[Qemu-devel] Writing a C library to generate qemu command lines and configuration files

["Richard W.M. Jones" <rjones@redhat.com>]

Firstly, is there such a thing already?  (libvirt doesn't count since
it cannot generate -readconfig configuration files)

Well, I have written one.  It's in C and doesn't have any dependencies
beyond the standard C library:

  https://github.com/rwmjones/libguestfs/tree/max-disks/common/qemuopts

It models command line parameters as either flags (eg. ‘-nodefconfig’),
flags with a single argument (‘-name guest’), or flags taking a list
(eg. ‘-drive file=foo,id=bar’ modeled as a list of strings).

I'm immediately aware that there are shortcomings with this approach
(see below).  Is there a better model to use for qemu command line
options that also allows -readconfig config files to be generated?

Some of the more obvious problems:

* I don't know if single flags can be translated into config files.

* Config files treat the "id=.." parameter as special, eg:
  ‘-drive file=foo,id=bar’ is translated to:

  [drive "bar"]
    file = "foo"

* There's no clear mapping between some command line parameters and
  the config file, eg. ‘-m 2048 -kernel foo’ should be translated into:

  [memory]
    size = "2048"
  [machine]
    kernel = "foo"

  but my library couldn't do that translation without a look-up table
  that would duplicate the internals of qemu.

There are also unknown unknowns:

* Is comma-quoting (ie. doubling any commas) sufficient?  Or are there
  other forms of quoting?  A quick look at options parsing in qemu
  doesn't show any.

* From the point of view of a client generating command lines, is there
  any significance to dotted names (eg. ‘-drive file.driver=ssh,...’)

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
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