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


From: Paolo Bonzini
Subject: Re: [Qemu-devel] qemu-nbd daemonizing?
Date: Sun, 15 Jan 2012 17:17:02 +0100
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:9.0) Gecko/20111222 Thunderbird/9.0

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



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