enable_cmf(9)

💅 enable_cmf — bestie, we're turning the measurement ON

okay so real talk, this page is from the Kernel API Manual (yes, the 9 section, kernel-space girlies only ✨) and it's called enable_cmf, which is basically "channel measurement" but make it a function. let's get into it 🎀

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🌸 NAME 🌸

enable_cmf — switch on the channel measurement for a specific device 💫

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✨ SYNOPSIS ✨

int enable_cmf (struct ccw_device *cdev );

one function, one argument, and it returns an int. she's simple, she's iconic 👑

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🦋 ARGUMENTS 🦋

• cdev — the ccw device you wanna enable. like, the specific device. the main character of this whole operation 🫶

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💖 DESCRIPTION 💖

so what she does is: enable channel measurements for cdev. that's it, that's the vibe ✨

but here's the plot twist, bestie — if you call this on a device where channel measurement is already enabled, it triggers a reset of the measurement data. no cap. so it's not a no-op, it's a glow-up-with-amnesia situation 💀

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🔥 RETURN 🔥

• 0 for success 🎉
• or a negative error value 😭 (yes, negative. read the number, bestie, don't just check for truthiness)

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⭐ CONTEXT ⭐

non-atomic — so she is not atomic, okay? she's not out here being all indivisible and untouchable. plan accordingly 💅

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🌈 SEE ALSO 🌈

the whole friend group, fr fr:

• Kernel file ./drivers/s390/cio/cmf.c
• enum cmb_format(9)
• struct cmb_operations(9)
• struct cmb_area(9)
• struct cmb(9)
• struct cmbe(9)
• __disable_cmf(9)
• disable_cmf(9)
• cmf_read(9)
• cmf_readall(9)
• cmf_reactivate(9)

they're all in the ./drivers/s390/cio clique, iykyk 🧚

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and that's the whole page, babe — sourced straight from ./drivers/s390/cio, stamped October 2026, no notes. go enable some measurements, you got this 🍓💜