Re: [Qemu-devel] qemu-nbd daemonizing?

[Paolo Bonzini <pbonzini@redhat.com>]

On 01/15/2012 01:59 PM, Michael Tokarev wrote:
> On 15.01.2012 14:51, Paolo Bonzini wrote:
>> On 01/14/2012 10:26 AM, Michael Tokarev wrote:
>>> After looking at the yesterdays issue with non-absolute
>>> paths for qemu-nbd arguments and daemon(3), I've a
>>> question.
>>>
>>> Why qemu-nbd daemonizes, and does that only when device
>>> argument is given (dropping -v/verbose case for now)?
>>>
>>> This raises two questions:
>>>
>>>    - shouldn't it do the same daemonizing in case of usual
>>>      tcp export?
>>
>> Perhaps yes, but in that case you cannot use "qemu-nbd -d" to
>> kill the daemonized process.
>
> Sorry?  qemu-nbd -d will connect to the socket the daemonized
> daemon is listening on, the same way as it is done now --
> nothing really changes there.

No, "qemu-nbd -d" will connect to the /dev/nbdX device and tell the 
kernel to disconnect.  This will terminate the daemon (as long as you 
didn't use --persistent, at least).

>> Also, one of the best things of systemd is that it handles
>> daemonization on its own, so nowadays it is better not to
>> have process send themselves into background by default.
>
> First, not all the world is systemd.  Second, my question was
> merely about consistency -- -c does daemonizing currently and
> there's no way to stop it from doing so

--verbose is a counterintuitive way not to daemonize, but it works.

> The primary question was why -c daemonizes unconditionally.

I don't know.  But I don't think daemonizing is really a feature, just 
something historical that we have to deal with.

> qemu-nbd was runnable on win32 before, so historically it
> was exactly the opposite.   I asked you because you mentioned
> it is linux-only for the first time, but indeed, at that
> time it wasn't compilable on win32 already.

Fixing it would be good indeed.  We can use qemu-thread for that for 
example.  But it looks like the third commit ever to qemu-nbd.c already 
made it non-Linux-only.  I don't think there ever was a release that 
supported qemu-nbd on Win32, right?

Paolo