Re: [PATCH 1/3] qsd: Add pre-init argument parsing pass

[Markus Armbruster]

Hanna Reitz <hreitz@redhat.com> writes:

> On 20.01.22 17:00, Markus Armbruster wrote:
>> Kevin Wolf <kwolf@redhat.com> writes:
>>
>>> Am 19.01.2022 um 14:44 hat Hanna Reitz geschrieben:
>>>> On 19.01.22 13:58, Markus Armbruster wrote:
>>>>> Hanna Reitz <hreitz@redhat.com> writes:
>>>>>
>>>>>> We want to add a --daemonize argument to QSD's command line.
>>>>> Why?
>>>> OK, s/we/I/.  I find it useful, because without such an option, I need to
>>>> have whoever invokes QSD loop until the PID file exists, before I can be
>>>> sure that all exports are set up.  I make use of it in the test cases added
>>>> in patch 3.
>>>>
>>>> I suppose this could be worked around with a special character device, like
>>>> so:
>>>>
>>>> ```
>>>> ncat --listen -U /tmp/qsd-done.sock </dev/null &
>>>> ncat_pid=$!
>>>>
>>>> qemu-storage-daemon \
>>>>      ... \
>>>>      --chardev socket,id=signal_done,path=/tmp/qsd-done.sock \
>>>>      --monitor signal_done \
>>>>      --pidfile /tmp/qsd.pid &
>>>>
>>>> wait $ncat_pid
>>>> ```
>>>>
>>>> But having to use an extra tool for this is unergonomic.  I mean, if 
>>>> there’s
>>>> no other way...
>>
>> I know duplicating this into every program that could server as a daemon
>> is the Unix tradition.  Doesn't make it good.  Systemd[*] has tried to
>> make it superfluous.
>
> Well.  I have absolutely nothing against systemd.  Still, I will not
> use it in an iotest, that’s for sure.

My point isn't "use systemd in iotests".  It's "consider doing it like
systemd", i.e. do the daemonization work in a utility program.  For what
it's worth, Linux has daemonize(1).

[...]

>> Care to put a brief version of the rationale for --daemonize and for
>> forking early in the commit message?
>
> Well, my rationale for adding the feature doesn’t really extend beyond
> “I want it, I find it useful, and so I assume others will, too”.

Don't pretend to be obtuse, it's not credible :)  You mentioned iotests,
which makes me guess your rationale is "I want this for iotests, and
there may well be other uses."

> I don’t really like putting “qemu-nbd has it” there, because... it was
> again me who implemented it for qemu-nbd.  Because I found it useful.  
> But I can of course do that, if it counts as a reason.

Useful *what for*, and we have rationale.

> I can certainly (and understand the need to, and will) elaborate on
> the “This will require forking the process before we do any complex 
> initialization steps” part.

Thanks!