examples: skip example when missing dependencies

  Trying to disable the vhost library, meson will complain it can't build
the vhost* and vdpa examples when passing -Dexamples=all.

-Dexamples=all skips examples if the example itself announces it can't
be built (for external dependencies, internal dependencies and other
reasons).
Since examples/meson.build will evaluate the internal dependencies
in any case, let's move the check there and resolve the issue for
optional internal libraries.

Fixes: 0bf583222297 ("lib: allow disabling optional libraries")

Signed-off-by: David Marchand <david.marchand@redhat.com>
---
 examples/distributor/meson.build              |  6 -----
 examples/kni/meson.build                      |  6 -----
 examples/l3fwd-power/meson.build              |  5 ----
 examples/meson.build                          | 24 ++++++++++++-------
 examples/vhost_crypto/meson.build             |  5 ----
 .../vm_power_manager/guest_cli/meson.build    |  5 ----
 examples/vm_power_manager/meson.build         |  5 ----
 7 files changed, 16 insertions(+), 40 deletions(-)
  

On Fri, Nov 05, 2021 at 02:30:55PM +0100, David Marchand wrote:
> Trying to disable the vhost library, meson will complain it can't build
> the vhost* and vdpa examples when passing -Dexamples=all.
> 
> -Dexamples=all skips examples if the example itself announces it can't
> be built (for external dependencies, internal dependencies and other
> reasons).
> Since examples/meson.build will evaluate the internal dependencies
> in any case, let's move the check there and resolve the issue for
> optional internal libraries.
> 
> Fixes: 0bf583222297 ("lib: allow disabling optional libraries")
> 
> Signed-off-by: David Marchand <david.marchand@redhat.com>

One comment inline below, otherwise looks a good change.

Acked-by: Bruce Richardson <bruce.richardson@intel.com>

> ---
>  examples/distributor/meson.build              |  6 -----
>  examples/kni/meson.build                      |  6 -----
>  examples/l3fwd-power/meson.build              |  5 ----
>  examples/meson.build                          | 24 ++++++++++++-------
>  examples/vhost_crypto/meson.build             |  5 ----
>  .../vm_power_manager/guest_cli/meson.build    |  5 ----
>  examples/vm_power_manager/meson.build         |  5 ----
>  7 files changed, 16 insertions(+), 40 deletions(-)
> 
> diff --git a/examples/distributor/meson.build b/examples/distributor/meson.build
> index 9df59923ce..ca1eca952e 100644
> --- a/examples/distributor/meson.build
> +++ b/examples/distributor/meson.build
> @@ -6,12 +6,6 @@
>  # To build this example as a standalone application with an already-installed
>  # DPDK instance, use 'make'
>  
> -# require the power library
> -build = dpdk_conf.has('RTE_LIB_POWER')
> -if not build
> -    subdir_done()
> -endif
> -
>  allow_experimental_apis = true
>  deps += ['distributor', 'power']
>  sources = files(
> diff --git a/examples/kni/meson.build b/examples/kni/meson.build
> index 1c0bf99a49..6bd4eb50e6 100644
> --- a/examples/kni/meson.build
> +++ b/examples/kni/meson.build
> @@ -6,12 +6,6 @@
>  # To build this example as a standalone application with an already-installed
>  # DPDK instance, use 'make'
>  
> -# this app can be built if-and-only-if KNI library is buildable
> -build = dpdk_conf.has('RTE_LIB_KNI')
> -if not build
> -    subdir_done()
> -endif
> -
>  deps += ['kni', 'bus_pci']
>  sources = files(
>          'main.c',
> diff --git a/examples/l3fwd-power/meson.build b/examples/l3fwd-power/meson.build
> index 0f69bb782c..624ef5e947 100644
> --- a/examples/l3fwd-power/meson.build
> +++ b/examples/l3fwd-power/meson.build
> @@ -6,11 +6,6 @@
>  # To build this example as a standalone application with an already-installed
>  # DPDK instance, use 'make'
>  
> -if not dpdk_conf.has('RTE_LIB_POWER')
> -        build = false
> -        subdir_done()
> -endif
> -
>  allow_experimental_apis = true
>  deps += ['power', 'timer', 'lpm', 'hash', 'metrics', 'telemetry']
>  sources = files(
> diff --git a/examples/meson.build b/examples/meson.build
> index d50f09db12..35ec3471af 100644
> --- a/examples/meson.build
> +++ b/examples/meson.build
> @@ -104,6 +104,22 @@ foreach example: examples
>      deps = ['eal', 'mempool', 'net', 'mbuf', 'ethdev', 'cmdline']
>      subdir(example)
>  
> +    if build
> +        dep_objs = ext_deps
> +        foreach d:deps
> +            if not build
> +                break
> +            endif

I believe this check can be removed by just putting "break" after the
"message()" call below.

> +            var_name = get_option('default_library') + '_rte_' + d
> +            if not is_variable(var_name)
> +                build = false
> +                message('Missing dependency "@0@" for example "@1@"'.format(d, name))
> +            else
> +                dep_objs += [get_variable(var_name)]
> +            endif
> +        endforeach
> +    endif
> +
  

On Fri, Nov 5, 2021 at 2:39 PM Bruce Richardson
<bruce.richardson@intel.com> wrote:
> > @@ -104,6 +104,22 @@ foreach example: examples
> >      deps = ['eal', 'mempool', 'net', 'mbuf', 'ethdev', 'cmdline']
> >      subdir(example)
> >
> > +    if build
> > +        dep_objs = ext_deps
> > +        foreach d:deps
> > +            if not build
> > +                break
> > +            endif
>
> I believe this check can be removed by just putting "break" after the
> "message()" call below.

I took the inspiration from drivers/meson.build (where I suppose, the
if not build in the loop is to catch a build = false set by the subdir
meson.build).
It's more readable with a break where expected.
v2 incoming.

>
> > +            var_name = get_option('default_library') + '_rte_' + d
> > +            if not is_variable(var_name)
> > +                build = false
> > +                message('Missing dependency "@0@" for example "@1@"'.format(d, name))
> > +            else
> > +                dep_objs += [get_variable(var_name)]
> > +            endif
> > +        endforeach
> > +    endif
> > +
>

Thanks.