handle_mailb...md_from_user(9)

✨ handle_mailb...md_from_user(9) ✨

okay so this is a page from the Kernel API Manual, bestie — it's literally called handle_mailb...md_from_user(9) and it's all about how the kernel handles a mailbox command that came from userspace. the way that the kernel just... does that. 💅

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🎀 NAME 🎀

handle_mailbox_cmd_from_user — Dispatch a mailbox command for userspace.

like, it's giving "middle management for mailbox commands" and honestly? iconic. 👑

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🦋 SYNOPSIS 🦋

int handle_mailbox_cmd_from_user (struct cxl_mailbox *cxl_mbox , struct
cxl_mbox_cmd *mbox_cmd , u64 out_payload , s32 *size_out , u32 *retval
);

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🌸 ARGUMENTS 🌸

• cxl_mbox — The mailbox context for the operation. it's the whole vibe of the mailbox, yk?
• mbox_cmd — The validated mailbox command. key word: validated. somebody already did the vibe check on this one. ✅
• out_payload — Pointer to userspace's output payload.
• size_out — (Input) Max payload size to copy out. (Output) Payload size hardware generated. so it goes in as a limit and comes out as a real number — main character energy honestly. 💫
• retval — Hardware generated return code from the operation.

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💖 RETURN 💖

• 0 — Mailbox transaction succeeded. This implies the mailbox protocol completed successfully not that the operation itself was successful. no cap, read that twice — the transaction slayed, doesn't mean the actual operation ate. 😭
• -ENOMEM — Couldn't allocate a bounce buffer.
• -EFAULT — Something happened with copy_to/from_user.
• -EINTR — Mailbox acquisition interrupted.
• -EXXX — Transaction level failures.

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🔥 DESCRIPTION 🔥

Dispatches a mailbox command on behalf of a userspace request. The output payload is copied to userspace.

See cxl_send_cmd.

fr fr that's it — it's a dispatch girlie. it takes the request, sends it off, and copies the output payload back to userspace. 🫶

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🌈 SEE ALSO 🌈

Kernel file ./drivers/cxl/core/mbox.c and friends, bestie:

• cxl mbox(9)
• cxl_internal_send_cmd(9)
• cxl_payload_from_user_allowed(9)
• cxl_validate_cmd_from_user(9)
• cxl_walk_cel(9)
• cxl_enumerate_cmds(9)
• cxl_mem_get_event_records(9)
• cxl_mem_get_partition_info(9)
• cxl_dev_state_identify(9)
• cxl_mem_sanitize(9)

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⭐ that's the whole page, no secrets, no hidden options. go read the SEE ALSO list, it's lowkey a whole friend group. 🙈

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🧚 and that's the tea! this one lives in ./drivers/cxl/core, it's dated October 2026, and it's filed under handle_mailb...md_from_user(9) — so you always know where to find it again. mwah! 💜