[Qemu-devel] [PATCH 1/1] log: fix hanged connect from virt-manager to libvirt

[Denis V. Lunev]

libvirt in this case spawns
  /usr/bin/qemu-system-x86_64 -S -no-user-config -nodefaults -nographic
    -M none
    -qmp unix:/var/lib/libvirt/qemu/capabilities.monitor.sock,server,nowait
    -pidfile /var/lib/libvirt/qemu/capabilities.pidfile -daemonize
and with CONFIG_TRACE_LOG this process hangs as stderr becomes redirected
to terminal (qemu_logfile == stderr). We do not have redirection to
/dev/null in this case which is necessary.

Broken by:
    commit 96c33a4523ee1abe382ce4ff3e82b90ba78aa186
    Author: Dimitris Aragiorgis <address@hidden>
    Date:   Thu Feb 18 13:38:38 2016 +0200

    log: Redirect stderr to logfile if deamonized

We should also take into account log filename change in runtime through
QMP/HMP, when the log could be even closed. In this case stderr should
be tweaked accordingly.

Signed-off-by: Denis V. Lunev <address@hidden>
CC: Dimitris Aragiorgis <address@hidden>
CC: Paolo Bonzini <address@hidden>
CC: Vladimir Sementsov-Ogievskiy <address@hidden>
---
 include/qemu/log.h | 4 ++++
 os-posix.c         | 2 +-
 util/log.c         | 7 ++-----
 3 files changed, 7 insertions(+), 6 deletions(-)

diff --git a/include/qemu/log.h b/include/qemu/log.h
index dda65fd..8083f82 100644
--- a/include/qemu/log.h
+++ b/include/qemu/log.h
@@ -92,6 +92,10 @@ static inline void qemu_log_close(void)
         }
         qemu_logfile = NULL;
     }
+
+    if (is_daemonized()) {
+        dup2(STDOUT_FILENO, STDERR_FILENO); /* dup /dev/null to stderr */
+    }
 }
 
 /* define log items */
diff --git a/os-posix.c b/os-posix.c
index 92fa3ba..d4b2a91 100644
--- a/os-posix.c
+++ b/os-posix.c
@@ -277,7 +277,7 @@ void os_setup_post(void)
         dup2(fd, 0);
         dup2(fd, 1);
         /* In case -D is given do not redirect stderr to /dev/null */
-        if (!qemu_logfile) {
+        if (!qemu_logfile || qemu_logfile == stderr) {
             dup2(fd, 2);
         }
 
diff --git a/util/log.c b/util/log.c
index a7ddc7e..a06aa14 100644
--- a/util/log.c
+++ b/util/log.c
@@ -56,7 +56,7 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
 #ifdef CONFIG_TRACE_LOG
     qemu_loglevel |= LOG_TRACE;
 #endif
-    if ((qemu_loglevel || is_daemonized()) && !qemu_logfile) {
+    if (qemu_loglevel && !qemu_logfile) {
         if (logfilename) {
             qemu_logfile = fopen(logfilename, log_append ? "a" : "w");
             if (!qemu_logfile) {
@@ -66,9 +66,6 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
             /* In case we are a daemon redirect stderr to logfile */
             if (is_daemonized()) {
                 dup2(fileno(qemu_logfile), STDERR_FILENO);
-                fclose(qemu_logfile);
-                /* This will skip closing logfile in qemu_log_close() */
-                qemu_logfile = stderr;
             }
         } else {
             /* Default to stderr if no log file specified */
@@ -89,7 +86,7 @@ void do_qemu_set_log(int log_flags, bool use_own_buffers)
             log_append = 1;
         }
     }
-    if (!qemu_loglevel && !is_daemonized() && qemu_logfile) {
+    if (!qemu_loglevel && qemu_logfile) {
         qemu_log_close();
     }
 }
-- 
2.5.0