icon 🎀

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💖 DESCRIPTION 💖

okay so first the spicy one: rdata_size is undefined on failure. like, don't go reading it after an error, she's not obligated to have anything sensible in there. 😭

second, and this is the cute part — the memory used to communicate with userspace is zero'ed before it gets populated. why? so that no unwanted bits leak from kernel space to user-space. a whole scrubbing ritual. ✨ we love a security-conscious queen ✨

and then the big flex: all userspace log communications between kernel and user space go through this function. every single one. main character energy, no cap 👑

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🔥 RETURN 🔥

• 0 on success — slay 🎉
• -EXXX on failure — some negative errno situation, read the code bestie 💀

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🧚 SEE ALSO 🧚

• Kernel file ./drivers/md/dm-log-userspace-transfer.c — go read the source, it ate 🌈

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lowkey reminder babes: uuid over here is a log's universal unique identifier, not a filesystem UUID, and it has to be exactly DM_UUID_LEN long or we're gonna have a bad time 🙈

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💅 that's the whole page! no notes, she's perfect 💅

and finally, the cute lil sign-off: this one lives in ./drivers/md, and the page is dated October 2026 — see you in the future bestie, mwah 🍓🦋✨