Placing GenericList in util.h will make it easier for the next patch
to promote QAPI_LIST_ADD() into a public macro without requiring more
files to include the unrelated visitor.h.

However, we can't also move GenericAlternate; this is because it would
introduce a circular dependency: qapi-builtin-types.h needs a complete
definition of QEnumLookup (so it includes qapi/util.h), and
GenericAlternate needs a complete definition of QType (declared in
qapi-builtin-types.h).  Leaving GenericAlternate in visitor.h breaks
the cycle, and doesn't matter since we don't have any further planned
uses for that type outside of visitors.

Suggested-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Eric Blake <eblake@redhat.com>
---
 include/qapi/visitor.h | 9 +--------
 include/qapi/util.h    | 8 ++++++++
 2 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
index ebc19ede7fff..8c2e1c29ad8b 100644
--- a/include/qapi/visitor.h
+++ b/include/qapi/visitor.h
@@ -16,6 +16,7 @@
 #define QAPI_VISITOR_H

 #include "qapi/qapi-builtin-types.h"
+#include "qapi/util.h"

 /*
  * The QAPI schema defines both a set of C data types, and a QMP wire
@@ -228,14 +229,6 @@

 /*** Useful types ***/

-/* This struct is layout-compatible with all other *List structs
- * created by the QAPI generator.  It is used as a typical
- * singly-linked list. */
-typedef struct GenericList {
-    struct GenericList *next;
-    char padding[];
-} GenericList;
-
 /* This struct is layout-compatible with all Alternate types
  * created by the QAPI generator. */
 typedef struct GenericAlternate {
diff --git a/include/qapi/util.h b/include/qapi/util.h
index a7c3c6414874..50201896c7a4 100644
--- a/include/qapi/util.h
+++ b/include/qapi/util.h
@@ -11,6 +11,14 @@
 #ifndef QAPI_UTIL_H
 #define QAPI_UTIL_H

+/* This struct is layout-compatible with all other *List structs
+ * created by the QAPI generator.  It is used as a typical
+ * singly-linked list. */
+typedef struct GenericList {
+    struct GenericList *next;
+    char padding[];
+} GenericList;
+
 typedef struct QEnumLookup {
     const char *const *array;
     int size;
-- 
2.29.0

Eric Blake <eblake@redhat.com> writes:

> Placing GenericList in util.h will make it easier for the next patch
> to promote QAPI_LIST_ADD() into a public macro without requiring more
> files to include the unrelated visitor.h.

Is this true?

You don't actually need GenericList to make use of QAPI_LIST_ADD(), do
you?  Any QAPI list type should do.

> However, we can't also move GenericAlternate; this is because it would
> introduce a circular dependency: qapi-builtin-types.h needs a complete
> definition of QEnumLookup (so it includes qapi/util.h), and
> GenericAlternate needs a complete definition of QType (declared in
> qapi-builtin-types.h).  Leaving GenericAlternate in visitor.h breaks
> the cycle, and doesn't matter since we don't have any further planned
> uses for that type outside of visitors.
>
> Suggested-by: Markus Armbruster <armbru@redhat.com>

I did suggest to consider moving GenericList and GenericAlternate next
to QAPI_LIST_ADD(), because they're (loosely) related.  We can't move
GenericAlternate.  Moving only GenericList brings GenericList and
QAPI_LIST_ADD() together, but separates the more closely related
GenericList and GenericAlternate.  Meh.

I'd leave it put.

> Signed-off-by: Eric Blake <eblake@redhat.com>
> ---
>  include/qapi/visitor.h | 9 +--------
>  include/qapi/util.h    | 8 ++++++++
>  2 files changed, 9 insertions(+), 8 deletions(-)
>
> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
> index ebc19ede7fff..8c2e1c29ad8b 100644
> --- a/include/qapi/visitor.h
> +++ b/include/qapi/visitor.h
> @@ -16,6 +16,7 @@
>  #define QAPI_VISITOR_H
>
>  #include "qapi/qapi-builtin-types.h"
> +#include "qapi/util.h"

Not necessary, qapi-builtin-types.h must include it for QEnumLookup.

