ccwchain_calc_length(9)

💅 ccwchain_calc_length(9) — the kernel API manual, bestie edition

okay so this is a page from the Kernel API Manual, section 9, and it's about ccwchain_calc_length — say that five times fast, i literally can't 😭 anyway it's lowkey a little function with big main character energy and we're gonna get into it.

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✨ NAME ✨

ccwchain_calc_length — calculate the length of the ccw chain. that's it. that's the whole job. she does one thing and she does it well 💅

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🎀 SYNOPSIS 🎀

int ccwchain_calc_length (u64 iova , struct channel_program *cp );

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🦋 ARGUMENTS 🦋

• iova — the guest physical address of the target ccw chain. like, which chain are we measuring, bestie? this is how you tell her 🫶
• cp — the channel_program on which to perform the operation. this is the poor little program getting the treatment.

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🌸 DESCRIPTION 🌸

so here's the vibe: this gives you the chain length, and it is not considering any TICs. none. zero. not even a little. 🙈

meaning? you've gotta do a whole new round for each TIC target. yes, each one. one round per target. it's giving "loop it yourself, queen." 🔥

and there's a lil bonus job on the side: the program also gets validated for the absence of any not-yet-supported indirect data addressing scenarios. so it's checking that you're not trying to pull anything the kernel doesn't support yet — no cap, it will notice 💀

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⭐ RETURN ⭐

the length of the ccw chain — or -errno, if things went sideways 😭

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👑 SEE ALSO 👑

• Kernel file ./drivers/s390/cio/vfio_ccw_cp.c
• cp_init(9)
• cp_free(9)
• cp_prefetch(9)
• cp_get_orb(9)
• cp_update_scsw(9)
• cp_iova_pinned(9)

like, go read the whole friend group, they literally all hang out in the same file 🧚

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fr fr: keep the TIC thing in mind or your chain length is gonna be lying to you 💖

okay that's the page!! this icon was living in ./drivers/s390/cio, stamped October 2026, and she ate. periodt. 🌈🎀✨