qemu: Make virFileFindHugeTLBFS fault tolerant

Since commit be0782e1 we are parsing /proc/meminfo to find out the
default huge page size. However, if the host we are running at does
not support any huge pages (e.g. CONFIG_HUGETLB_PAGE is turned off),
we will not successfully parse the meminfo file and hence the whole
qemu driver init process fails. Moreover, the default huge page size
is needed if and only if there's at least one hugetlbfs mount point.
So the fix consists of moving the virFileGetDefaultHugepageSize
function call after the first hugetlbfs mount point is found.

With this fix, we fail to start with one or more hugetlbfs mounts and
malformed meminfo file, but that's expected (how can one mount
hugetlbfs without kernel supporting huge pages?). Workaround in that
case is to umount all the hugetlbfs mounts.
Reported-by: NJim Fehlig <jfehlig@suse.com>
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

src/util/virfile.c

@@ -2990,10 +2990,7 @@ virFileFindHugeTLBFS(virHugeTLBFSPtr *ret_fs,
     char mntbuf[1024];
     virHugeTLBFSPtr fs = NULL;
     size_t nfs = 0;
-    unsigned long long default_hugepagesz;
-
-    if (virFileGetDefaultHugepageSize(&default_hugepagesz) < 0)
-        goto cleanup;
+    unsigned long long default_hugepagesz = 0;
 
     if (!(f = setmntent(PROC_MOUNTS, "r"))) {
         virReportSystemError(errno,
@@ -3019,6 +3016,10 @@ virFileFindHugeTLBFS(virHugeTLBFSPtr *ret_fs,
         if (virFileGetHugepageSize(tmp->mnt_dir, &tmp->size) < 0)
             goto cleanup;
 
+        if (!default_hugepagesz &&
+            virFileGetDefaultHugepageSize(&default_hugepagesz) < 0)
+            goto cleanup;
+
         tmp->deflt = tmp->size == default_hugepagesz;
     }