unix: use oldest ctime,atime,mtime as birthtime

When the operating system does not support birthtime for stat,
previously behaviour was to use the ctime (last changed) time instead.

This change instead enforces that uv_fs_stat will use the oldest
available time (of ctime, atime, and mtime) rather than arbitrarily
picking ctime.

Fixes: nodejs/node#2222

src/unix/fs.c

@@ -701,8 +701,24 @@ static void uv__to_stat(struct stat* src, uv_stat_t* dst) {
   dst->st_mtim.tv_nsec = src->st_mtime_nsec;
   dst->st_ctim.tv_sec = src->st_ctime;
   dst->st_ctim.tv_nsec = src->st_ctime_nsec;
-  dst->st_birthtim.tv_sec = src->st_ctime;
-  dst->st_birthtim.tv_nsec = src->st_ctime_nsec;
+
+  /* On systems that do not support birthtime, resolve the value to the least
+   * time available (oldest of atime, mtime, ctime), disregarding nanoseconds.
+   */
+  if (src->st_atime < src->st_mtime && src->st_atime < src->st_ctime) {
+    /* Use last accessed time. */
+    dst->st_birthtim.tv_sec = src->st_atime;
+    dst->st_birthtim.tv_nsec = src->st_atime_nsec;
+  } else if (src->st_mtime < src->st_ctime) {
+    /* Use last modified time. */
+    dst->st_birthtim.tv_sec = src->st_mtime;
+    dst->st_birthtim.tv_nsec = src->st_mtime_nsec;
+  } else {
+    /* Use last change time. */
+    dst->st_birthtim.tv_sec = src->st_ctime;
+    dst->st_birthtim.tv_nsec = src->st_ctime_nsec;
+  }
+
   dst->st_flags = 0;
   dst->st_gen = 0;
 #elif !defined(_AIX) && (       \
@@ -725,8 +741,23 @@ static void uv__to_stat(struct stat* src, uv_stat_t* dst) {
   dst->st_flags = src->st_flags;
   dst->st_gen = src->st_gen;
 # else
-  dst->st_birthtim.tv_sec = src->st_ctim.tv_sec;
-  dst->st_birthtim.tv_nsec = src->st_ctim.tv_nsec;
+  /* On systems that do not support birthtime, resolve the value to the least
+   * time available (oldest of atime, mtime, ctime), disregarding nanoseconds.
+   */
+  if (src->st_atime < src->st_mtime && src->st_atime < src->st_ctime) {
+    /* Use last accessed time. */
+    dst->st_birthtim.tv_sec = src->st_atim.tv_sec;
+    dst->st_birthtim.tv_nsec = src->st_atim.tv_nsec;
+  } else if (src->st_mtime < src->st_ctime) {
+    /* Use last modified time. */
+    dst->st_birthtim.tv_sec = src->st_mtim.tv_sec;
+    dst->st_birthtim.tv_nsec = src->st_mtim.tv_nsec;
+  } else {
+    /* Use last change time. */
+    dst->st_birthtim.tv_sec = src->st_ctim.tv_sec;
+    dst->st_birthtim.tv_nsec = src->st_ctim.tv_nsec;
+  }
+
   dst->st_flags = 0;
   dst->st_gen = 0;
 # endif

test/test-fs.c

@@ -2535,3 +2535,63 @@ TEST_IMPL(fs_read_write_null_arguments) {
 
   return 0;
 }
+
+
+TEST_IMPL(fs_stat_small_birthtime) {
+  int r;
+  long birthtime;
+  uv_buf_t* iovs;
+
+  unlink("test_file");
+
+  loop = uv_default_loop();
+
+  /* First open the file, then write and read, in that order. uv_fs_stat used
+   * to give preference to ctime, which would in this case give the smaller
+   * time. In this case, atime will be the returned birthtime, for systems that
+   * do not support birthtime.
+   */
+  r = uv_fs_open(loop,
+                 &open_req1,
+                 "test_file",
+                 O_RDWR | O_CREAT,
+                 S_IWUSR | S_IRUSR,
+                 NULL);
+  ASSERT(r >= 0);
+  uv_fs_req_cleanup(&open_req1);
+
+  iovs = malloc(sizeof(*iovs) * 1);
+  iovs[0] = uv_buf_init(test_buf, sizeof(test_buf));
+
+  r = uv_fs_write(loop, &write_req, open_req1.result, iovs, 1, 0, NULL);
+  ASSERT(r >= 0);
+  uv_fs_req_cleanup(&write_req);
+
+  r = uv_fs_read(loop, &read_req, open_req1.result, iovs, 1, 0, NULL);
+  ASSERT(r >= 0);
+  uv_fs_req_cleanup(&read_req);
+
+  /* And now, we test. */
+
+  r = uv_fs_stat(loop, &stat_req, "test_file", NULL);
+  ASSERT(r >= 0);
+  ASSERT(stat_req.result >= 0);
+
+  /* Birthtime must be less than or equal to all of the other stat time fields:
+   * ctime, atime, and mtime.
+   */
+  birthtime = stat_req.statbuf.st_birthtim.tv_sec;
+
+  ASSERT(birthtime <= stat_req.statbuf.st_ctim.tv_sec);
+  ASSERT(birthtime <= stat_req.statbuf.st_atim.tv_sec);
+  ASSERT(birthtime <= stat_req.statbuf.st_mtim.tv_sec);
+
+  /* Cleanup. */
+  uv_fs_req_cleanup(&stat_req);
+  unlink("test_file");
+  free(iovs);
+
+  MAKE_VALGRIND_HAPPY();
+
+  return 0;
+}

test/test-list.h

@@ -276,6 +276,7 @@ TEST_DECLARE   (fs_open_dir)
 TEST_DECLARE   (fs_rename_to_existing_file)
 TEST_DECLARE   (fs_write_multiple_bufs)
 TEST_DECLARE   (fs_read_write_null_arguments)
+TEST_DECLARE   (fs_stat_small_birthtime)
 TEST_DECLARE   (fs_write_alotof_bufs)
 TEST_DECLARE   (fs_write_alotof_bufs_with_offset)
 TEST_DECLARE   (threadpool_queue_work_simple)
@@ -692,6 +693,7 @@ TASK_LIST_START
   TEST_ENTRY  (fs_write_alotof_bufs)
   TEST_ENTRY  (fs_write_alotof_bufs_with_offset)
   TEST_ENTRY  (fs_read_write_null_arguments)
+  TEST_ENTRY  (fs_stat_small_birthtime)
   TEST_ENTRY  (threadpool_queue_work_simple)
   TEST_ENTRY  (threadpool_queue_work_einval)
   TEST_ENTRY  (threadpool_multiple_event_loops)