trace reads on file descriptors

ext/memprof.c

@@ -1835,6 +1835,7 @@ Init_memprof()
   install_malloc_tracer();
   install_gc_tracer();
   install_objcount_tracer();
+  install_fd_tracer();
 
   gc_hook = Data_Wrap_Struct(rb_cObject, sourcefile_marker, NULL, NULL);
   rb_global_variable(&gc_hook);

ext/tracers/fd.c

@@ -0,0 +1,88 @@
+#include <assert.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/time.h>
+
+#include "arch.h"
+#include "bin_api.h"
+#include "tracer.h"
+#include "tramp.h"
+#include "util.h"
+
+struct memprof_fd_stats {
+  size_t read_calls;
+  double read_time;
+  size_t read_requested_bytes;
+  size_t read_actual_bytes;
+
+  size_t readv_calls;
+  size_t write_calls;
+  size_t writev_calls;
+};
+
+static struct tracer tracer;
+static struct memprof_fd_stats memprof_fd_stats;
+
+static ssize_t
+read_tramp(int fildes, void *buf, size_t nbyte) {
+  struct timeval start, end;
+  double secs = 0;
+  int err;
+  ssize_t ret;
+
+  gettimeofday (&start, NULL);
+  ret = read(fildes, buf, nbyte);
+  err = errno;
+  gettimeofday (&end, NULL);
+
+  secs += end.tv_sec - start.tv_sec;
+  secs += (end.tv_usec - start.tv_usec) / 1000000.0;
+
+  memprof_fd_stats.read_time += secs;
+  memprof_fd_stats.read_calls++;
+  memprof_fd_stats.read_requested_bytes += nbyte;
+  if (ret > 0)
+    memprof_fd_stats.read_actual_bytes += ret;
+
+  errno = err;
+  return ret;
+}
+
+static void
+fd_trace_start() {
+  struct tramp_st2_entry tmp;
+  tmp.addr = read_tramp;
+  bin_update_image("read", &tmp, NULL);
+}
+
+static void
+fd_trace_stop() {
+  // TODO: figure out how to undo the tramp
+}
+
+static void
+fd_trace_reset() {
+  memset(&memprof_fd_stats, 0, sizeof(memprof_fd_stats));
+}
+
+static void
+fd_trace_dump() {
+  fprintf(stderr, "================ FDs ======================================\n");
+  fprintf(stderr, " # read calls: %zd\n", memprof_fd_stats.read_calls);
+  fprintf(stderr, " time in read: %fs\n", memprof_fd_stats.read_time);
+  fprintf(stderr, " bytes: %zd requested / %zd actual\n", memprof_fd_stats.read_requested_bytes, memprof_fd_stats.read_actual_bytes);
+  fprintf(stderr, "===========================================================\n\n");
+}
+
+void install_fd_tracer()
+{
+  tracer.start = fd_trace_start;
+  tracer.stop = fd_trace_stop;
+  tracer.reset = fd_trace_reset;
+  tracer.dump = fd_trace_dump;
+  tracer.id = strdup("fd_tracer");
+
+  trace_insert(&tracer);
+}