clock override: introduce getter API for lttng tools

Currently, the lttng session daemon reimplements its own copy of
struct lttng_trace_clock, which is pretty bad as ABI go.

Implement getter functions for each of the clock callback instead. This
refactoring needs to be introduced with a matching commit to use the new
ABI in LTTng tools.

Move the implementation of the clock frequency, uuid, name and
description default callbacks (for monotonic clock) to lttng-ust.

This allow to hide the previously exposed "lttng_trace_clock" public
symbol. Rename this internal symbol to lttng_ust_trace_clock for prefix
consistency. Rename struct lttng_trace_clock to struct
lttng_ust_trace_clock for similar reasons.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Change-Id: I55825f0c0f5372a68aaaf06fb8dbd256cf248f2c

diff --git a/include/lttng/ust-clock.h b/include/lttng/ust-clock.h
index 44b249b0651010553a97175453eb915ca26b6361..d608a933b8b26158351f7fb427903a4f324c9104 100644 (file)
--- a/include/lttng/ust-clock.h
+++ b/include/lttng/ust-clock.h
@@ -16,36 +16,47 @@
  * success.
  */
 
+typedef uint64_t (*lttng_ust_clock_read64_function)(void);
+typedef uint64_t (*lttng_ust_clock_freq_function)(void);
+typedef int (*lttng_ust_clock_uuid_function)(char *uuid);
+typedef const char *(*lttng_ust_clock_name_function)(void);
+typedef const char *(*lttng_ust_clock_description_function)(void);
+
 /*
- * Set clock override read callback. This callback should return the
+ * Set/Get clock override read callback. This callback should return the
  * current clock time (a 64-bit monotonic counter).
  */
-int lttng_ust_trace_clock_set_read64_cb(uint64_t (*read64)(void));
+int lttng_ust_trace_clock_set_read64_cb(lttng_ust_clock_read64_function read64_cb);
+int lttng_ust_trace_clock_get_read64_cb(lttng_ust_clock_read64_function *read64_cb);
 
 /*
- * Set clock override frequency callback. This callback should return
+ * Set/Get clock override frequency callback. This callback should return
  * the frequency of the clock in cycles per second.
  */
-int lttng_ust_trace_clock_set_freq_cb(uint64_t (*freq)(void));
+int lttng_ust_trace_clock_set_freq_cb(lttng_ust_clock_freq_function freq_cb);
+int lttng_ust_trace_clock_get_freq_cb(lttng_ust_clock_freq_function *freq_cb);
 
 /*
- * Set clock override unique identifier.
+ * Set/Get clock override unique identifier.
  * LTTNG_UST_UUID_STR_LEN is the maximum length of uuid string. Includes
  * final \0.
  */
 #define LTTNG_UST_UUID_STR_LEN         37
 
-int lttng_ust_trace_clock_set_uuid_cb(int (*uuid)(char *uuid));
+int lttng_ust_trace_clock_set_uuid_cb(lttng_ust_clock_uuid_function uuid_cb);
+int lttng_ust_trace_clock_get_uuid_cb(lttng_ust_clock_uuid_function *uuid_cb);
 
 /*
- * Set clock override name.
+ * Set/Get clock override name.
  */
-int lttng_ust_trace_clock_set_name_cb(const char *(*name)(void));
+int lttng_ust_trace_clock_set_name_cb(lttng_ust_clock_name_function name_cb);
+int lttng_ust_trace_clock_get_name_cb(lttng_ust_clock_name_function *name_cb);
 
 /*
- * Set clock override description.
+ * Set/Get clock override description.
  */
-int lttng_ust_trace_clock_set_description_cb(const char *(*description)(void));
+int lttng_ust_trace_clock_set_description_cb(lttng_ust_clock_description_function description_cb);
+int lttng_ust_trace_clock_get_description_cb(lttng_ust_clock_description_function *description_cb);
 
 /*
  * Use the clock override rather than the default clock.

