libcutils: add support for app tracing

This change adds support for tracing using the ATRACE_TAG_APP tag.  This tag is
enabled only for processes in which the /proc/<pid>/cmdline value appears in
the comma-separated list of such values in the debug.atrace.app_cmdlines system
property.  It is also only enabled if either the ro.debuggable system property
is set to 1 or the application has declared itself debuggable in its manifest,
which gets reported to libcutils by the framework.

Change-Id: Ic94ba55f4e70a9cf994056acbf151e523428b65d

1 files changed, 85 insertions, 5 deletions

diff --git a/libcutils/trace.c b/libcutils/trace.c
index 152ea61..047f889 100644
--- a/libcutils/trace.c
+++ b/libcutils/trace.c
@@ -18,6 +18,7 @@
 #include <fcntl.h>
 #include <limits.h>
 #include <pthread.h>
+#include <stdbool.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/types.h>
@@ -29,11 +30,81 @@
 #define LOG_TAG "cutils-trace"
 #include <cutils/log.h>
 
-int32_t               atrace_is_ready     = 0;
-int                   atrace_marker_fd    = -1;
-uint64_t              atrace_enabled_tags = ATRACE_TAG_NOT_READY;
-static pthread_once_t atrace_once_control = PTHREAD_ONCE_INIT;
-static pthread_mutex_t atrace_tags_mutex = PTHREAD_MUTEX_INITIALIZER;
+int32_t                atrace_is_ready      = 0;
+int                    atrace_marker_fd     = -1;
+uint64_t               atrace_enabled_tags  = ATRACE_TAG_NOT_READY;
+static bool            atrace_is_debuggable = false;
+static pthread_once_t  atrace_once_control  = PTHREAD_ONCE_INIT;
+static pthread_mutex_t atrace_tags_mutex    = PTHREAD_MUTEX_INITIALIZER;
+
+// Set whether this process is debuggable, which determines whether
+// application-level tracing is allowed when the ro.debuggable system property
+// is not set to '1'.
+void atrace_set_debuggable(bool debuggable)
+{
+    atrace_is_debuggable = debuggable;
+    atrace_update_tags();
+}
+
+// Check whether the given command line matches one of the comma-separated
+// values listed in the app_cmdlines property.
+static bool atrace_is_cmdline_match(const char* cmdline) {
+    char value[PROPERTY_VALUE_MAX];
+    char* start = value;
+
+    property_get("debug.atrace.app_cmdlines", value, "");
+
+    while (start != NULL) {
+        char* end = strchr(start, ',');
+
+        if (end != NULL) {
+            *end = '\0';
+            end++;
+        }
+
+        if (strcmp(cmdline, start) == 0) {
+            return true;
+        }
+
+        start = end;
+    }
+
+    return false;
+}
+
+// Determine whether application-level tracing is enabled for this process.
+static bool atrace_is_app_tracing_enabled()
+{
+    bool sys_debuggable = false;
+    bool proc_debuggable = false;
+    char value[PROPERTY_VALUE_MAX];
+    bool result = false;
+
+    // Check whether the system is debuggable.
+    property_get("ro.debuggable", value, "0");
+    if (value[0] == '1') {
+        sys_debuggable = true;
+    }
+
+    if (sys_debuggable || atrace_is_debuggable) {
+        // Check whether tracing is enabled for this process.
+        FILE * file = fopen("/proc/self/cmdline", "r");
+        if (file) {
+            char cmdline[4096];
+            if (fgets(cmdline, sizeof(cmdline), file)) {
+                result = atrace_is_cmdline_match(cmdline);
+            } else {
+                ALOGE("Error reading cmdline: %s (%d)", strerror(errno), errno);
+            }
+            fclose(file);
+        } else {
+            ALOGE("Error opening /proc/self/cmdline: %s (%d)", strerror(errno),
+                    errno);
+        }
+    }
+
+    return result;
+}
 
 // Read the sysprop and return the value tags should be set to
 static uint64_t atrace_get_property()
@@ -52,6 +123,15 @@ static uint64_t atrace_get_property()
         ALOGE("Error parsing trace property: Number too large: %s", value);
         return 0;
     }
+
+    // Only set the "app" tag if this process was selected for app-level debug
+    // tracing.
+    if (atrace_is_app_tracing_enabled()) {
+        tags |= ATRACE_TAG_APP;
+    } else {
+        tags &= ~ATRACE_TAG_APP;
+    }
+
     return (tags | ATRACE_TAG_ALWAYS) & ATRACE_TAG_VALID_MASK;
 }