diff mbox series

[1/4] Add a mutex to guarantee single writer to qemu_logfile handle.

Message ID 20191107142613.2379-2-robert.foley@linaro.org
State New
Headers show
Series Make the qemu_logfile handle thread safe. | expand

Commit Message

Robert Foley Nov. 7, 2019, 2:26 p.m. UTC 
This is being added in preparation for using RCU with the logfile handle.
Also added qemu_logfile_init() for initializing the logfile mutex.

Signed-off-by: Robert Foley <robert.foley@linaro.org>

---
 util/log.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

-- 
2.17.1

Comments

Alex Bennée Nov. 7, 2019, 4:53 p.m. UTC | #1 
Robert Foley <robert.foley@linaro.org> writes:

> This is being added in preparation for using RCU with the logfile handle.

> Also added qemu_logfile_init() for initializing the logfile mutex.

>

> Signed-off-by: Robert Foley <robert.foley@linaro.org>

> ---

>  util/log.c | 23 +++++++++++++++++++++++

>  1 file changed, 23 insertions(+)

>

> diff --git a/util/log.c b/util/log.c

> index 1ca13059ee..dff2f98c8c 100644

> --- a/util/log.c

> +++ b/util/log.c

> @@ -24,8 +24,11 @@

>  #include "qapi/error.h"

>  #include "qemu/cutils.h"

>  #include "trace/control.h"

> +#include "qemu/thread.h"

>

>  static char *logfilename;

> +static bool qemu_logfile_initialized;

> +static QemuMutex qemu_logfile_mutex;

>  FILE *qemu_logfile;

>  int qemu_loglevel;

>  static int log_append = 0;

> @@ -49,6 +52,14 @@ int qemu_log(const char *fmt, ...)

>      return ret;

>  }

>

> +static void qemu_logfile_init(void)

> +{

> +    if (!qemu_logfile_initialized) {

> +        qemu_mutex_init(&qemu_logfile_mutex);

> +        qemu_logfile_initialized = true;

> +    }

> +}

> +

>  static bool log_uses_own_buffers;

>

>  /* enable or disable low levels log */

> @@ -58,6 +69,12 @@ void qemu_set_log(int log_flags)

>  #ifdef CONFIG_TRACE_LOG

>      qemu_loglevel |= LOG_TRACE;

>  #endif

> +

> +    /* Is there a better place to call this to init the logfile subsystem? */

> +    if (!qemu_logfile_initialized) {

> +        qemu_logfile_init();

> +    }


It wouldn't be the worst thing in the world to expose:

  qemu_logfile_init()

and make vl.c and main.c call it before the setup. Then you can drop the
flag or even just g_assert(qemu_log_mutex_initialised) in qemu_set_log
and qemu_set_logfile.

In fact you could just use:

  static void __attribute__((__constructor__)) qemu_logfile_init(void)

and make the compiler do it for you.

> +    qemu_mutex_lock(&qemu_logfile_mutex);

>      if (!qemu_logfile &&

>          (is_daemonized() ? logfilename != NULL : qemu_loglevel)) {

>          if (logfilename) {

> @@ -93,6 +110,7 @@ void qemu_set_log(int log_flags)

>              log_append = 1;

>          }

>      }

> +    qemu_mutex_unlock(&qemu_logfile_mutex);

>      if (qemu_logfile &&

>          (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) {

>          qemu_log_close();

> @@ -114,6 +132,11 @@ void qemu_set_log_filename(const char *filename, Error **errp)

>      char *pidstr;

>      g_free(logfilename);

>

> +    /* Is there a better place to call this to init the logfile subsystem? */

> +    if (!qemu_logfile_initialized) {

> +        qemu_logfile_init();

> +    }

> +

>      pidstr = strstr(filename, "%");

>      if (pidstr) {

>          /* We only accept one %d, no other format strings */



--
Alex Bennée
Robert Foley Nov. 7, 2019, 9:54 p.m. UTC | #2 
On Thu, 7 Nov 2019 at 11:53, Alex Bennée <alex.bennee@linaro.org> wrote:
>

> It wouldn't be the worst thing in the world to expose:

>

>   qemu_logfile_init()

>

> and make vl.c and main.c call it before the setup. Then you can drop the

> flag or even just g_assert(qemu_log_mutex_initialised) in qemu_set_log

> and qemu_set_logfile.

>

> In fact you could just use:

>

>   static void __attribute__((__constructor__)) qemu_logfile_init(void)

>

> and make the compiler do it for you.


All good ideas.  Will make the changes.
I agree, it is much cleaner to call init this way (constructor).  We
can assert that qemu_log_mutex.initialized on use of the mutex
(qemu_set_log and qemu_set_logfile).  Taking that one step further, we
could add simple helper functions for
qemu_logfile_mutex_lock()/unlock(), which g_assert() on
mutex.initialized first before lock/unlock.

Thanks,
-Rob
On Thu, 7 Nov 2019 at 11:53, Alex Bennée <alex.bennee@linaro.org> wrote:
>

>

> Robert Foley <robert.foley@linaro.org> writes:

>

> > This is being added in preparation for using RCU with the logfile handle.

> > Also added qemu_logfile_init() for initializing the logfile mutex.

