Re: [Qemu-devel] [PATCH v2] Fix the -accel parameter and the documentation for 'hax'

[Markus Armbruster <armbru@redhat.com>]

Thomas Huth <thuth@redhat.com> writes:

> Since 'hax' is a possible accelerator nowadays, too, the '-accel'
> option should support it and we should mention this accelerator
> in the documentation, too.
>
> Signed-off-by: Thomas Huth <thuth@redhat.com>
> ---
>  v2:
>  - Use qemu_opt_set() instead of qemu_opts_parse_noisily()
>  - Improve the documentation of the -accel option
>
>  qemu-options.hx | 18 +++++++++---------
>  vl.c            | 23 +++++++++--------------
>  2 files changed, 18 insertions(+), 23 deletions(-)
>
> diff --git a/qemu-options.hx b/qemu-options.hx
> index 787b9c3..21f8ff2 100644
> --- a/qemu-options.hx
> +++ b/qemu-options.hx
> @@ -31,7 +31,7 @@ DEF("machine", HAS_ARG, QEMU_OPTION_machine, \
>      "-machine [type=]name[,prop[=value][,...]]\n"
>      "                selects emulated machine ('-machine help' for list)\n"
>      "                property accel=accel1[:accel2[:...]] selects accelerator\n"
> -    "                supported accelerators are kvm, xen, tcg (default: tcg)\n"
> +    "                supported accelerators are kvm, xen, hax or tcg (default: tcg)\n"

The list of accelerators is approaching a length where sorting may make
sense.  You decide.

>      "                kernel_irqchip=on|off|split controls accelerated irqchip support (default=off)\n"
>      "                vmport=on|off|auto controls emulation of vmport (default: auto)\n"
>      "                kvm_shadow_mem=size of KVM shadow MMU in bytes\n"
> @@ -52,9 +52,9 @@ available machines. Supported machine properties are:
>  @table @option
>  @item accel=@var{accels1}[:@var{accels2}[:...]]
>  This is used to enable an accelerator. Depending on the target architecture,
> -kvm, xen, or tcg can be available. By default, tcg is used. If there is more
> -than one accelerator specified, the next one is used if the previous one fails
> -to initialize.
> +kvm, xen, hax or tcg can be available. By default, tcg is used. If there is
> +more than one accelerator specified, the next one is used if the previous one
> +fails to initialize.
>  @item kernel_irqchip=on|off
>  Controls in-kernel irqchip support for the chosen accelerator when available.
>  @item gfx_passthru=on|off
> @@ -97,15 +97,15 @@ ETEXI
>  
>  DEF("accel", HAS_ARG, QEMU_OPTION_accel,
>      "-accel [accel=]accelerator[,thread=single|multi]\n"
> -    "               select accelerator ('-accel help for list')\n"
> -    "               thread=single|multi (enable multi-threaded TCG)", QEMU_ARCH_ALL)
> +    "                select accelerator (kvm, xen, hax or tcg; use 'help' for a list)\n"
> +    "                thread=single|multi (enable multi-threaded TCG)", QEMU_ARCH_ALL)

Thanks for fixing help indentation while there.

>  STEXI
>  @item -accel @var{name}[,prop=@var{value}[,...]]
>  @findex -accel
>  This is used to enable an accelerator. Depending on the target architecture,
> -kvm, xen, or tcg can be available. By default, tcg is used. If there is more
> -than one accelerator specified, the next one is used if the previous one fails
> -to initialize.
> +kvm, xen, hax or tcg can be available. By default, tcg is used. If there is
> +more than one accelerator specified, the next one is used if the previous one
> +fails to initialize.
>  @table @option
>  @item thread=single|multi
>  Controls number of TCG threads. When the TCG is multi-threaded there will be one
> diff --git a/vl.c b/vl.c
> index f46e070..0a1b931 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -3725,26 +3725,21 @@ int main(int argc, char **argv, char **envp)
>                  qdev_prop_register_global(&kvm_pit_lost_tick_policy);
>                  break;
>              }
> -            case QEMU_OPTION_accel:
> +            case QEMU_OPTION_accel: {
> +                QemuOpts *accel_opts;

Doesn't this shadow the @accel_opts declared in main()'s outermost
scope?

What's wrong with using @opts for its intended purpose here?

> +
>                  accel_opts = qemu_opts_parse_noisily(qemu_find_opts("accel"),
>                                                       optarg, true);
>                  optarg = qemu_opt_get(accel_opts, "accel");

Abusing optarg this way is not nice.  It should be assigned to only once
per iteration, via lookup_opt().  Not your fault, but perhaps you'd like
to clean it up anyway.

Even more pointless abuse in case QEMU_OPTION_rotate.  That one should
be converted to qemu_strtol().  Separate patch, and not required to get
my blessings for this one.

> -
> -                olist = qemu_find_opts("machine");
> -                if (strcmp("kvm", optarg) == 0) {
> -                    qemu_opts_parse_noisily(olist, "accel=kvm", false);
> -                } else if (strcmp("xen", optarg) == 0) {
> -                    qemu_opts_parse_noisily(olist, "accel=xen", false);
> -                } else if (strcmp("tcg", optarg) == 0) {
> -                    qemu_opts_parse_noisily(olist, "accel=tcg", false);
> -                } else {
> -                    if (!is_help_option(optarg)) {
> -                        error_printf("Unknown accelerator: %s", optarg);
> -                    }
> -                    error_printf("Supported accelerators: kvm, xen, tcg\n");
> +                if (!optarg || is_help_option(optarg)) {
> +                    error_printf("Possible accelerators: kvm, xen, hax, tcg\n");
>                      exit(1);

Not your patch's fault, but trivial to fix now: this should be exit(0),
as asking for help is not an error.

>                  }
> +                accel_opts = qemu_opts_create(qemu_find_opts("machine"), NULL,
> +                                              false, &error_abort);
> +                qemu_opt_set(accel_opts, "accel", optarg, &error_abort);

The switch from qemu_opt_set() to qemu_opts_parse_noisily() makes
desugaring less explicit, but also less repetitive.  Okay.

Hmm, where did the "Unknown accelerator" error go?  Aha:

    $ qemu-system-x86_64 -accel xxx
    "xxx" accelerator not found.
    No accelerator found!

Two error messages instead of one, and I don't care for the overexcited
'!', but that's all beyond this patch's scope.

>                  break;
> +            }
>              case QEMU_OPTION_usb:
>                  olist = qemu_find_opts("machine");
>                  qemu_opts_parse_noisily(olist, "usb=on", false);