assign_adapter_store(9)

💖 assign_adapter_store(9) 💖

okay so real talk, this is from the Kernel API Manual and it's the page for assign_adapter_store — she's the one who parses the APID out of @buf and sets the matching bit in the mediated matrix device's APM. iconic behavior tbh 🎀

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✨ SYNOPSIS ✨

ssize_t assign_adapter_store (struct device *dev , struct
device_attribute *attr , const char *buf , size_t count );

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🫶 ARGUMENTS 🫶

• dev — the matrix device, bestie. main character.
• attr — the mediated matrix device's assign_adapter attribute. she's the vibe.
• buf — a buffer holding the AP adapter number (APID) that's getting assigned 💅
• count — the number of bytes in buf (yes, literally just the byte count, ngl)

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🔥 RETURN 🔥

if the APID is valid you get the number of bytes processed — slay ✨. otherwise? one of the following errors gets thrown at you:

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🌸 DESCRIPTION 🌸

here's your error lineup, numbered and everything, no cap:

1. -EINVAL — the APID is not a valid number 🙈
2. -ENODEV — the APID exceeds the maximum value configured for the system 💀
3. -EADDRNOTAVAIL — an APQN derived from the cross product of the APID being assigned and the APQIs previously assigned is not bound to the vfio_ap device driver; or, if no APQIs have yet been assigned, the APID is not contained in an APQN bound to the vfio_ap device driver 😭
4. -EADDRINUSE — an APQN derived from the cross product of the APID being assigned and the APQIs previously assigned is being used by another mediated matrix device 🫠
5. -EAGAIN — a lock required to validate the mdev's AP configuration could not be obtained 💀

lowkey listen: those cross-product APQN checks are doing a LOT of heavy lifting, so don't be surprised when -EADDRNOTAVAIL or -EADDRINUSE shows up. read the number, read the reason, periodt.

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🦋 SEE ALSO 🦋

kernel file: ./drivers/s390/crypto/vfio_ap_ops.c 👑

and the whole friend group:

get_update_locks_for_kvm(9), release_update_locks_for_kvm(9), get_update_locks_for_mdev(9), release_update_locks_for_mdev(9), get_update_locks_by_apqn(9), get_update_locks_for_queue(9), vfio_ap_mdev_get_queue(9), vfio_ap_wait_for_irqclear(9), vfio_ap_free_aqic_resources(9), vfio_ap_irq_disable(9), vfio_ap_validate_nib(9), ensure_nib_shared(9), vfio_ap_irq_enable(9), vfio_ap_le_guid_to_be_uuid(9), handle_pqap(9), vfio_ap_mdev_verify_no_sharing(9), vfio_ap_mdev_validate_masks(9), vfio_ap_mdev_unlink_adapter(9), unassign_adapter_store(9), assign_domain_store(9), unassign_domain_store(9), assign_control_domain_store(9), unassign_control_domain_store(9), vfio_ap_mdev_set_kvm(9), vfio_ap_mdev_unset_kvm(9), vfio_ap_mdev_resource_in_use(9), vfio_ap_mdev_hot_unplug_cfg(9), vfio_ap_mdev_cfg_remove(9), vfio_ap_mdev_on_cfg_remove(9), vfio_ap_filter_apid_by_qtype(9), vfio_ap_mdev_cfg_add(9), vfio_ap_mdev_on_cfg_add(9), vfio_ap_on_cfg_changed(9)

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okay that's the whole page, go read it and get your APID assigned bestie 🌈💜

sign-off time: this cutie lives in ./drivers/s390/crypto and the page is dated October 2026 — mwah, assign_adapter_store(9) out 💅✨🎀