tb_plugin: follow symlinks when looking for runs (#327)

This commit makes `walk`-ing directories follow symlinks when searching
for run data (on local filesystems, where it's supported!).

This makes the plugin's search behavior consistent with that of
tensorboard itself; using symlink trees to organize runs is one of the
recommendations made in the tensorboard docs to have fine-grained
control over the naming of runs and the location of the data [1]:

> TensorBoard walks log directories recursively; for finer-grained
> control, prefer using a symlink tree.

A unit test is added to validate the new behavior.

[1] https://github.com/tensorflow/tensorboard/blob/master/README.md#logdir--logdir_spec-legacy-mode

tb_plugin/test/test_tensorboard_end2end.py

@@ -1,6 +1,8 @@
 import json
 import os
+import shutil
 import socket
+import tempfile
 import time
 import unittest
 import urllib
@@ -9,6 +11,10 @@
 from urllib.error import HTTPError
 
 
+def get_samples_dir():
+    return os.path.join(os.path.dirname(os.path.abspath(__file__)), '../samples')
+
+
 class TestEnd2End(unittest.TestCase):
 
     #def test_tensorboard_gs(self):
@@ -17,24 +23,41 @@ class TestEnd2End(unittest.TestCase):
     #    self._test_tensorboard_with_arguments(test_folder, expected_runs, {'TORCH_PROFILER_START_METHOD':'spawn'})
 
     def test_tensorboard_end2end(self):
-        test_folder = os.path.join(os.path.dirname(os.path.abspath(__file__)),'../samples')
+        test_folder = get_samples_dir()
         expected_runs = b'["resnet50_num_workers_0", "resnet50_num_workers_4"]'
 
         print("starting spawn mode testing...")
         self._test_tensorboard_with_arguments(test_folder, expected_runs, {'TORCH_PROFILER_START_METHOD':'spawn'})
 
     def test_tensorboard_fork(self):
-        test_folder = os.path.join(os.path.dirname(os.path.abspath(__file__)),'../samples')
+        test_folder = get_samples_dir()
         expected_runs = b'["resnet50_num_workers_0", "resnet50_num_workers_4"]'
 
         print("starting fork mode testing")
         self._test_tensorboard_with_arguments(test_folder, expected_runs)
 
     def test_tensorboard_with_path_prefix(self):
-        test_folder = os.path.join(os.path.dirname(os.path.abspath(__file__)),'../samples')
+        test_folder = get_samples_dir()
         expected_runs = b'["resnet50_num_workers_0", "resnet50_num_workers_4"]'
         self._test_tensorboard_with_arguments(test_folder, expected_runs, path_prefix='/tensorboard/viewer/')
 
+    def test_tensorboard_with_symlinks(self):
+        logdir = tempfile.mkdtemp(prefix="tensorboard_logdir")
+
+        samples_dir = get_samples_dir()
+
+        # Create the following layout, with 1 symlink to a run dir, and 1 regular run dir:
+        # logdir/
+        #     run_concrete/
+        #     run_symlink/ --> path/to/samples/resnet50_num_workers_4/
+        shutil.copytree(os.path.join(samples_dir, "resnet50_num_workers_0"), os.path.join(logdir, "run_concrete"))
+        os.symlink(os.path.join(samples_dir, "resnet50_num_workers_4"), os.path.join(logdir, "run_symlink"))
+
+        expected_runs = b'["run_concrete", "run_symlink"]'
+        self._test_tensorboard_with_arguments(logdir, expected_runs)
+
+        shutil.rmtree(logdir)
+
     def _test_tensorboard_with_arguments(self, test_folder, expected_runs, env=None, path_prefix=None):
         host='localhost'
         port=7007

tb_plugin/torch_tb_profiler/io/file.py

@@ -159,7 +159,11 @@ def stat(self, filename):
         return StatData(file_length)
 
     def walk(self, top, topdown=True, onerror=None):
-        yield from os.walk(top, topdown, onerror)
+        # Note on followlinks=True: per the tensorboard documentation [1], users are encouraged to
+        # use symlink trees to have fine-grained control over the filesystem layout of runs. To
+        # support such trees, we must follow links.
+        # [1] https://github.com/tensorflow/tensorboard/blob/master/README.md#logdir--logdir_spec-legacy-mode
+        yield from os.walk(top, topdown, onerror, followlinks=True)
 
 class S3FileSystem(RemotePath, BaseFileSystem):
     """Provides filesystem access to S3."""