Re: [Qemu-devel] [PATCH v2] Add interface to traverse the qmp command list by QmpCommand

[Michael Roth <mdroth@linux.vnet.ibm.com>]

Quoting Mark Wu (2013-10-08 01:23:09)
> In the original code, qmp_get_command_list is used to construct
> a list of all commands' name. To get the information of all qga
> commands, it traverses the name list and search the command info
> with its name.  So it can cause O(n^2) in the number of commands.
> 
> This patch adds an interface to traverse the qmp command list by
> QmpCommand to replace qmp_get_command_list. It can decrease the
> complexity from O(n^2) to O(n).
> 
> Signed-off-by: Mark Wu <wudxw@linux.vnet.ibm.com>
> ---
> Changes:
> v2:
>         1. Keep the signature of qmp_command_is_enabled (per Eric and Michael)
>     2. Remove the unnecessary pointer castings (per Eric)
> 
>  include/qapi/qmp/dispatch.h |  5 ++--
>  qapi/qmp-registry.c         | 27 +++---------------
>  qga/commands.c              | 38 ++++++++++---------------
>  qga/main.c                  | 68 +++++++++++++++++----------------------------
>  4 files changed, 48 insertions(+), 90 deletions(-)
> 
> diff --git a/include/qapi/qmp/dispatch.h b/include/qapi/qmp/dispatch.h
> index 1ce11f5..b6eb49e 100644
> --- a/include/qapi/qmp/dispatch.h
> +++ b/include/qapi/qmp/dispatch.h
> @@ -47,9 +47,10 @@ QmpCommand *qmp_find_command(const char *name);
>  QObject *qmp_dispatch(QObject *request);
>  void qmp_disable_command(const char *name);
>  void qmp_enable_command(const char *name);
> -bool qmp_command_is_enabled(const char *name);
> -char **qmp_get_command_list(void);
> +bool qmp_command_is_enabled(const QmpCommand *cmd);
>  QObject *qmp_build_error_object(Error *errp);
> +typedef void (*qmp_cmd_callback_fn)(QmpCommand *cmd, void *opaque);
> +void qmp_for_each_command(qmp_cmd_callback_fn fn, void *opaque);
> 
>  #endif
> 
> diff --git a/qapi/qmp-registry.c b/qapi/qmp-registry.c
> index 28bbbe8..3fcf10e 100644
> --- a/qapi/qmp-registry.c
> +++ b/qapi/qmp-registry.c
> @@ -66,35 +66,16 @@ void qmp_enable_command(const char *name)
>      qmp_toggle_command(name, true);
>  }
> 
> -bool qmp_command_is_enabled(const char *name)
> +bool qmp_command_is_enabled(const QmpCommand *cmd)
>  {
> -    QmpCommand *cmd;
> -
> -    QTAILQ_FOREACH(cmd, &qmp_commands, node) {
> -        if (strcmp(cmd->name, name) == 0) {
> -            return cmd->enabled;
> -        }
> -    }
> -
> -    return false;
> +    return cmd->enabled;
>  }
> 
> -char **qmp_get_command_list(void)
> +void qmp_for_each_command(qmp_cmd_callback_fn fn, void *opaque)
>  {
>      QmpCommand *cmd;
> -    int count = 1;
> -    char **list_head, **list;
> -
> -    QTAILQ_FOREACH(cmd, &qmp_commands, node) {
> -        count++;
> -    }
> -
> -    list_head = list = g_malloc0(count * sizeof(char *));
> 
>      QTAILQ_FOREACH(cmd, &qmp_commands, node) {
> -        *list = g_strdup(cmd->name);
> -        list++;
> +        fn(cmd, opaque);
>      }
> -
> -    return list_head;
>  }
> diff --git a/qga/commands.c b/qga/commands.c
> index 528b082..063b22b 100644
> --- a/qga/commands.c
> +++ b/qga/commands.c
> @@ -45,35 +45,27 @@ void qmp_guest_ping(Error **err)
>      slog("guest-ping called");
>  }
> 
> -struct GuestAgentInfo *qmp_guest_info(Error **err)
> +static void qmp_command_info(QmpCommand *cmd, void *opaque)
>  {
> -    GuestAgentInfo *info = g_malloc0(sizeof(GuestAgentInfo));
> +    GuestAgentInfo *info = opaque;
>      GuestAgentCommandInfo *cmd_info;
>      GuestAgentCommandInfoList *cmd_info_list;
> -    char **cmd_list_head, **cmd_list;
> -
> -    info->version = g_strdup(QEMU_VERSION);
