1 files changed, 76 insertions, 24 deletions

diff --git a/util/log.c b/util/log.c
index 1ca13059ee..867264da8d 100644
--- a/util/log.c
+++ b/util/log.c
@@ -24,9 +24,11 @@
 #include "qapi/error.h"
 #include "qemu/cutils.h"
 #include "trace/control.h"
+#include "qemu/thread.h"
 
 static char *logfilename;
-FILE *qemu_logfile;
+static QemuMutex qemu_logfile_mutex;
+QemuLogFile *qemu_logfile;
 int qemu_loglevel;
 static int log_append = 0;
 static GArray *debug_regions;
@@ -35,10 +37,14 @@ static GArray *debug_regions;
 int qemu_log(const char *fmt, ...)
 {
     int ret = 0;
-    if (qemu_logfile) {
+    QemuLogFile *logfile;
+
+    rcu_read_lock();
+    logfile = atomic_rcu_read(&qemu_logfile);
+    if (logfile) {
         va_list ap;
         va_start(ap, fmt);
-        ret = vfprintf(qemu_logfile, fmt, ap);
+        ret = vfprintf(logfile->fd, fmt, ap);
         va_end(ap);
 
         /* Don't pass back error results.  */
@@ -46,57 +52,91 @@ int qemu_log(const char *fmt, ...)
             ret = 0;
         }
     }
+    rcu_read_unlock();
     return ret;
 }
 
+static void __attribute__((__constructor__)) qemu_logfile_init(void)
+{
+    qemu_mutex_init(&qemu_logfile_mutex);
+}
+
+static void qemu_logfile_free(QemuLogFile *logfile)
+{
+    g_assert(logfile);
+
+    if (logfile->fd != stderr) {
+        fclose(logfile->fd);
+    }
+    g_free(logfile);
+}
+
 static bool log_uses_own_buffers;
 
 /* enable or disable low levels log */
 void qemu_set_log(int log_flags)
 {
+    bool need_to_open_file = false;
+    QemuLogFile *logfile;
+
     qemu_loglevel = log_flags;
 #ifdef CONFIG_TRACE_LOG
     qemu_loglevel |= LOG_TRACE;
 #endif
-    if (!qemu_logfile &&
-        (is_daemonized() ? logfilename != NULL : qemu_loglevel)) {
+    /*
+     * In all cases we only log if qemu_loglevel is set.
+     * Also:
+     *   If not daemonized we will always log either to stderr
+     *     or to a file (if there is a logfilename).
+     *   If we are daemonized,
+     *     we will only log if there is a logfilename.
+     */
+    if (qemu_loglevel && (!is_daemonized() || logfilename)) {
+        need_to_open_file = true;
+    }
+    qemu_mutex_lock(&qemu_logfile_mutex);
+    if (qemu_logfile && !need_to_open_file) {
+        logfile = qemu_logfile;
+        atomic_rcu_set(&qemu_logfile, NULL);
+        call_rcu(logfile, qemu_logfile_free, rcu);
+    } else if (!qemu_logfile && need_to_open_file) {
+        logfile = g_new0(QemuLogFile, 1);
         if (logfilename) {
-            qemu_logfile = fopen(logfilename, log_append ? "a" : "w");
-            if (!qemu_logfile) {
+            logfile->fd = fopen(logfilename, log_append ? "a" : "w");
+            if (!logfile->fd) {
+                g_free(logfile);
                 perror(logfilename);
                 _exit(1);
             }
             /* In case we are a daemon redirect stderr to logfile */
             if (is_daemonized()) {
-                dup2(fileno(qemu_logfile), STDERR_FILENO);
-                fclose(qemu_logfile);
+                dup2(fileno(logfile->fd), STDERR_FILENO);
+                fclose(logfile->fd);
                 /* This will skip closing logfile in qemu_log_close() */
-                qemu_logfile = stderr;
+                logfile->fd = stderr;
             }
         } else {
             /* Default to stderr if no log file specified */
             assert(!is_daemonized());
-            qemu_logfile = stderr;
+            logfile->fd = stderr;
         }
         /* must avoid mmap() usage of glibc by setting a buffer "by hand" */
         if (log_uses_own_buffers) {
             static char logfile_buf[4096];
 
-            setvbuf(qemu_logfile, logfile_buf, _IOLBF, sizeof(logfile_buf));
+            setvbuf(logfile->fd, logfile_buf, _IOLBF, sizeof(logfile_buf));
         } else {
 #if defined(_WIN32)
             /* Win32 doesn't support line-buffering, so use unbuffered output. */
-            setvbuf(qemu_logfile, NULL, _IONBF, 0);
+            setvbuf(logfile->fd, NULL, _IONBF, 0);
 #else
-            setvbuf(qemu_logfile, NULL, _IOLBF, 0);
+            setvbuf(logfile->fd, NULL, _IOLBF, 0);
 #endif
             log_append = 1;
         }
+        atomic_rcu_set(&qemu_logfile, logfile);
     }
-    if (qemu_logfile &&
-        (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) {
-        qemu_log_close();
-    }
+    qemu_mutex_unlock(&qemu_logfile_mutex);
 }
 
 void qemu_log_needs_buffers(void)
@@ -113,6 +153,7 @@ void qemu_set_log_filename(const char *filename, Error **errp)
 {
     char *pidstr;
     g_free(logfilename);
+    logfilename = NULL;
 
     pidstr = strstr(filename, "%");
     if (pidstr) {
@@ -224,18 +265,29 @@ out:
 /* fflush() the log file */
 void qemu_log_flush(void)
 {
-    fflush(qemu_logfile);
+    QemuLogFile *logfile;
+
+    rcu_read_lock();
+    logfile = atomic_rcu_read(&qemu_logfile);
+    if (logfile) {
+        fflush(logfile->fd);
+    }
+    rcu_read_unlock();
 }
 
 /* Close the log file */
 void qemu_log_close(void)
 {
-    if (qemu_logfile) {
-        if (qemu_logfile != stderr) {
-            fclose(qemu_logfile);
-        }
-        qemu_logfile = NULL;
+    QemuLogFile *logfile;
+
+    qemu_mutex_lock(&qemu_logfile_mutex);
+    logfile = qemu_logfile;
+
+    if (logfile) {
+        atomic_rcu_set(&qemu_logfile, NULL);
+        call_rcu(logfile, qemu_logfile_free, rcu);
     }
+    qemu_mutex_unlock(&qemu_logfile_mutex);
 }
 
 const QEMULogItem qemu_log_items[] = {