[libvirt] [PATCHv3] Fix Memory Leak in virQEMUCapsInitGuestFromBinary()

[Nehal J Wani]

While running qemucaps2xmltest, it was found that valgrind pointed out
the following memory leaks:

==29896== 0 bytes in 1 blocks are definitely lost in loss record 1 of 65
==29896==    at 0x4A0577B: calloc (vg_replace_malloc.c:593)
==29896==    by 0x4C6B45E: virAllocN (viralloc.c:191)
==29896==    by 0x4232A9: virQEMUCapsGetMachineTypesCaps (qemu_capabilities.c:1999)
==29896==    by 0x4234E7: virQEMUCapsInitGuestFromBinary (qemu_capabilities.c:789)
==29896==    by 0x41F10B: testQemuCapsXML (qemucaps2xmltest.c:118)
==29896==    by 0x41FFD1: virtTestRun (testutils.c:201)
==29896==    by 0x41EE7A: mymain (qemucaps2xmltest.c:203)
==29896==    by 0x42074D: virtTestMain (testutils.c:789)
==29896==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)
==29896==
==29896== 0 bytes in 1 blocks are definitely lost in loss record 2 of 65
==29896==    at 0x4A0577B: calloc (vg_replace_malloc.c:593)
==29896==    by 0x4C6B45E: virAllocN (viralloc.c:191)
==29896==    by 0x4232A9: virQEMUCapsGetMachineTypesCaps (qemu_capabilities.c:1999)
==29896==    by 0x4234E7: virQEMUCapsInitGuestFromBinary (qemu_capabilities.c:789)
==29896==    by 0x41F10B: testQemuCapsXML (qemucaps2xmltest.c:118)
==29896==    by 0x41FFD1: virtTestRun (testutils.c:201)
==29896==    by 0x41EEA3: mymain (qemucaps2xmltest.c:204)
==29896==    by 0x42074D: virtTestMain (testutils.c:789)
==29896==    by 0x3E6CE1ED1C: (below main) (libc-start.c:226)

---
 Based on Daniel's comments.
 v2: https://www.redhat.com/archives/libvir-list/2014-March/msg01672.html
 v1: https://www.redhat.com/archives/libvir-list/2014-March/msg01667.html

 src/qemu/qemu_capabilities.c |    6 ++++--
 1 files changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/qemu/qemu_capabilities.c b/src/qemu/qemu_capabilities.c
index 7673592..e4c1cbd 100644
--- a/src/qemu/qemu_capabilities.c
+++ b/src/qemu/qemu_capabilities.c
@@ -1996,10 +1996,12 @@ int virQEMUCapsGetMachineTypesCaps(virQEMUCapsPtr qemuCaps,
 
     *nmachines = 0;
     *machines = NULL;
-    if (VIR_ALLOC_N(*machines, qemuCaps->nmachineTypes) < 0)
-        goto error;
     *nmachines = qemuCaps->nmachineTypes;
 
+    if (*nmachines &&
+        VIR_ALLOC_N(*machines, qemuCaps->nmachineTypes) < 0)
+        goto error;
+
     for (i = 0; i < qemuCaps->nmachineTypes; i++) {
         virCapsGuestMachinePtr mach;
         if (VIR_ALLOC(mach) < 0)
-- 
1.7.1