[Xen-devel] [PATCH v2 01/11] tools/libs/toollog: Provide a default logger

[Ian Jackson <ian.jackson@xxxxxxxxxxxxx>]

This is most conveniently done like this because xtl_logger_stdio.c
knows how to provide a static logger without doing any memory
allocations.  That's useful because it can't fail.

Add the new symbol to the map file and bump the minor version
accordingly.

Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
---
v2: New in this version of the series
---
 tools/libs/toollog/Makefile             |  2 +-
 tools/libs/toollog/include/xentoollog.h |  5 +++++
 tools/libs/toollog/libxentoollog.map    |  5 +++++
 tools/libs/toollog/xtl_logger_stdio.c   | 26 ++++++++++++++++++++++++++
 4 files changed, 37 insertions(+), 1 deletion(-)

diff --git a/tools/libs/toollog/Makefile b/tools/libs/toollog/Makefile
index 8aae2c8f53..3aa0997757 100644
--- a/tools/libs/toollog/Makefile
+++ b/tools/libs/toollog/Makefile
@@ -2,7 +2,7 @@ XEN_ROOT = $(CURDIR)/../../..
 include $(XEN_ROOT)/tools/Rules.mk
 
 MAJOR  = 1
-MINOR  = 0
+MINOR  = 1
 SHLIB_LDFLAGS += -Wl,--version-script=libxentoollog.map
 
 CFLAGS += -Werror -Wmissing-prototypes
diff --git a/tools/libs/toollog/include/xentoollog.h 
b/tools/libs/toollog/include/xentoollog.h
index 76f17fe125..942eb76169 100644
--- a/tools/libs/toollog/include/xentoollog.h
+++ b/tools/libs/toollog/include/xentoollog.h
@@ -86,6 +86,11 @@ void 
xtl_stdiostream_adjust_flags(xentoollog_logger_stdiostream*,
 void xtl_logger_destroy(struct xentoollog_logger *logger /* 0 is ok */);
 
 
+xentoollog_logger_stdiostream *xtl_defaultlogger_stdiostream(void);
+  /* Returns pointer to a static global logger which writes to stderr.
+   * Reconfiguring it is permitted but destroying it is forbidden.
+   * This function cannot fail. */
+
 /*---------- facilities for generating log messages ----------*/
 
 void xtl_logv(struct xentoollog_logger *logger,
diff --git a/tools/libs/toollog/libxentoollog.map 
b/tools/libs/toollog/libxentoollog.map
index c183cf555d..00eaacaeaf 100644
--- a/tools/libs/toollog/libxentoollog.map
+++ b/tools/libs/toollog/libxentoollog.map
@@ -10,3 +10,8 @@ VERS_1.0 {
                xtl_stdiostream_set_minlevel;
        local: *; /* Do not expose anything by default */
 };
+
+VERS_1.1 {
+       global:
+               xtl_defaultlogger_stdiostream;
+} VERS_1.0;
diff --git a/tools/libs/toollog/xtl_logger_stdio.c 
b/tools/libs/toollog/xtl_logger_stdio.c
index 52dfbf51e3..07fe355626 100644
--- a/tools/libs/toollog/xtl_logger_stdio.c
+++ b/tools/libs/toollog/xtl_logger_stdio.c
@@ -28,6 +28,7 @@
 #include <stdlib.h>
 #include <errno.h>
 #include <stdbool.h>
+#include <pthread.h>
 
 struct xentoollog_logger_stdiostream {
     xentoollog_logger vtable;
@@ -191,6 +192,31 @@ xentoollog_logger_stdiostream *xtl_createlogger_stdiostream
     return XTL_NEW_LOGGER(stdiostream, newlogger);
 }
 
+xentoollog_logger_stdiostream *xtl_defaultlogger_stdiostream(void) {
+    static xentoollog_logger_stdiostream deflogger = {
+        .vtable = {
+            .vmessage = stdiostream_vmessage,
+            .progress = stdiostream_progress,
+            .destroy  = 0, /* no-one should destroy this */
+        },
+        .min_level = XTL_PROGRESS,
+        /* for other fields except .f, 0 is good */
+    };
+
+    /*
+     * Unfortunately, stderr is not a `constant expression', so we
+     * can't handle it in the initialisation.  Also we can't do a
+     * lockless assignment, even of the identical value, without
+     * violating threading rules.  Nnng.
+     */
+    static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
+    pthread_mutex_lock(&mutex);
+    deflogger.f = stderr;
+    pthread_mutex_unlock(&mutex);
+
+    return &deflogger;
+};
+
 /*
  * Local variables:
  * mode: C
-- 
2.11.0


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