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[libvirt] [PATCH] build: silence false positive clang report

clang complained that STREQ(group->controllers[i].mountPoint,...)  was
a NULL dereference when i==VIR_CGROUP_CONTROLLER_CPUSET, because it
assumes the worst about virCgroupPathOfController.  Marking the
argument const doesn't yet have an effect, per this clang bug:

So, we use sa_assert, which was designed to shut up false positives
from tools like clang.

* src/util/cgroup.c (virCgroupMakeGroup): Teach clang that there
is no NULL dereference.

I'm including enough context to show the STREQ that clang complained

And yes, I'm plowing through clang reports right now - there were
less than 20, so it seemed worth tackling before 0.8.8.

This one is a one-liner fix (tested by re-running clang and no longer
seeing a false positive, and sa_assert() is a no-op for gcc compilation),
but I'd rather get an ACK before pushing.

 src/util/cgroup.c |    3 +++
 1 files changed, 3 insertions(+), 0 deletions(-)

diff --git a/src/util/cgroup.c b/src/util/cgroup.c
index de1fd8e..47c4633 100644
--- a/src/util/cgroup.c
+++ b/src/util/cgroup.c
@@ -496,24 +496,27 @@ static int virCgroupMakeGroup(virCgroupPtr parent, virCgroupPtr group,

     VIR_DEBUG("Make group %s", group->path);
     for (i = 0 ; i < VIR_CGROUP_CONTROLLER_LAST ; i++) {
         char *path = NULL;

         /* Skip over controllers that aren't mounted */
         if (!group->controllers[i].mountPoint)

         rc = virCgroupPathOfController(group, i, "", &path);
         if (rc < 0)
             return rc;
+        /* As of Feb 2011, clang can't see that the above function
+         * call did not modify group. */
+        sa_assert(group->controllers[i].mountPoint);

         VIR_DEBUG("Make controller %s", path);
         if (access(path, F_OK) != 0) {
             if (!create ||
                 mkdir(path, 0755) < 0) {
                 rc = -errno;
             if (group->controllers[VIR_CGROUP_CONTROLLER_CPUSET].mountPoint != NULL &&
                 (i == VIR_CGROUP_CONTROLLER_CPUSET ||
                  STREQ(group->controllers[i].mountPoint, group->controllers[VIR_CGROUP_CONTROLLER_CPUSET].mountPoint))) {

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