> -
> -    cmd_list_head = cmd_list = qmp_get_command_list();
> -    if (*cmd_list_head == NULL) {
> -        goto out;
> -    }
> 
> -    while (*cmd_list) {
> -        cmd_info = g_malloc0(sizeof(GuestAgentCommandInfo));
> -        cmd_info->name = g_strdup(*cmd_list);
> -        cmd_info->enabled = qmp_command_is_enabled(cmd_info->name);
> +    cmd_info = g_malloc0(sizeof(GuestAgentCommandInfo));
> +    cmd_info->name = g_strdup(cmd->name);
> +    cmd_info->enabled = qmp_command_is_enabled(cmd);
> 
> -        cmd_info_list = g_malloc0(sizeof(GuestAgentCommandInfoList));
> -        cmd_info_list->value = cmd_info;
> -        cmd_info_list->next = info->supported_commands;
> -        info->supported_commands = cmd_info_list;
> +    cmd_info_list = g_malloc0(sizeof(GuestAgentCommandInfoList));
> +    cmd_info_list->value = cmd_info;
> +    cmd_info_list->next = info->supported_commands;
> +    info->supported_commands = cmd_info_list;
> +}
> 
> -        g_free(*cmd_list);
> -        cmd_list++;
> -    }
> +struct GuestAgentInfo *qmp_guest_info(Error **err)
> +{
> +    GuestAgentInfo *info = g_malloc0(sizeof(GuestAgentInfo));
> 
> -out:
> -    g_free(cmd_list_head);
> +    info->version = g_strdup(QEMU_VERSION);
> +    qmp_for_each_command(qmp_command_info, info);
>      return info;
>  }
> diff --git a/qga/main.c b/qga/main.c
> index 6c746c8..ff2ee03 100644
> --- a/qga/main.c
> +++ b/qga/main.c
> @@ -347,48 +347,34 @@ static gint ga_strcmp(gconstpointer str1, gconstpointer str2)
>  }
> 
>  /* disable commands that aren't safe for fsfreeze */
> -static void ga_disable_non_whitelisted(void)
> +static void ga_disable_non_whitelisted(QmpCommand *cmd, void *opaque)
>  {
> -    char **list_head, **list;
>      bool whitelisted;
>      int i;
> 
> -    list_head = list = qmp_get_command_list();
> -    while (*list != NULL) {
> -        whitelisted = false;
> -        i = 0;
> -        while (ga_freeze_whitelist[i] != NULL) {
> -            if (strcmp(*list, ga_freeze_whitelist[i]) == 0) {
> -                whitelisted = true;
> -            }
> -            i++;
> -        }
> -        if (!whitelisted) {
> -            g_debug("disabling command: %s", *list);
> -            qmp_disable_command(*list);
> +    whitelisted = false;
> +    i = 0;
> +    while (ga_freeze_whitelist[i] != NULL) {
> +        if (strcmp(cmd->name, ga_freeze_whitelist[i]) == 0) {
> +            whitelisted = true;
>          }
> -        g_free(*list);
> -        list++;
> +        i++;
> +    }
> +    if (!whitelisted) {
> +        g_debug("disabling command: %s", cmd->name);
> +        qmp_disable_command(cmd->name);
>      }
> -    g_free(list_head);
>  }
> 
>  /* [re-]enable all commands, except those explicitly blacklisted by user */
> -static void ga_enable_non_blacklisted(GList *blacklist)
> +static void ga_enable_non_blacklisted(QmpCommand *cmd, void *opaque)
>  {
> -    char **list_head, **list;
> -
> -    list_head = list = qmp_get_command_list();
> -    while (*list != NULL) {
> -        if (g_list_find_custom(blacklist, *list, ga_strcmp) == NULL &&
> -            !qmp_command_is_enabled(*list)) {
> -            g_debug("enabling command: %s", *list);
> -            qmp_enable_command(*list);
> -        }
> -        g_free(*list);
> -        list++;
> +    GList *blacklist = opaque;
> +    if (g_list_find_custom(blacklist, cmd->name, ga_strcmp) == NULL &&
> +        !cmd->enabled) {

qmp_command_is_enabled(cmd)

I also agree with Eric's comments about using an accessor for cmd->name to
we can continue treating QmpCommand as an opaque.

Other than that, looks good.