[SRU][P][PATCH 0/1] Documentation update for [Ubuntu25.04] "virsh attach-interface" requires a reboot to reflect the attached interfaces on the guest (LP: #2111231)

[Massimiliano Pellizzer]

BugLink: https://bugs.launchpad.net/bugs/2111231

[ Impact ]

powerpc/pseries/dlpar: Search DRC index from ibm,drc-indexes for IO add

IO hotplug add event is handled in the user space with drmgr tool.
After the device is enabled, the user space uses /sys/kernel/dlpar
interface with “dt add index <drc_index>” to update the device tree.
The kernel interface (dlpar_hp_dt_add()) finds the parent node for
the specified ‘drc_index’ from ibm,drc-info property. The recent FW
provides this property from 2017 onwards. But KVM guest code in
some releases is still using the older SLOF firmware which has
ibm,drc-indexes property instead of ibm,drc-info.

If the ibm,drc-info is not available, this patch adds changes to
search ‘drc_index’ from the indexes array in ibm,drc-indexes
property to support old FW.

[ Fix ]

Backport from linux-next commit:
- 41a1452759a8b1 powerpc/pseries/dlpar: Search DRC index from ibm,drc-indexes for IO add

[ Test Plan ]

Perform a virsh attach-device on an L2 VM (on a Power instance)
and verify that the corresponding hotplug operation does go through.

[ Regression Potential ]

The patch introduces a fallback mechanism that scans ibm,drc-indexes
only when ibm,drc-info is missing, minimizing disruption to existing behavior.
However, in malformed or ambiguous device trees,
the fallback logic might match unintended nodes,
potentially misconfiguring the hotplug target.