diff --git a/liblttng-ust/clock.h b/liblttng-ust/clock.h
index b68e563f6206b1eb6394011dfd96522d3587f9c7..824df431f408d881e85d98990e0b98337ed98bff 100644 (file)
--- a/liblttng-ust/clock.h
+++ b/liblttng-ust/clock.h
@@ -19,7 +19,7 @@
 
 #include "lttng-ust-uuid.h"
 
-struct lttng_trace_clock {
+struct lttng_ust_trace_clock {
        uint64_t (*read64)(void);
        uint64_t (*freq)(void);
        int (*uuid)(char *uuid);
@@ -27,7 +27,8 @@ struct lttng_trace_clock {
        const char *(*description)(void);
 };
 
-extern struct lttng_trace_clock *lttng_trace_clock;
+__attribute__((visibility("hidden")))
+extern struct lttng_ust_trace_clock *lttng_ust_trace_clock;
 
 void lttng_ust_clock_init(void);
 
@@ -48,7 +49,7 @@ uint64_t trace_clock_read64_monotonic(void)
 static __inline__
 uint64_t trace_clock_read64(void)
 {
-       struct lttng_trace_clock *ltc = CMM_LOAD_SHARED(lttng_trace_clock);
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
 
        if (caa_likely(!ltc)) {
                return trace_clock_read64_monotonic();

diff --git a/liblttng-ust/lttng-clock.c b/liblttng-ust/lttng-clock.c
index 93a5075d8a2b0db1693246fa44ac09df298c4ee8..27ecccd91cc2da6e1ad97bb1b80ede3a66030a42 100644 (file)
--- a/liblttng-ust/lttng-clock.c
+++ b/liblttng-ust/lttng-clock.c
@@ -9,6 +9,7 @@
 #include <dlfcn.h>
 #include <stdlib.h>
 #include <stdint.h>
+#include <stdio.h>
 #include <usterr-signal-safe.h>
 #include <lttng/ust-clock.h>
 #include <urcu/system.h>
@@ -17,57 +18,167 @@
 #include "clock.h"
 #include "getenv.h"
 
-struct lttng_trace_clock *lttng_trace_clock;
+struct lttng_ust_trace_clock *lttng_ust_trace_clock;
 
 static
-struct lttng_trace_clock user_tc;
+struct lttng_ust_trace_clock user_tc;
 
 static
 void *clock_handle;
 
-int lttng_ust_trace_clock_set_read64_cb(uint64_t (*read64)(void))
+static
+uint64_t trace_clock_freq_monotonic(void)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       return 1000000000ULL;
+}
+
+static
+int trace_clock_uuid_monotonic(char *uuid)
+{
+       int ret = 0;
+       size_t len;
+       FILE *fp;
+
+       /*
+        * boot_id needs to be read once before being used concurrently
+        * to deal with a Linux kernel race. A fix is proposed for
+        * upstream, but the work-around is needed for older kernels.
+        */
+       fp = fopen("/proc/sys/kernel/random/boot_id", "r");
+       if (!fp) {
+               return -ENOENT;
+       }
+       len = fread(uuid, 1, LTTNG_UST_UUID_STR_LEN - 1, fp);
+       if (len < LTTNG_UST_UUID_STR_LEN - 1) {
+               ret = -EINVAL;
+               goto end;
+       }
+       uuid[LTTNG_UST_UUID_STR_LEN - 1] = '\0';
+end:
+       fclose(fp);
+       return ret;
+}
+
+static
+const char *trace_clock_name_monotonic(void)
+{
+       return "monotonic";
+}
+
+static
+const char *trace_clock_description_monotonic(void)
+{
+       return "Monotonic Clock";
+}
+
+int lttng_ust_trace_clock_set_read64_cb(lttng_ust_clock_read64_function read64_cb)
+{
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
-       user_tc.read64 = read64;
+       user_tc.read64 = read64_cb;
+       return 0;
+}
+
+int lttng_ust_trace_clock_get_read64_cb(lttng_ust_clock_read64_function *read64_cb)
+{
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
+
+       if (caa_likely(!ltc)) {
+               *read64_cb = &trace_clock_read64_monotonic;
+       } else {
+               cmm_read_barrier_depends();     /* load ltc before content */
+               *read64_cb = ltc->read64;
+       }
        return 0;
 }
 
