kvm_stats_read(9)

✨ NAME ✨

kvm_stats_read — the common function to read from the binary statistics file descriptor 💖 (and yes bestie, this is a section 9 Kernel API Manual moment, we're in kernel developer territory, act accordingly 💅)

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🎀 SYNOPSIS 🎀

ssize_t kvm_stats_read (char *id , const struct kvm_stats_header *header
, const struct kvm_stats_desc *desc , void *stats , size_t size_stats ,
char __user *user_buffer , size_t size , loff_t *offset );

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🌸 ARGUMENTS 🌸

• id — the identification string of the stats 🏷️ like, its little name tag
• header — the stats header, for a vm or a vcpu (both welcome here 🫶)
• desc — start address of an array of stats descriptors, again for a vm or a vcpu
• stats — start address of the stats data block for a vm or a vcpu
• size_stats — the size of the stats data block that stats points at 📏
• user_buffer — start address of the userspace buffer (where the good stuff lands 🎁)
• size — the requested read size, coming from userspace
• offset — the start position that the content gets read from, for the corresponding vm or vcpu file descriptor 📍

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🦋 DESCRIPTION 🦋

okay so the file content of a vm/vcpu file descriptor is now defined like this, no cap 👇

┌─────────────┐
│ Header      │
│ id string   │
│ Descriptors │
│ Stats Data  │
└─────────────┘

so like, this function technically lets userspace read any amount of data (as long as it's in the limit ✋) from any position, but the typical usage? it's giving a whole little ritual. here's the steps everyone actually follows:

1. Read the header from offset 0. Grab the offset of the descriptors and the stats data, plus some other necessary information. This is a one-time work for the lifecycle of the corresponding vm/vcpu stats fd ✨
2. Read the id string from its offset. Also a one-time work for the lifecycle of the corresponding vm/vcpu stats fd 🎀
3. Read the descriptors from their offset and discover all the stats by parsing the descriptors. Yep — one-time work for the lifecycle of the corresponding vm/vcpu stats fd 💫
4. Periodically read the stats data from its offset using pread 🔁 (this is the part where you just keep coming back, main character energy)

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💫 RETURN 💫

the number of bytes that has been successfully read 📊 slay.

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🌈 SEE ALSO 🌈

Kernel file ./virt/kvm/binary_stats.c 👀 go read it, iykyk

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kay so that's the whole page, bestie — brought to you from ./virt/kvm, dated October 2026, and it's literally kvm_stats_read(9) fr fr. mwah 💋💖✨