assign_domain_store(9)

💅 assign_domain_store — the kernel API manual, but make it make sense 🎀

okay bestie, so this page lives in the kernel API manual and it's all about assign_domain_store(9). Yes the name is a mouthful, no we are not skipping it. Buckle up 🦋

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✨ NAME ✨

assign_domain_store — parses the APQI from @buf and sets the corresponding bit in the mediated matrix device's AQM. That's it, that's the whole personality. 💅

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🫶 SYNOPSIS 🫶

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

literally just those four things coming at you. iconic signature tbh.

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🌸 ARGUMENTS 🌸

• dev — the matrix device. the main character of this whole operation 👑
• attr — the mediated matrix device's assign_domain attribute
• buf — a buffer containing the AP queue index (APQI) of the domain to be assigned. so like, the actual info you're handing over 🍓
• count — the number of bytes in buf

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💖 RETURN 💖

it returns the number of bytes processed if the APQI is valid ✨ otherwise it hands you back one of the following errors. no cap, that's the deal:

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🔥 DESCRIPTION 🔥

ngl this is where it gets spicy. here's your error lineup 🌈

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

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🧚 SEE ALSO 🧚

okay this list is LONG, but bestie I would never leave a single one out. every single one of these is real and here:

• Kernel file ./drivers/s390/crypto/vfio_ap_ops.c
• 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), assign_adapter_store(9), vfio_ap_mdev_unlink_adapter(9), unassign_adapter_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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kudos if you read every single one of those. genuinely obsessed with you 🫶

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and that's the whole page, bestie!! 🎀 it ships from ./drivers/s390/crypto, dated October 2026, and fr fr you just read the full assign_domain_store(9) manual page. slay. 💜✨