qemu-log: support simple pid substitution for logs

When debugging stuff that occurs over several forks it would be useful
not to keep overwriting the one logfile you've set-up. This allows a
simple %d to be included once in the logfile parameter which is
substituted with getpid().

As the test cases involve checking user output they need
g_test_trap_subprocess() support. As a result they are currently skipped
on Travis builds due to the older glib involved.
Signed-off-by: NAlex Bennée <alex.bennee@linaro.org>
Reviewed-by: NLeandro Dorileo <l@dorileo.org>
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Reviewed-by: NRichard Henderson  <rth@twiddle.net>
Message-Id: <1458052224-9316-10-git-send-email-alex.bennee@linaro.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

tests/test-logging.c

@@ -89,7 +89,37 @@ static void test_parse_zero_range(void)
     g_test_trap_assert_stdout("");
     g_test_trap_assert_stderr("*Failed to parse range in: 0x1000+0\n");
 }
-#endif
+
+/* As the only real failure from a bad log filename path spec is
+ * reporting to the user we have to use the g_test_trap_subprocess
+ * mechanism and check no errors reported on stderr.
+ */
+static void test_parse_path_subprocess(void)
+{
+    /* All these should work without issue */
+    qemu_set_log_filename("/tmp/qemu.log");
+    qemu_set_log_filename("/tmp/qemu-%d.log");
+    qemu_set_log_filename("/tmp/qemu.log.%d");
+}
+static void test_parse_path(void)
+{
+    g_test_trap_subprocess ("/logging/parse_path/subprocess", 0, 0);
+    g_test_trap_assert_passed();
+    g_test_trap_assert_stdout("");
+    g_test_trap_assert_stderr("");
+}
+static void test_parse_invalid_path_subprocess(void)
+{
+    qemu_set_log_filename("/tmp/qemu-%d%d.log");
+}
+static void test_parse_invalid_path(void)
+{
+    g_test_trap_subprocess ("/logging/parse_invalid_path/subprocess", 0, 0);
+    g_test_trap_assert_passed();
+    g_test_trap_assert_stdout("");
+    g_test_trap_assert_stderr("Bad logfile format: /tmp/qemu-%d%d.log\n");
+}
+#endif /* CONFIG_HAS_GLIB_SUBPROCESS_TESTS */
 
 int main(int argc, char **argv)
 {
@@ -101,6 +131,10 @@ int main(int argc, char **argv)
     g_test_add_func("/logging/parse_invalid_range", test_parse_invalid_range);
     g_test_add_func("/logging/parse_zero_range/subprocess", test_parse_zero_range_subprocess);
     g_test_add_func("/logging/parse_zero_range", test_parse_zero_range);
+    g_test_add_func("/logging/parse_path", test_parse_path);
+    g_test_add_func("/logging/parse_path/subprocess", test_parse_path_subprocess);
+    g_test_add_func("/logging/parse_invalid_path", test_parse_invalid_path);
+    g_test_add_func("/logging/parse_invalid_path/subprocess", test_parse_invalid_path_subprocess);
 #endif
 
     return g_test_run();

util/log.c

@@ -89,11 +89,28 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
         qemu_log_close();
     }
 }
-
+/*
+ * Allow the user to include %d in their logfile which will be
+ * substituted with the current PID. This is useful for debugging many
+ * nested linux-user tasks but will result in lots of logs.
+ */
 void qemu_set_log_filename(const char *filename)
 {
+    char *pidstr;
     g_free(logfilename);
+
+    pidstr = strstr(filename, "%");
+    if (pidstr) {
+        /* We only accept one %d, no other format strings */
+        if (pidstr[1] != 'd' || strchr(pidstr + 2, '%')) {
+            error_report("Bad logfile format: %s", filename);
+            logfilename = NULL;
+        } else {
+            logfilename = g_strdup_printf(filename, getpid());
+        }
+    } else {
         logfilename = g_strdup(filename);
+    }
     qemu_log_close();
     qemu_set_log(qemu_loglevel);
 }