This is a clone of issue RHEL-76802 to use for version rhel-9.6
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Original description:

Goal

When debugging storage related issues the reason for a I/O may contain important information leading to the root cause. QEMU itself reports the error reason but libvirt (and other management layers up the stack) don't have access to it. The error itself is thus deeply burried only in debug logs of libvirtd.

The goal of this issue is to improve the error propagation to upper layers so that the errors can be captured in more visible and easier to access logs.

Acceptance criteria

A list of verification conditions, successful functional tests, or expected outcomes in order to declare this story/task successfully completed.

• Allow users query reason for the I/O error
• Improve logging of I/O error reasons
• Improve notification of upper layers about I/O errors

The libvirt interface will consist of logging the I/O error reason in the VM log file as well as allowing clients to query it via the virDomainGetMessages() API. Any application listening to libvirt events will also receive a notification in the reason field of VIR_DOMAIN_EVENT_ID_IO_ERROR_REASON that a reason is available. Since the reason is not meant for machine consumption it needs to be queried extra.

Layered products above libvirt should register the VIR_DOMAIN_EVENT_ID_IO_ERROR_REASON event and also allow query the reason messages and log them for the users.

Easy way to test I/O errors with libvirt is to create a device-mapper device that will cause errors when interacted with:

1) create a image and map it to a loopback device

dd if=/dev/zero of=/tmp/img bs=512 count=1048576
losetup /dev/loop0 /tmp/img

2) create a device mapper device

dmsetup create errdev0 << EOF
0 261144 linear /dev/loop0 0
261144 5 error
261149 787427 linear /dev/loop0 261139
EOF

3) Use the device in a VM:

    <disk type='block' device='disk'>
      <driver name='qemu' type='raw'/>
      <source dev='/dev/mapper/errdev0'/>
      <target dev='vda' bus='virtio'/>
      <address type='pci' domain='0x0000' bus='0x00' slot='0x02' function='0x0'/>
    </disk>

4) In the VM read from the device

5) observe errors:

# virsh event --loop --all
 event 'io-error' for domain 'cd': /dev/mapper/errdev0 (virtio-disk0) report due to hypervisor-message

$ virsh dominfo cd
Id:             2
Name:           cd
UUID:           8e70100a-64b4-4186-aff9-e055c3075cb0
OS Type:        hvm
State:          running
CPU(s):         1
CPU time:       3032.4s
Max memory:     1024000 KiB
Used memory:    1024000 KiB
Persistent:     yes
Autostart:      disable
Managed save:   no
Security model: selinux
Security DOI:   0
Security label: unconfined_u:unconfined_r:svirt_t:s0:c429,c749 (permissive)
Messages:       tainted: hypervisor feature autodetection override
                tainted: custom device configuration
                I/O error: disk='vda', index='1', path='/dev/mapper/errdev0', timestamp='2025-01-28 15:47:52.776+0000', message'Input/output error'