log: actually do substring matches with fnmatch

Historically we matched log filters with strstr(), and when switching to
fnmatch in cbb0fd3cfd, it was stated that
we would continue to match substrings, with "foo" being equivalent to
"*foo*". Unfortuntely I forget to provide the code to actually make that
happen. This fixes it to prepend and append "*". We don't bother to
check if the pattern already has a leading/trailing '*', because
"**foo**" will match the same as "*foo*".

Reviewed-by: Erik Skultety <eskultet@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

src/util/virlog.c

@@ -1409,6 +1409,7 @@ virLogFilterNew(const char *match,
 {
     virLogFilterPtr ret = NULL;
     char *mdup = NULL;
+    size_t mlen = strlen(match);
 
     virCheckFlags(VIR_LOG_STACK_TRACE, NULL);
 
@@ -1418,9 +1419,16 @@ virLogFilterNew(const char *match,
         return NULL;
     }
 
-    if (VIR_STRDUP_QUIET(mdup, match) < 0)
+    /* We must treat 'foo' as equiv to '*foo*' for fnmatch
+     * todo substring matches, so add 2 extra bytes
+     */
+    if (VIR_ALLOC_N_QUIET(mdup, mlen + 3) < 0)
         return NULL;
 
+    mdup[0] = '*';
+    memcpy(mdup + 1, match, mlen);
+    mdup[mlen + 1] = '*';
+
     if (VIR_ALLOC_QUIET(ret) < 0) {
         VIR_FREE(mdup);
         return NULL;