Re: [Qemu-devel] [PATCH v3 03/12] qtest: Document calling conventions

[Markus Armbruster <armbru@redhat.com>]

Eric Blake <eblake@redhat.com> writes:

> We have two flavors of vararg usage in qtest; make it clear that
> qmp() has different semantics than hmp(), and let the compiler
> enforce that hmp() is used correctly. However, qmp() (and friends)
> only accept a subset of printf flags look-alikes (namely, those
> that our JSON parser understands), and what is worse, qmp("true")
> (the JSON keyword 'true') is different from qmp("%s", "true")
> (the JSON string '"true"'), and we have some intermediate cleanup
> patches to do before we can mark those as printf-like.

It's not "worse", it's just different :)

Suggest:

  We have two flavors of vararg usage in qtest: qtest_hmp() etc. work
  like sprintf(), and qtest_qmp() etc. work like qobject_from_jsonf().
  Spell that out in the comments.

  Also add GCC_FMT_ATTR() to qtest_hmp() etc. so that the compiler can
  flag incorrect use.

  We have some cleanup work to do before we can do the same for
  qtest_qmp() etc.  This will get us the same better-than-nothing
  checking we already have for qobject_from_jsonf(): common incorrect
  uses of supported conversion specifications will be flagged
  (e.g. passing a double for %d), but use of unsupported ones won't.

Note that my text omits most of the details that aren't directly
relevant to the patch.

>
> Signed-off-by: Eric Blake <eblake@redhat.com>
>
> ---
> v3: restore lost attributes, add comments on va_list forms, tweak
> commit message to mention upcoming qmp cleanups
> v2: several comment tweaks, explain why qmp() can't be marked
> ---
>  tests/libqtest.h | 40 +++++++++++++++++++++++++---------------
>  1 file changed, 25 insertions(+), 15 deletions(-)
>
> diff --git a/tests/libqtest.h b/tests/libqtest.h
> index 38bc1e9953..82e89b4d4f 100644
> --- a/tests/libqtest.h
> +++ b/tests/libqtest.h
> @@ -50,7 +50,8 @@ void qtest_quit(QTestState *s);
>  /**
>   * qtest_qmp_discard_response:
>   * @s: #QTestState instance to operate on.
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and consumes the response.
>   */
> @@ -59,7 +60,8 @@ void qtest_qmp_discard_response(QTestState *s, const char *fmt, ...);
>  /**
>   * qtest_qmp:
>   * @s: #QTestState instance to operate on.
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and returns the response.
>   */
> @@ -68,7 +70,8 @@ QDict *qtest_qmp(QTestState *s, const char *fmt, ...);
>  /**
>   * qtest_async_qmp:
>   * @s: #QTestState instance to operate on.
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and leaves the response in the stream.
>   */
> @@ -77,7 +80,8 @@ void qtest_async_qmp(QTestState *s, const char *fmt, ...);
>  /**
>   * qtest_qmpv_discard_response:
>   * @s: #QTestState instance to operate on.
> - * @fmt: QMP message to send to QEMU
> + * @fmt: QMP message to send to QEMU; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   * @ap: QMP message arguments
>   *
>   * Sends a QMP message to QEMU and consumes the response.
> @@ -87,7 +91,8 @@ void qtest_qmpv_discard_response(QTestState *s, const char *fmt, va_list ap);
>  /**
>   * qtest_qmpv:
>   * @s: #QTestState instance to operate on.
> - * @fmt: QMP message to send to QEMU
> + * @fmt: QMP message to send to QEMU; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   * @ap: QMP message arguments
>   *
>   * Sends a QMP message to QEMU and returns the response.
> @@ -97,7 +102,8 @@ QDict *qtest_qmpv(QTestState *s, const char *fmt, va_list ap);
>  /**
>   * qtest_async_qmpv:
>   * @s: #QTestState instance to operate on.
> - * @fmt: QMP message to send to QEMU
> + * @fmt: QMP message to send to QEMU; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   * @ap: QMP message arguments
>   *
>   * Sends a QMP message to QEMU and leaves the response in the stream.
> @@ -134,19 +140,19 @@ QDict *qtest_qmp_eventwait_ref(QTestState *s, const char *event);
>  /**
>   * qtest_hmp:
>   * @s: #QTestState instance to operate on.
> - * @fmt...: HMP command to send to QEMU
> + * @fmt...: HMP command to send to QEMU, formats arguments like vsprintf().

Like sprintf().

>   *
>   * Send HMP command to QEMU via QMP's human-monitor-command.
>   * QMP events are discarded.
>   *
>   * Returns: the command's output.  The caller should g_free() it.
>   */
> -char *qtest_hmp(QTestState *s, const char *fmt, ...);
> +char *qtest_hmp(QTestState *s, const char *fmt, ...) GCC_FMT_ATTR(2, 3);
>
>  /**
>   * qtest_hmpv:
>   * @s: #QTestState instance to operate on.
> - * @fmt: HMP command to send to QEMU
> + * @fmt: HMP command to send to QEMU, formats arguments like vsprintf().
>   * @ap: HMP command arguments
>   *
>   * Send HMP command to QEMU via QMP's human-monitor-command.
> @@ -154,7 +160,8 @@ char *qtest_hmp(QTestState *s, const char *fmt, ...);
>   *
>   * Returns: the command's output.  The caller should g_free() it.
>   */
> -char *qtest_hmpv(QTestState *s, const char *fmt, va_list ap);
> +char *qtest_hmpv(QTestState *s, const char *fmt, va_list ap)
> +    GCC_FMT_ATTR(2, 0);
>
>  /**
>   * qtest_get_irq:
> @@ -535,7 +542,8 @@ static inline void qtest_end(void)
>
>  /**
>   * qmp:
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and returns the response.
>   */
> @@ -543,7 +551,8 @@ QDict *qmp(const char *fmt, ...);
>
>  /**
>   * qmp_async:
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and leaves the response in the stream.
>   */
> @@ -551,7 +560,8 @@ void qmp_async(const char *fmt, ...);
>
>  /**
>   * qmp_discard_response:
> - * @fmt...: QMP message to send to qemu
> + * @fmt...: QMP message to send to qemu; formats arguments through
> + * json-lexer.c (only understands '%(PRI[ud]64|(l|ll)?[du]|[ipsf])').
>   *
>   * Sends a QMP message to QEMU and consumes the response.
>   */
> @@ -592,13 +602,13 @@ static inline QDict *qmp_eventwait_ref(const char *event)
>
>  /**
>   * hmp:
> - * @fmt...: HMP command to send to QEMU
> + * @fmt...: HMP command to send to QEMU, formats arguments like vsprintf().
>   *
>   * Send HMP command to QEMU via QMP's human-monitor-command.
>   *
>   * Returns: the command's output.  The caller should g_free() it.
>   */
> -char *hmp(const char *fmt, ...);
> +char *hmp(const char *fmt, ...) GCC_FMT_ATTR(1, 2);
>
>  /**
>   * get_irq:

With the comment fixed, and preferably with an improved commit message:
Reviewed-by: Markus Armbruster <armbru@redhat.com>