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Re: [PATCH 1/2] trace: document how to specify multiple --trace patterns

From: John Snow
Subject: Re: [PATCH 1/2] trace: document how to specify multiple --trace patterns
Date: Wed, 13 Jan 2021 18:08:53 -0500
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 1/13/21 5:15 PM, Eric Blake wrote:
On 1/13/21 3:42 PM, John Snow wrote:
On 1/13/21 4:48 AM, Stefan Hajnoczi wrote:
QEMU options are single dash with double dash accepted for
compatibility but
help and other docs have single dash so these (and below) should be
(Also a bit less typing for otherwise already way too long command
Is this documented somewhere?

I was under the impression that '-' is legacy syntax and '--' is the
preferred syntax. There are examples of '--' on the QEMU man page.

Historically, uses of 'getopt_long()' support only double dash, while
'getopt_long_only()' support both single and double.  While qemu does
not use getopt_long_only() (because it rolls its own parser instead), it
certainly tries to behave as if it does.  Meanwhile, our other tools
like qemu-img or qemu-storage-daemon use getopt_long().  I'm in favor of
preferring the double-dash in documentation, even when single-dash
works, especially for any option (like --trace) that is used for more
tools than just qemu proper, because it makes for easier copy-paste
between options that work for all tools in the qemu suite rather than
just qemu.

Yes, this makes sense.

Let's reach agreement, document it, and then make the documentation


My naive impression was that double-dash is the preferred idiom in
linuxdom in general for any multi-character option.

We might hang on to single-dash for backwards compatibility, but I doubt
we want to enshrine that as our preferred way.

Is there a reasoning I am unaware of?

Continuing to document '-machine' instead of '--machine' for qemu is
debatable because we don't support 'qemu-img --machine' or
'qemu-storage-daemon --machine'; but since 'qemu-img -trace' is an error
while 'qemu-img --trace' works, I'm definitely in favor of preferring
'--trace' everywhere in our docs.

At that point, it's a guessing game as to which binaries support which flags and using which spellings -- maybe some will pick up new flags later and so on.

Skip the fuss and just insist on the double dash, I think.


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