qapi: Document visitor interfaces, add assertions
commitadfb264c9ed04bfc694921b72173be8e29e90024
authorEric Blake <eblake@redhat.com>
Thu, 28 Apr 2016 21:45:20 +0000 (28 15:45 -0600)
committerMarkus Armbruster <armbru@redhat.com>
Thu, 12 May 2016 07:47:54 +0000 (12 09:47 +0200)
treef30741b641b2d2a4cf38cf5fa7c80e5f4dae2343
parentfcf3cb21783b2dae3358fdbe7001cb2f74e0cedf
qapi: Document visitor interfaces, add assertions

The visitor interface for mapping between QObject/QemuOpts/string
and QAPI is scandalously under-documented, making changes to visitor
core, individual visitors, and users of visitors difficult to
coordinate.  Among other questions: when is it safe to pass NULL,
vs. when a string must be provided; which visitors implement which
callbacks; the difference between concrete and virtual visits.

Correct this by retrofitting proper contracts, and document where some
of the interface warts remain (for example, we may want to modify
visit_end_* to require the same 'obj' as the visit_start counterpart,
so the dealloc visitor can be simplified).  Later patches in this
series will tackle some, but not all, of these warts.

Add assertions to (partially) enforce the contract.  Some of these
were only made possible by recent cleanup commits.

Signed-off-by: Eric Blake <eblake@redhat.com>
Message-Id: <1461879932-9020-13-git-send-email-eblake@redhat.com>
[Doc fix from Eric squashed in]
Signed-off-by: Markus Armbruster <armbru@redhat.com>
include/qapi/dealloc-visitor.h
include/qapi/opts-visitor.h
include/qapi/string-input-visitor.h
include/qapi/string-output-visitor.h
include/qapi/visitor-impl.h
include/qapi/visitor.h
qapi/qapi-visit-core.c