Re: [PATCH v2] qapi: enable use of g_autoptr with QAPI types

[Markus Armbruster <armbru@redhat.com>]

Daniel P. Berrangé <berrange@redhat.com> writes:

> Currently QAPI generates a type and function for free'ing it:
>
>   typedef struct QCryptoBlockCreateOptions QCryptoBlockCreateOptions;
>   void qapi_free_QCryptoBlockCreateOptions(QCryptoBlockCreateOptions *obj);
>
> This is used in the traditional manner:
>
>   QCryptoBlockCreateOptions *opts = NULL;
>
>   opts = g_new0(QCryptoBlockCreateOptions, 1);
>
>   ....do stuff with opts...
>
>   qapi_free_QCryptoBlockCreateOptions(opts);
>
> Since bumping the min glib to 2.48, QEMU has incrementally adopted the
> use of g_auto/g_autoptr. This allows the compiler to run a function to
> free a variable when it goes out of scope, the benefit being the
> compiler can guarantee it is freed in all possible code ptahs.
>
> This benefit is applicable to QAPI types too, and given the seriously
> long method names for some qapi_free_XXXX() functions, is much less
> typing. This change thus makes the code generator emit:
>
>  G_DEFINE_AUTOPTR_CLEANUP_FUNC(QCryptoBlockCreateOptions,
>                               qapi_free_QCryptoBlockCreateOptions)
>
> The above code example now becomes
>
>   g_autoptr(QCryptoBlockCreateOptions) opts = NULL;
>
>   opts = g_new0(QCryptoBlockCreateOptions, 1);
>
>   ....do stuff with opts...
>
> Note, if the local pointer needs to live beyond the scope holding the
> variable, then g_steal_pointer can be used. This is useful to return the
> pointer to the caller in the success codepath, while letting it be freed
> in all error codepaths.
>
>   return g_steal_pointer(&opts);
>
> The crypto/block.h header needs updating to avoid symbol clash now that
> the g_autoptr support is a standard QAPI feature.
>
> Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>

Queued for 5.2, thanks!