Re: [PATCH v3] qapi: give available enum values as error hint

[Markus Armbruster]

marcandre.lureau@redhat.com writes:

> From: Marc-André Lureau <marcandre.lureau@redhat.com>
>
> This allows for a more pleasant user experience.
>
> Before:
> $ ./qemu-system-x86_64 -display egl-headless,gl=
> qemu-system-x86_64: -display egl-headless,gl=: Parameter 'gl' does not accept 
> value ''
>
> After:
> $ ./qemu-system-x86_64 -display egl-headless,gl=
> qemu-system-x86_64: -display egl-headless,gl=: Parameter 'gl' does not accept 
> value ''
> Acceptable values are 'off', 'on', 'core', 'es'
>
> Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>

Nice improvement here.

Slightly ugly:

    $ qemu-system-x86_64 -nic bad
    upstream-qemu: -nic bad: Parameter 'type' does not accept value 'bad'
    Acceptable values are 'none', 'nic', 'user', 'tap', 'l2tpv3', 'socket', 
'stream', 'dgram', 'vde', 'bridge', 'hubport', 'netmap', 'vhost-user', 
'vhost-vdpa'

Outright annoying:

$ upstream-qemu -object bad
upstream-qemu: -object bad: Parameter 'qom-type' does not accept value 'bad'
Acceptable values are 'authz-list', 'authz-listfile', 'authz-pam', 
'authz-simple', 'can-bus', 'can-host-socketcan', 'colo-compare', 
'cryptodev-backend', 'cryptodev-backend-builtin', 'cryptodev-backend-lkcf', 
'dbus-vmstate', 'filter-buffer', 'filter-dump', 'filter-mirror', 
'filter-redirector', 'filter-replay', 'filter-rewriter', 'input-barrier', 
'input-linux', 'iothread', 'main-loop', 'memory-backend-epc', 
'memory-backend-file', 'memory-backend-memfd', 'memory-backend-ram', 
'pef-guest', 'pr-manager-helper', 'qtest', 'rng-builtin', 'rng-egd', 
'rng-random', 'secret', 'secret_keyring', 'sev-guest', 'thread-context', 
's390-pv-guest', 'throttle-group', 'tls-creds-anon', 'tls-creds-psk', 
'tls-creds-x509', 'tls-cipher-suites', 'x-remote-object', 'x-vfio-user-server'

Note we already let users ask for this information with -object help or
-object qom-type=help.  Sadly, we can't hint at that here, because it's
implemented much further up the call chain, and other call chains don't.

If HMP command sendkey didn't bypass the input visitor, the 26 screen
lines of hint for QKeyCode would likely scroll the error message off the
screen.

Should we suppress this hint when it's too long to be useful?