qemu-devel
[Top][All Lists]
Advanced

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH] Extend qemu-ga's 'guest-info' command to expose


From: Mark Wu
Subject: Re: [Qemu-devel] [PATCH] Extend qemu-ga's 'guest-info' command to expose flag 'success-response'
Date: Wed, 25 Sep 2013 20:30:24 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130805 Thunderbird/17.0.8

Hi guys,

Thanks a lot for all your insightful comments. I will post a patch to resolve the O(n2) problem according to Michael's comments soon and rebase the 'success-response' on it.

Mark.

On 09/25/2013 08:34 AM, Luiz Capitulino wrote:
On Tue, 24 Sep 2013 16:07:29 -0500
Michael Roth <address@hidden> wrote:

+bool qmp_command_has_success_response(const char *name)
+{
+    QmpCommand *cmd;
+
+    QTAILQ_FOREACH(cmd, &qmp_commands, node) {
+        if (strcmp(cmd->name, name) == 0) {
+            return cmd->options != QCO_NO_SUCCESS_RESP;
cmd->options is a bitmask - it is feasible that we may add more QCO_NO_*
flags in the future, at which point inequality is NOT correct.  Rather,
you want:

return !(cmd->options & QCO_NO_SUCCESS_RESP);
Good catch! IIRC I added cmd->options myself and didn't catch this...

+++ b/qga/commands.c
@@ -63,6 +63,8 @@ struct GuestAgentInfo *qmp_guest_info(Error **err)
          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->success_response =
+            qmp_command_has_success_response(cmd_info->name);
This feels wasteful.  Why are we doing an O(n) lookup for BOTH
qmp_command_is_enabled AND qmp_command_has_success_response, in an O(n)
loop over command names?  That's O(n^2) in the number of commands.
Better would be getting a list of QmpCommand* instead of a list of
char*, and looking directly in each object, for O(n) computation of the
results.
Agreed, modifying qmp_get_command_list to return a list of QmpCommand
would be nicer. Rather than looking directly at the fields though I
think we should just fix up qmp_command_is_enabled() and friends to
take a QmpCommand arg instead of a char*. We already have
qmp_find_command to map char*->QmpCommand to support any cases where
we rely on cmd names.
I agree and I thought the same thing when I reviewed the patch, but
I didn't mind as Mark is just using what's already there.





reply via email to

[Prev in Thread] Current Thread [Next in Thread]