Re: [Qemu-block] [Qemu-devel] [PATCH 4/4] scsi: add persistent reservation manager using qemu-pr-helper

[Paolo Bonzini]

On 19/09/2017 15:23, Paolo Bonzini wrote:
> On 19/09/2017 15:12, Daniel P. Berrange wrote:
>> On Tue, Sep 19, 2017 at 02:57:00PM +0200, Paolo Bonzini wrote:
>>> On 19/09/2017 14:53, Daniel P. Berrange wrote:
>>>>> +    /* Try to reconnect while sending the CDB.  */
>>>>> +    for (attempts = 0; attempts < PR_MAX_RECONNECT_ATTEMPTS; attempts++) 
>>>>> {
>>>>
>>>> I'm curious why you need to loop here. The helper daemon should be running
>>>> already, as you're not spawning it on demand IIUC. So it shoudl either
>>>> succeed first time, or fail every time.
>>>
>>> You're focusing on the usecase where the helper daemon is spawned per-VM
>>> by the system libvirtd, which I agree is the most important one.
>>> However, the other usecase is the one with a global daemon, access to
>>> which is controlled via Unix permissions.  This is not SELinux-friendly,
>>> but it is nicer for testing and it is also the only possibility for user
>>> libvirtd.
>>>
>>> In that case, upgrading QEMU on the host could result in a "systemctl
>>> restart qemu-pr-helper.service" (or, hopefully unlikely, a crash could
>>> result in systemd respawning the daemon).  Reconnect is useful in that case.
>>
>> If using systemd socket activation and you restart the daemon, the listening
>> socket should be preserved, so you shouldn't need to reconnect - the client
>> should get queued until it has started again (likewise on crash).
> 
> Oh, that's cool.  I didn't know that.

... wait, I do need to reconnect, because the active socket is closed.
I only don't need to retry and wait between the retries.

Paolo