>  /*
>   * The QAPI schema defines both a set of C data types, and a QMP wire
> @@ -228,14 +229,6 @@
>
>  /*** Useful types ***/
>
> -/* This struct is layout-compatible with all other *List structs
> - * created by the QAPI generator.  It is used as a typical
> - * singly-linked list. */
> -typedef struct GenericList {
> -    struct GenericList *next;
> -    char padding[];
> -} GenericList;
> -
>  /* This struct is layout-compatible with all Alternate types
>   * created by the QAPI generator. */
>  typedef struct GenericAlternate {
> diff --git a/include/qapi/util.h b/include/qapi/util.h
> index a7c3c6414874..50201896c7a4 100644
> --- a/include/qapi/util.h
> +++ b/include/qapi/util.h
> @@ -11,6 +11,14 @@
>  #ifndef QAPI_UTIL_H
>  #define QAPI_UTIL_H
>
> +/* This struct is layout-compatible with all other *List structs
> + * created by the QAPI generator.  It is used as a typical
> + * singly-linked list. */
> +typedef struct GenericList {
> +    struct GenericList *next;
> +    char padding[];
> +} GenericList;
> +
>  typedef struct QEnumLookup {
>      const char *const *array;
>      int size;

On 10/26/20 9:18 AM, Markus Armbruster wrote:
> Eric Blake <eblake@redhat.com> writes:
> 
>> Placing GenericList in util.h will make it easier for the next patch
>> to promote QAPI_LIST_ADD() into a public macro without requiring more
>> files to include the unrelated visitor.h.
> 
> Is this true?
> 
> You don't actually need GenericList to make use of QAPI_LIST_ADD(), do
> you?  Any QAPI list type should do.

Correct, compilation still works if I drop this patch.

> 
>> However, we can't also move GenericAlternate; this is because it would
>> introduce a circular dependency: qapi-builtin-types.h needs a complete
>> definition of QEnumLookup (so it includes qapi/util.h), and
>> GenericAlternate needs a complete definition of QType (declared in
>> qapi-builtin-types.h).  Leaving GenericAlternate in visitor.h breaks
>> the cycle, and doesn't matter since we don't have any further planned
>> uses for that type outside of visitors.
>>
>> Suggested-by: Markus Armbruster <armbru@redhat.com>
> 
> I did suggest to consider moving GenericList and GenericAlternate next
> to QAPI_LIST_ADD(), because they're (loosely) related.  We can't move
> GenericAlternate.  Moving only GenericList brings GenericList and
> QAPI_LIST_ADD() together, but separates the more closely related
> GenericList and GenericAlternate.  Meh.
> 
> I'd leave it put.

Agreed. Dropping this patch in v6.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

23.10.2020 21:36, Eric Blake wrote:
> Placing GenericList in util.h will make it easier for the next patch
> to promote QAPI_LIST_ADD() into a public macro without requiring more
> files to include the unrelated visitor.h.
> 
> However, we can't also move GenericAlternate; this is because it would
> introduce a circular dependency: qapi-builtin-types.h needs a complete
> definition of QEnumLookup (so it includes qapi/util.h), and
> GenericAlternate needs a complete definition of QType (declared in
> qapi-builtin-types.h).  Leaving GenericAlternate in visitor.h breaks
> the cycle, and doesn't matter since we don't have any further planned
> uses for that type outside of visitors.
> 
> Suggested-by: Markus Armbruster <armbru@redhat.com>
> Signed-off-by: Eric Blake <eblake@redhat.com>

Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>

> ---
>   include/qapi/visitor.h | 9 +--------
>   include/qapi/util.h    | 8 ++++++++
>   2 files changed, 9 insertions(+), 8 deletions(-)
> 
> diff --git a/include/qapi/visitor.h b/include/qapi/visitor.h
> index ebc19ede7fff..8c2e1c29ad8b 100644
> --- a/include/qapi/visitor.h
> +++ b/include/qapi/visitor.h
> @@ -16,6 +16,7 @@
>   #define QAPI_VISITOR_H
> 
>   #include "qapi/qapi-builtin-types.h"
> +#include "qapi/util.h"
> 
>   /*
>    * The QAPI schema defines both a set of C data types, and a QMP wire
> @@ -228,14 +229,6 @@
> 
>   /*** Useful types ***/
> 
> -/* This struct is layout-compatible with all other *List structs
> - * created by the QAPI generator.  It is used as a typical
> - * singly-linked list. */
> -typedef struct GenericList {
> -    struct GenericList *next;
> -    char padding[];
> -} GenericList;
> -
>   /* This struct is layout-compatible with all Alternate types
>    * created by the QAPI generator. */
>   typedef struct GenericAlternate {
> diff --git a/include/qapi/util.h b/include/qapi/util.h
> index a7c3c6414874..50201896c7a4 100644
> --- a/include/qapi/util.h
> +++ b/include/qapi/util.h
> @@ -11,6 +11,14 @@
>   #ifndef QAPI_UTIL_H
>   #define QAPI_UTIL_H
> 
> +/* This struct is layout-compatible with all other *List structs
> + * created by the QAPI generator.  It is used as a typical
> + * singly-linked list. */

doesn't checkpatch complain for comment style?

> +typedef struct GenericList {
> +    struct GenericList *next;
> +    char padding[];
> +} GenericList;
> +
>   typedef struct QEnumLookup {
>       const char *const *array;
>       int size;
> 


-- 
Best regards,
Vladimir