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

[Daniel P . Berrangé]

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);

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/crypto/block.h | 2 --
 scripts/qapi/types.py  | 1 +
 2 files changed, 1 insertion(+), 2 deletions(-)

diff --git a/include/crypto/block.h b/include/crypto/block.h
index d274819791..7a65e8e402 100644
--- a/include/crypto/block.h
+++ b/include/crypto/block.h
@@ -311,7 +311,5 @@ uint64_t qcrypto_block_get_sector_size(QCryptoBlock *block);
 void qcrypto_block_free(QCryptoBlock *block);
 
 G_DEFINE_AUTOPTR_CLEANUP_FUNC(QCryptoBlock, qcrypto_block_free)
-G_DEFINE_AUTOPTR_CLEANUP_FUNC(QCryptoBlockCreateOptions,
-                              qapi_free_QCryptoBlockCreateOptions)
 
 #endif /* QCRYPTO_BLOCK_H */
diff --git a/scripts/qapi/types.py b/scripts/qapi/types.py
index 3ad33af4ee..3640f17cd6 100644
--- a/scripts/qapi/types.py
+++ b/scripts/qapi/types.py
@@ -213,6 +213,7 @@ def gen_type_cleanup_decl(name):
     ret = mcgen('''
 
 void qapi_free_%(c_name)s(%(c_name)s *obj);
+G_DEFINE_AUTOPTR_CLEANUP_FUNC(%(c_name)s, qapi_free_%(c_name)s)
 ''',
                 c_name=c_name(name))
     return ret
-- 
2.26.2