Re: [PATCH] softmmu/vl.c: Handle '-cpu help' and '-device help' before 'no default machine'

[Kashyap Chamarthy <kchamart@redhat.com>]

[Cc: Markus; he'd be pleasantly surprised with this, if he already
hadn't noticed this, as he was also mildly annoyed about this the other
day.]

On Fri, Mar 13, 2020 at 05:24:47PM +0000, Peter Maydell wrote:
> Currently if you try to ask for the list of CPUs for a target
> architecture which does not specify a default machine type
> you just get an error:
> 
>   $ qemu-system-arm -cpu help
>   qemu-system-arm: No machine specified, and there is no default
>   Use -machine help to list supported machines

I just applied the patch and built on QEMU.

With `qemu-system-arm`:

    $> ./arm-softmmu/qemu-system-arm -cpu help | head -5
    Available CPUs:
      arm1026
      arm1136
      arm1136-r2
      arm1176

    $> ./arm-softmmu/qemu-system-arm -device help | head -5
    Controller/Bridge/Hub devices:
    name "i82801b11-bridge", bus PCI
    name "ioh3420", bus PCI, desc "Intel IOH device id 3420 PCIE Root Port"
    name "pci-bridge", bus PCI, desc "Standard PCI Bridge"
    name "pci-bridge-seat", bus PCI, desc "Standard PCI Bridge (multiseat)"

With `qemu-system-aarch64`:

    $> ./aarch64-softmmu/qemu-system-aarch64 -cpu help | head -5
    Available CPUs:
      arm1026
      arm1136
      arm1136-r2
      arm1176

    $> ./aarch64-softmmu/qemu-system-aarch64 -device help | head -5
    Controller/Bridge/Hub devices:
    name "i82801b11-bridge", bus PCI
    name "ioh3420", bus PCI, desc "Intel IOH device id 3420 PCIE Root Port"
    name "pci-bridge", bus PCI, desc "Standard PCI Bridge"
    name "pci-bridge-seat", bus PCI, desc "Standard PCI Bridge (multiseat)"

> Since the list of CPUs doesn't depend on the machine, this is
> unnecessarily unhelpful. "-device help" has a similar problem.
> 
> Move the checks for "did the user ask for -cpu help or -device help"
> up so they precede the select_machine() call which checks that the
> user specified a valid machine type.
> 
> Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

Tested-by: Kashyap Chamarthy <kchamart@redhat.com>

> ---
> This has been on-and-off irritating me for years, and it's
> embarrassing how simple the fix turns out to be...
> ---
>  softmmu/vl.c | 26 ++++++++++++++++----------
>  1 file changed, 16 insertions(+), 10 deletions(-)

[...] 

Thanks. :)

-- 
/kashyap