Implement --shm-path option for UST sessions (per-uid channels)

[lttng-tools.git] / src / bin / lttng-sessiond / ust-metadata.c

diff --git a/src/bin/lttng-sessiond/ust-metadata.c b/src/bin/lttng-sessiond/ust-metadata.c
index b0f83d2721654b0351c872f082997bef2b0dc881..f4f273b16cc7021e2f4869e52b42dfd7f14799dd 100644 (file)
--- a/src/bin/lttng-sessiond/ust-metadata.c
+++ b/src/bin/lttng-sessiond/ust-metadata.c
@@ -20,6 +20,7 @@
  */
 
 #define _GNU_SOURCE
+#define _LGPL_SOURCE
 #include <stdint.h>
 #include <string.h>
 #include <stdarg.h>
@@ -37,6 +38,13 @@
 #define max_t(type, a, b)      ((type) ((a) > (b) ? (a) : (b)))
 #endif
 
+#define NR_CLOCK_OFFSET_SAMPLES                10
+
+struct offset_sample {
+       uint64_t offset;                /* correlation offset */
+       uint64_t measure_delta;         /* lower is better */
+};
+
 static inline
 int fls(unsigned int x)
 {
@@ -112,6 +120,23 @@ ssize_t metadata_reserve(struct ust_registry_session *session, size_t len)
        return ret;
 }
 
+static
+int metadata_file_append(struct ust_registry_session *session,
+               const char *str, size_t len)
+{
+       ssize_t written;
+
+       if (session->metadata_fd < 0) {
+               return 0;
+       }
+       /* Write to metadata file */
+       written = lttng_write(session->metadata_fd, str, len);
+       if (written != len) {
+               return -1;
+       }
+       return 0;
+}
+
 /*
  * We have exclusive access to our metadata buffer (protected by the
  * ust_lock), so we can do racy operations such as looking for
@@ -141,6 +166,11 @@ int lttng_metadata_printf(struct ust_registry_session *session,
                goto end;
        }
        memcpy(&session->metadata[offset], str, len);
+       ret = metadata_file_append(session, str, len);
+       if (ret) {
+               PERROR("Error appending to metadata file");
+               goto end;
+       }
        DBG3("Append to metadata: \"%s\"", str);
        ret = 0;
 
@@ -490,31 +520,57 @@ int _lttng_event_header_declare(struct ust_registry_session *session)
        );
 }
 
-/*
- * Approximation of NTP time of day to clock monotonic correlation,
- * taken at start of trace.
- * Yes, this is only an approximation. Yes, we can (and will) do better
- * in future versions.
- */
 static
-uint64_t measure_clock_offset(void)
+int measure_single_clock_offset(struct offset_sample *sample)
 {
-       uint64_t offset, monotonic[2], realtime;
+       uint64_t offset, monotonic[2], measure_delta, realtime;
        struct timespec rts = { 0, 0 };
        int ret;
 
        monotonic[0] = trace_clock_read64();
        ret = clock_gettime(CLOCK_REALTIME, &rts);
-       if (ret < 0)
-               return 0;
+       if (ret < 0) {
+               return ret;
+       }
        monotonic[1] = trace_clock_read64();
+       measure_delta = monotonic[1] - monotonic[0];
+       if (measure_delta > sample->measure_delta) {
+               /*
+                * Discard value if it took longer to read than the best
+                * sample so far.
+                */
+               return 0;
+       }
        offset = (monotonic[0] + monotonic[1]) >> 1;
        realtime = (uint64_t) rts.tv_sec * 1000000000ULL;
        realtime += rts.tv_nsec;
        offset = realtime - offset;
-       return offset;
+       sample->offset = offset;
+       sample->measure_delta = measure_delta;
+       return 0;
 }
 
+/*
+ * Approximation of NTP time of day to clock monotonic correlation,
+ * taken at start of trace. Keep the measurement that took the less time
+ * to complete, thus removing imprecision caused by preemption.
+ */
+static
+uint64_t measure_clock_offset(void)
+{
+       int i;
+       struct offset_sample offset_best_sample = {
+               .offset = 0,
+               .measure_delta = UINT64_MAX,
+       };
+
+       for (i = 0; i < NR_CLOCK_OFFSET_SAMPLES; i++) {
+               if (measure_single_clock_offset(&offset_best_sample)) {
+                       return 0;
+               }
+       }
+       return offset_best_sample.offset;
+}
 
 /*
  * Should be called with session registry mutex held.
@@ -541,6 +597,15 @@ int ust_metadata_session_statedump(struct ust_registry_session *session,
                uuid_c[8], uuid_c[9], uuid_c[10], uuid_c[11],
                uuid_c[12], uuid_c[13], uuid_c[14], uuid_c[15]);
 
+       /* For crash ABI */
+       ret = lttng_metadata_printf(session,
+               "/* CTF %u.%u */\n\n",
+               CTF_SPEC_MAJOR,
+               CTF_SPEC_MINOR);
+       if (ret) {
+               goto end;
+       }
+
        ret = lttng_metadata_printf(session,
                "typealias integer { size = 8; align = %u; signed = false; } := uint8_t;\n"
                "typealias integer { size = 16; align = %u; signed = false; } := uint16_t;\n"