-int lttng_ust_trace_clock_set_freq_cb(uint64_t (*freq)(void))
+int lttng_ust_trace_clock_set_freq_cb(lttng_ust_clock_freq_function freq_cb)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
-       user_tc.freq = freq;
+       user_tc.freq = freq_cb;
        return 0;
 }
 
-int lttng_ust_trace_clock_set_uuid_cb(int (*uuid)(char *uuid))
+int lttng_ust_trace_clock_get_freq_cb(lttng_ust_clock_freq_function *freq_cb)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
+
+       if (caa_likely(!ltc)) {
+               *freq_cb = &trace_clock_freq_monotonic;
+       } else {
+               cmm_read_barrier_depends();     /* load ltc before content */
+               *freq_cb = ltc->freq;
+       }
+       return 0;
+}
+
+int lttng_ust_trace_clock_set_uuid_cb(lttng_ust_clock_uuid_function uuid_cb)
+{
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
-       user_tc.uuid = uuid;
+       user_tc.uuid = uuid_cb;
+       return 0;
+}
+
+int lttng_ust_trace_clock_get_uuid_cb(lttng_ust_clock_uuid_function *uuid_cb)
+{
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
+
+       if (caa_likely(!ltc)) {
+               *uuid_cb = &trace_clock_uuid_monotonic;
+       } else {
+               cmm_read_barrier_depends();     /* load ltc before content */
+               *uuid_cb = ltc->uuid;
+       }
        return 0;
 }
 
-int lttng_ust_trace_clock_set_name_cb(const char *(*name)(void))
+int lttng_ust_trace_clock_set_name_cb(lttng_ust_clock_name_function name_cb)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
-       user_tc.name = name;
+       user_tc.name = name_cb;
        return 0;
 }
 
-int lttng_ust_trace_clock_set_description_cb(const char *(*description)(void))
+int lttng_ust_trace_clock_get_name_cb(lttng_ust_clock_name_function *name_cb)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
+
+       if (caa_likely(!ltc)) {
+               *name_cb = &trace_clock_name_monotonic;
+       } else {
+               cmm_read_barrier_depends();     /* load ltc before content */
+               *name_cb = ltc->name;
+       }
+       return 0;
+}
+
+int lttng_ust_trace_clock_set_description_cb(lttng_ust_clock_description_function description_cb)
+{
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
-       user_tc.description = description;
+       user_tc.description = description_cb;
+       return 0;
+}
+
+int lttng_ust_trace_clock_get_description_cb(lttng_ust_clock_description_function *description_cb)
+{
+       struct lttng_ust_trace_clock *ltc = CMM_LOAD_SHARED(lttng_ust_trace_clock);
+
+       if (caa_likely(!ltc)) {
+               *description_cb = &trace_clock_description_monotonic;
+       } else {
+               cmm_read_barrier_depends();     /* load ltc before content */
+               *description_cb = ltc->description;
+       }
        return 0;
 }
 
 int lttng_ust_enable_trace_clock_override(void)
 {
-       if (CMM_LOAD_SHARED(lttng_trace_clock))
+       if (CMM_LOAD_SHARED(lttng_ust_trace_clock))
                return -EBUSY;
        if (!user_tc.read64)
                return -EINVAL;
@@ -79,7 +190,7 @@ int lttng_ust_enable_trace_clock_override(void)
                return -EINVAL;
        /* Use default uuid cb when NULL */
        cmm_smp_mb();   /* Store callbacks before trace clock */
-       CMM_STORE_SHARED(lttng_trace_clock, &user_tc);
+       CMM_STORE_SHARED(lttng_ust_trace_clock, &user_tc);
        return 0;
 }