> >

> > Signed-off-by: Robert Foley <robert.foley@linaro.org>

> > ---

> >  util/log.c | 23 +++++++++++++++++++++++

> >  1 file changed, 23 insertions(+)

> >

> > diff --git a/util/log.c b/util/log.c

> > index 1ca13059ee..dff2f98c8c 100644

> > --- a/util/log.c

> > +++ b/util/log.c

> > @@ -24,8 +24,11 @@

> >  #include "qapi/error.h"

> >  #include "qemu/cutils.h"

> >  #include "trace/control.h"

> > +#include "qemu/thread.h"

> >

> >  static char *logfilename;

> > +static bool qemu_logfile_initialized;

> > +static QemuMutex qemu_logfile_mutex;

> >  FILE *qemu_logfile;

> >  int qemu_loglevel;

> >  static int log_append = 0;

> > @@ -49,6 +52,14 @@ int qemu_log(const char *fmt, ...)

> >      return ret;

> >  }

> >

> > +static void qemu_logfile_init(void)

> > +{

> > +    if (!qemu_logfile_initialized) {

> > +        qemu_mutex_init(&qemu_logfile_mutex);

> > +        qemu_logfile_initialized = true;

> > +    }

> > +}

> > +

> >  static bool log_uses_own_buffers;

> >

> >  /* enable or disable low levels log */

> > @@ -58,6 +69,12 @@ void qemu_set_log(int log_flags)

> >  #ifdef CONFIG_TRACE_LOG

> >      qemu_loglevel |= LOG_TRACE;

> >  #endif

> > +

> > +    /* Is there a better place to call this to init the logfile subsystem? */

> > +    if (!qemu_logfile_initialized) {

> > +        qemu_logfile_init();

> > +    }

>

> It wouldn't be the worst thing in the world to expose:

>

>   qemu_logfile_init()

>

> and make vl.c and main.c call it before the setup. Then you can drop the

> flag or even just g_assert(qemu_log_mutex_initialised) in qemu_set_log

> and qemu_set_logfile.

>

> In fact you could just use:

>

>   static void __attribute__((__constructor__)) qemu_logfile_init(void)

>

> and make the compiler do it for you.

>

> > +    qemu_mutex_lock(&qemu_logfile_mutex);

> >      if (!qemu_logfile &&

> >          (is_daemonized() ? logfilename != NULL : qemu_loglevel)) {

> >          if (logfilename) {

> > @@ -93,6 +110,7 @@ void qemu_set_log(int log_flags)

> >              log_append = 1;

> >          }

> >      }

> > +    qemu_mutex_unlock(&qemu_logfile_mutex);

> >      if (qemu_logfile &&

> >          (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) {

> >          qemu_log_close();

> > @@ -114,6 +132,11 @@ void qemu_set_log_filename(const char *filename, Error **errp)

> >      char *pidstr;

> >      g_free(logfilename);

> >

> > +    /* Is there a better place to call this to init the logfile subsystem? */

> > +    if (!qemu_logfile_initialized) {

> > +        qemu_logfile_init();

> > +    }

> > +

> >      pidstr = strstr(filename, "%");

> >      if (pidstr) {

> >          /* We only accept one %d, no other format strings */

>

>

> --

> Alex Bennée
diff mbox series

Patch

diff --git a/util/log.c b/util/log.c
index 1ca13059ee..dff2f98c8c 100644
--- a/util/log.c
+++ b/util/log.c
@@ -24,8 +24,11 @@ 
 #include "qapi/error.h"
 #include "qemu/cutils.h"
 #include "trace/control.h"
+#include "qemu/thread.h"
 
 static char *logfilename;
+static bool qemu_logfile_initialized;
+static QemuMutex qemu_logfile_mutex;
 FILE *qemu_logfile;
 int qemu_loglevel;
 static int log_append = 0;
@@ -49,6 +52,14 @@  int qemu_log(const char *fmt, ...)
     return ret;
 }
 
+static void qemu_logfile_init(void)
+{
+    if (!qemu_logfile_initialized) {
+        qemu_mutex_init(&qemu_logfile_mutex);
+        qemu_logfile_initialized = true;
+    }
+}
+
 static bool log_uses_own_buffers;
 
 /* enable or disable low levels log */
@@ -58,6 +69,12 @@  void qemu_set_log(int log_flags)
 #ifdef CONFIG_TRACE_LOG
     qemu_loglevel |= LOG_TRACE;
 #endif
+
+    /* Is there a better place to call this to init the logfile subsystem? */
+    if (!qemu_logfile_initialized) {
+        qemu_logfile_init();
+    }
+    qemu_mutex_lock(&qemu_logfile_mutex);
     if (!qemu_logfile &&
         (is_daemonized() ? logfilename != NULL : qemu_loglevel)) {
         if (logfilename) {
@@ -93,6 +110,7 @@  void qemu_set_log(int log_flags)
             log_append = 1;
         }
     }
+    qemu_mutex_unlock(&qemu_logfile_mutex);
     if (qemu_logfile &&
         (is_daemonized() ? logfilename == NULL : !qemu_loglevel)) {
         qemu_log_close();
@@ -114,6 +132,11 @@  void qemu_set_log_filename(const char *filename, Error **errp)
     char *pidstr;
     g_free(logfilename);
 
+    /* Is there a better place to call this to init the logfile subsystem? */
+    if (!qemu_logfile_initialized) {
+        qemu_logfile_init();
+    }
+
     pidstr = strstr(filename, "%");
     if (pidstr) {
         /* We only accept one %d, no other format strings */