On 6/10/25 19:15, Simon Coter wrote:
> Adding users DL to possibly reach out a wider audience.
>
> Simon
>
Dropping devel list as this is users list material.
>> On Jun 9, 2025, at 7:28 PM, Annie Li <annie...@oracle.com> wrote:
>>
>> Hello,
>>
>> I've been looking at source code related to persistent reservation and
>> got confused a little bit about managed persistent reservation disks.
>> For disk configured with 'managed=yes' as the following,
>>
>> <reservations managed='yes'>
>> <source type='unix' path='/var/lib/libvirt/qemu/domain-7-
>> brml10g19-iscsi-rese/pr-helper0.sock' mode='client'/>
>> </reservations>
>>
>> libvirt is responsible for starting a pr-helper program with a
>> specific associated socket file. The following source code shows that
>> there is only one pr-helper and socket file associated with the
>> managed disks for one VM.
>>
>> const char *
>> qemuDomainGetManagedPRAlias(void)
>> {
>> return "pr-helper0";
>> }
>> char *
>> qemuDomainGetManagedPRSocketPath(qemuDomainObjPrivate *priv)
>> {
>> return g_strdup_printf("%s/%s.sock", priv->libDir,
>> qemuDomainGetManagedPRAlias());
>> }
>>
>> So if the VM is booted with multiple disks configured with
>> 'managed=yes' for reservation, I suppose these multiple disks share
>> the this managed pr-helper and socket file. However, per the qemu
>> document, https://www.qemu.org/docs/master/interop/pr-helper.html
>> <https://www.qemu.org/docs/master/interop/pr-helper.html>
>> "It is invalid to send multiple commands concurrently on the same
>> socket. It is however possible to connect multiple sockets to the
>> helper and send multiple commands to the helper for one or more file
>> descriptors."
>>
This certainly did not use to be the case. IIRC this was discussed in
this very old thread:
https://lists.libvirt.org/archives/list/de...@lists.libvirt.org/thread/UUL3B7ZLAW4WPVUBX2R76GZTOS24Z2SD/
Maybe QEMU has some internal lock that does the right thing and
serializes requests?
Michal
>> Due to this limitation above, only one persistent reservation disk is
>> allowed as managed in theory. However, libvirt doesn't throw out any
>> error or warning when the VM is booted up with multiple managed
>> persistent reservation disks. I am wondering if I've missed something
>> here?
>>
>> For unmanaged persistent reservation disks, libvirt doesn't start the
>> pr-helper program for them. It is user's responsibility to start this
>> program with customized socket file per disk, but the complexity
>> increases with numbers of persistent reservation disks, especially in
>> the case of hotplug/hotunplog. Is there any plan to support multiple
>> managed persistent reservation disks with separate pr-helper/socket file?
>>
>> Any suggestions/clarifications are greatly appreciated.
>>
>> Thanks
>>
>> Annie
>>
>
