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Date: Tue, 18 Mar 2014 16:57:48 +0200
From: "Michael S. Tsirkin" <mst@redhat.com>
Message-ID: <20140318145748.GA28344@redhat.com>
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Subject: Re: [Qemu-devel] small memory leak due to MachineClass rework
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To: Christian Borntraeger <borntraeger@de.ibm.com>
Cc: "qemu-devel@nongnu.org" <qemu-devel@nongnu.org>, Andreas =?iso-8859-1?Q?F=E4rber?= <afaerber@suse.de>, Marcel Apfelbaum <marcel.a@redhat.com>

On Mon, Mar 17, 2014 at 09:56:45PM +0100, Christian Borntraeger wrote:
> Marcel,
> 
> after 
> 
> commit 261747f176f6 (vl: Use MachineClass instead of global QEMUMachine list) valgrind complains about the following:
> 
> ==54082== 57 bytes in 3 blocks are definitely lost in loss record 365 of 729
> ==54082==    at 0x4031AFE: malloc (vg_replace_malloc.c:292)
> ==54082==    by 0x4145569: g_malloc (in /usr/lib64/libglib-2.0.so.0.3400.2)
> ==54082==    by 0x415F9E9: g_strconcat (in /usr/lib64/libglib-2.0.so.0.3400.2)
> ==54082==    by 0x80157FE7: qemu_register_machine (vl.c:1597)
> ==54082==    by 0x80208E6B: module_call_init (module.c:105)
> ==54082==    by 0x80013B91: main (vl.c:3000)
> 
> Turns out that valgrind is right. We simply forget the memory that g_strconcat has allocated.
> This fixes the small leak, but I have to cast away the constness of .name.
> Any better ideas?
> 
> 
> diff --git a/vl.c b/vl.c
> index 03488b9..b06d186 100644
> --- a/vl.c
> +++ b/vl.c
> @@ -1594,13+1594,14 @@ static void machine_class_init(ObjectClass *oc, void *data)
>  int qemu_register_machine(QEMUMachine *m)
>  {
>      TypeInfo ti = {
>          .name       = g_strconcat(m->name, TYPE_MACHINE_SUFFIX, NULL),
>          .parent     = TYPE_MACHINE,
>          .class_init = machine_class_init,
>          .class_data = (void *)m,
>      };
>  
>      type_register(&ti);
> +    g_free((gpointer) ti.name);
>  
>      return 0;
>  }


How about:

 int qemu_register_machine(QEMUMachine *m)
 {
+  char *name = g_strconcat(m->name, TYPE_MACHINE_SUFFIX, NULL);
   TypeInfo ti = {
-        .name       = g_strconcat(m->name, TYPE_MACHINE_SUFFIX, NULL),
+        .name       = name,
         .parent     = TYPE_MACHINE,
         .class_init = machine_class_init,
         .class_data = (void *)m,
     };
 
     type_register(&ti);
+    g_free(name);
 
     return 0;
 }