Re: [Qemu-devel] [PATCH 1/2] QemuOpts: introduce qemu_find_opts_singleton

[Laszlo Ersek <lersek@redhat.com>]

comments below

On 02/06/14 09:16, Igor Mammedov wrote:
> From: Paolo Bonzini <pbonzini@redhat.com>
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
>  include/qemu/config-file.h |    2 ++
>  util/qemu-config.c         |   14 ++++++++++++++
>  vl.c                       |   11 +----------
>  3 files changed, 17 insertions(+), 10 deletions(-)
> 
> diff --git a/include/qemu/config-file.h b/include/qemu/config-file.h
> index dbd97c4..d4ba20e 100644
> --- a/include/qemu/config-file.h
> +++ b/include/qemu/config-file.h
> @@ -8,6 +8,8 @@
>  
>  QemuOptsList *qemu_find_opts(const char *group);
>  QemuOptsList *qemu_find_opts_err(const char *group, Error **errp);
> +QemuOpts *qemu_find_opts_singleton(const char *group);
> +
>  void qemu_add_opts(QemuOptsList *list);
>  void qemu_add_drive_opts(QemuOptsList *list);
>  int qemu_set_option(const char *str);
> diff --git a/util/qemu-config.c b/util/qemu-config.c
> index 9298f55..9dfacbc 100644
> --- a/util/qemu-config.c
> +++ b/util/qemu-config.c
> @@ -39,6 +39,20 @@ QemuOptsList *qemu_find_opts(const char *group)
>      return ret;
>  }
>  
> +QemuOpts *qemu_find_opts_singleton(const char *group)
> +{
> +    QemuOptsList *list;
> +    QemuOpts *opts;
> +
> +    list = qemu_find_opts(group);
> +    assert(list);
> +    opts = qemu_opts_find(list, NULL);
> +    if (!opts) {
> +        opts = qemu_opts_create(list, NULL, 0, &error_abort);
> +    }
> +    return opts;
> +}

First of all, the commit message body is empty, and the subject line
doesn't really say much, plus there are no comments, so I have no clue
what we're trying to implement here *in general*.

For example, if you look into qemu_opts_create(), you'll see that when
(id==NULL), then you don't actually need the

  qemu_opts_find(list, NULL)

call, because qemu_opts_create() calls that itself anyway. Of course,
this behavior *also* depends on merge_lists being "true", but in case of
"machine", that *is* a given.

Hence a specification for the function would help deciding if we can
take merge_lists for granted, or if we want something more general. In
the former case, the code above is unnecessarily pessimistic.

(Basically the qemu_find_opts_singleton() should be a *very* thin
wrapper around qemu_opts_create(), because the latter already has this
"O_CREAT without O_EXCL" semantics.)

> +
>  static CommandLineParameterInfoList *query_option_descs(const QemuOptDesc *desc)
>  {
>      CommandLineParameterInfoList *param_list = NULL, *entry;
> diff --git a/vl.c b/vl.c
> index 383be1b..7f2595c 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -539,16 +539,7 @@ static QemuOptsList qemu_msg_opts = {
>   */
>  QemuOpts *qemu_get_machine_opts(void)
>  {
> -    QemuOptsList *list;
> -    QemuOpts *opts;
> -
> -    list = qemu_find_opts("machine");
> -    assert(list);
> -    opts = qemu_opts_find(list, NULL);
> -    if (!opts) {
> -        opts = qemu_opts_create(list, NULL, 0, &error_abort);
> -    }
> -    return opts;
> +    return qemu_find_opts_singleton("machine");
>  }
>  
>  const char *qemu_get_vm_name(void)
> 

I also kinda hate that "error_abort" -- while used in several
option-specific parser functions (balloon_parse, virtcon_parse,
QEMU_OPTION_virtfs, QEMU_OPTION_virtfs_synth) -- now makes it into a
generic-looking options function. qemu_find_opts_singleton() should take
an errp.

Anyway I don't care enough to insist on a respin.

Reviewed-by: Laszlo Ersek <lersek@redhat.com>