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: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Leandro Dorileo <l@dorileo.org>
Reviewed-by: Aurelien Jarno <aurelien@aurel32.net>
Reviewed-by: Richard Henderson  <rth@twiddle.net>
Message-Id: <1458052224-9316-10-git-send-email-alex.bennee@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 19 insertions, 2 deletions

diff --git a/util/log.c b/util/log.c
index 671b6174e4..b219081e91 100644
--- a/util/log.c
+++ b/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);
-    logfilename = g_strdup(filename);
+
+    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);
 }