ccw_device_start_key(9)

💅 ccw_device_start_key — like, the key-flavored version of starting an s390 channel program

okay so bestie, welcome to the Kernel API Manual entry for ccw_device_start_key. yes it's a section 9 page, yes it's about mainframe I/O, and yes it's iconic. buckle up. 🎀

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✨ NAME ✨

ccw_device_start_key — start a s390 channel program with key 🔑

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✨ SYNOPSIS ✨

int ccw_device_start_key (struct ccw_device *cdev , struct ccw1 *cpa ,
unsigned long intparm , __u8 lpm , __u8 key , unsigned long flags );

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✨ ARGUMENTS ✨

• cdev — the target ccw device. like, the device we're doing the thing to 🫶
• cpa — logical start address of the channel program. the address, bestie ✨
• intparm — a user specific interruption parameter. it gets presented back to cdev's interrupt handler, which lets a device driver associate that interrupt with one particular I/O request. it's giving "remember me" energy 💖
• lpm — defines the channel path to be used for a specific I/O request. and heads up: a value of 0 will make cio use the opm 👀
• key — the storage key to be used for the I/O 🔑
• flags — additional flags; defines the action to be performed for I/O processing 🚩

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✨ DESCRIPTION ✨

So you're starting a S/390 channel program. slay. 🎉

When the interrupt arrives, the IRQ handler is called — and the timing is very main character, because it can be:

• immediately
• delayed (dev-end missing, or sense required) 😭
• never (no IRQ handler registered) 💀

The interruption handler will echo back the intparm you specified here — unless another interruption parameter gets specified by a subsequent invocation of ccw_device_halt or ccw_device_clear. so like, don't count on it if someone else on the chat is also passing notes 🙈

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✨ RETURN ✨

• 0 — if the operation was successful ✨
• -EBUSY — if the device is busy, or status pending 😤
• -EACCES — if no path specified in lpm is operational 🚫
• -ENODEV — if the device is not operational 💀

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✨ CONTEXT ✨

Interrupts disabled, ccw device lock held. fr fr, you gotta be holding that lock. no cap. 🔒

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✨ SEE ALSO ✨

The kernel file ./drivers/s390/cio/device_ops.c — that's literally where this lives 🗂️

and then the whole friend group, all of them, not skipping a single one 👑

• ccw_device_set_options_mask(9) — ccw_device_set_options(9) — ccw_device_clear_options(9) — ccw_device_is_pathgroup(9) — ccw_device_is_multipath(9) — ccw_device_clear(9) — ccw_device_start_timeout_key(9) — ccw_device_start(9) — ccw_device_start_timeout(9) — ccw_device_halt(9) — ccw_device_resume(9) — ccw_device_get_ciw(9) — ccw_device_get_path_mask(9) — ccw_device_get_chp_desc(9) — ccw_device_get_util_str(9) — ccw_device_get_id(9) — ccw_device_tm_start_timeout_key(9) — ccw_device_tm_start_key(9) — ccw_device_tm_start(9) — ccw_device_tm_start_timeout(9) — ccw_device_get_mdc(9) — ccw_device_tm_intrg(9) — ccw_device_get_schid(9) — ccw_device_pnso(9) — ccw_device_get_cssid(9) — ccw_device_get_iid(9) — ccw_device_get_chpid(9) — ccw_device_get_chid(9)

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that's the whole page bestie, go start some channel programs responsibly 💜

— source/version: ./drivers/s390/cio, dated October 2026 — mwah, xoxo, the Kernel API Manual 🧚‍♀️