Re: [Qemu-devel] [PATCH 02/21] libqtest: Work around a "QMP wants a newline" bug

[Eric Blake]

On 02/23/2017 03:44 PM, Markus Armbruster wrote:
> The next commit is going to add a test that calls qmp("null").
> Curiously, this hangs.  Here's why.
> 
> qmp_fd_sendv() doesn't send newlines.  Not even when @fmt contains
> some.  At first glance, the QMP parser seems to be fine with that.
> However, it turns out that it fails to react to input until it sees
> either a newline, an object or an array.  To reproduce, feed to a QMP
> monitor like this:
> 

> 
> Work around this QMP bug by having qmp_fd_sendv() append a newline.
> 
> Signed-off-by: Markus Armbruster <address@hidden>
> ---
>  tests/libqtest.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 

> +++ b/tests/libqtest.c
> @@ -442,14 +442,20 @@ void qmp_fd_sendv(int fd, const char *fmt, va_list ap)
>      if (qobj) {
>          int log = getenv("QTEST_LOG") != NULL;
>          QString *qstr = qobject_to_json(qobj);
> -        const char *str = qstring_get_str(qstr);
> -        size_t size = qstring_get_length(qstr);
> +        const char *str;
> +
> +        /*
> +         * BUG: QMP doesn't react to input until it sees a newline, an
> +         * object, or an array.  Work-around: give it a newline.
> +         */
> +        qstring_append_chr(qstr, '\n');
> +        str = qstring_get_str(qstr);
>  
>          if (log) {
>              fprintf(stderr, "%s", str);

Bonus - the log now has newlines, too :)

>          }
>          /* Send QMP request */
> -        socket_send(fd, str, size);
> +        socket_send(fd, str, qstring_get_length(qstr));

Reviewed-by: Eric Blake <address@hidden>

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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