STRUCT CMB(9)

💅 struct cmb(9) — from the Kernel API Manual ✨

okay bestie, so this one's a whole structural moment — we're talking about struct cmb, aka the basic channel measurement block, straight out of the Kernel API Manual. main character energy for your s390 measurement vibes 🎀

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🌸 NAME 🌸

struct cmb — the basic channel measurement block. that's it, that's the icon 💖

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✨ SYNOPSIS ✨

struct cmb {
    u16 ssch_rsch_count;
    u16 sample_count;
    u32 device_connect_time;
    u32 function_pending_time;
    u32 device_disconnect_time;
    u32 control_unit_queuing_time;
    u32 device_active_only_time;
    u32 reserved[2];
 };

lowkey a gorgeous little struct, no cap 🫶

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🦋 Members 🦋

here's the member-by-member breakdown, and yes we're doing all of them 💅

• ssch_rsch_count — the number of ssch and rsch. both of them. counted. iconic.
• sample_count — the number of samples. it's giving data collection 🍓
• device_connect_time — the time of device connect. clocked ⏰
• function_pending_time — the time of function pending. the waiting era 😭
• device_disconnect_time — the time of device disconnect. bye bestie 👋
• control_unit_queuing_time — the time of control unit queuing. the queue is queuing, fr fr
• device_active_only_time — the time of device active only. exactly what it says, and nothing else 💀
• reserved — unused in basic measurement mode. she's just sitting there, thriving, unbothered 🌈

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💜 Description 💜

so this is the measurement block as used by the hardware — like, the actual hardware's version, not a vibe we made up. 🌸 the fields get described further in z/Architecture Principles of Operation, chapter 17 — that's your required reading, iykyk 📚

now the important part, bestie, pay attention 🔥: the cmb area made up from these blocks must be a contiguous array and may not be reallocated or freed. like, do not touch. do not move. do not free. not me catching you trying to reallocate it 🙈

and also — only one cmb area can be present in the system. one. singular. she's the only one. periodt 👑

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🧚 SEE ALSO 🧚

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

a whole friend group, honestly 🫶 go read them all, slay ✨

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and that's the whole page, babes 💖 this little gem lives over in ./drivers/s390/cio and the docs are dated October 2026 — so consider yourself fully caught up in the future. mwah 💅🎀🦋