Re: [Qemu-block] interactive qemu-img

[Nir Soffer]

On Mon, Jul 30, 2018 at 11:09 PM Eric Blake <address@hidden> wrote:

On 07/30/2018 02:54 PM, Nir Soffer wrote:

>>> $ qemu-img
>>> qemu-img: Not enough arguments
>>> Try 'qemu-img --help' for more information
>
>
> This is not user friendly, but unfortunately very common.
> It can be improved by treating no arguments as --help, like git.

I somewhat disagree that git is a good example.  If '--help' occupies
more than about 25 lines (a screenful on some default terminal sizes),
the mere fact that you have to scroll to read it makes it less helpful
than a 2-liner statement that lets you know "I couldn't do anything
useful with your botched command line, please read the documentation and
try again".  'git' behaving as 'git --help' outputs 42 lines, which
fails my 'one screenful' test; and 'qemu-img --help' at 104 lines is
definitely too verbose to be the default behavior when --help is not given.

/me Wow - I can't believe I'm actually about to use this as an example, but:

'cvs' and 'cvs --help' is just 13 lines (except to stderr, when it
should have been stdout), and gives enough hints on how to get more
specific help on a particular topic.  Great for the plain 'cvs' case; a
bit more debatable on 'cvs --help' (the fact that you have to ask for
help twice: once for the summary, again for the specific help, gets
tedious).

At any rate, getting command-line tools to have user-friendly behavior
when insufficient arguments are supplied is an artform, and you'll find
lots of bikeshed colors out there.

And regardless of any opinions I've expressed above, this thread does
point out that 104 lines for 'qemu-img --help' is long, and anything we
can do to make that easier to digest may still be worthwhile.

I agree that git help is too long, and falling back to --help without improving

qemu-img help is not very useful.

What we need is something like:

$ qemu-img 

Commands:

  amend       description...

  bench       description...

  check       description...

  commit      description...

  compare     description...

  convert     description...

  create      description...

  dd          description...

  info        description...

  map         description...

  measure     description...

  snapshot    description...

  rebase      description...

  resize      description...

  

This fits in a terminal, and we have space for additional tips or common

command line options.

Note that this is not "botched command line", so we don't need to complain

about missing arguments.

    qemu-img create --help

Should show only help for create.

virsh works in a similar way, but it has too many commands in the main help.

Of course this may break some management systems calling qemu-img --help
and parsing the output. We used to do this in oVirt in the past :-)

Nir