[libfuzzer] Update documentation on UBSan options and Upload Corpus section.

testing/libfuzzer/clusterfuzz.md

 # libFuzzer and ClusterFuzz Integration
 
 *** note
 Most links on this page are private.
 ***
 
 ClusterFuzz is a distributed fuzzing infrastructure 
 ([go/clusterfuzz](https://goto.google.com/clusterfuzz)) that automatically
 executes libFuzzer tests on scale.
 
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 * ClusterFuzz downloads new binaries once a day and runs fuzzers continuously.
 * Fuzzer run logs are uploaded to [ClusterFuzz libFuzzer Logs] GCS bucket.
 * Fuzzing corpus is maintained for each fuzzer in [Corpus GCS Bucket]. Once a day
 corpus is minimized to reduce number of duplicates and/or reduce effect of 
 parasitic coverage. 
 * [ClusterFuzz Fuzzer Status] displays fuzzer runtime 
 metrics as well as provides links to crashes and coverage reports. The information
 is collected every 30 minutes.
 
 
+## Upload Corpus
+ClusterFuzz uses two corpus types with libFuzzer:
+
+1) **Seed** (or **static**) corpus: files manually uploaded by developers.
+ClusterFuzz uses these files for fuzzing but doesn't delete/overwrite them.
+
+2) **General** (or **working**) corpus: files generated by fuzzers themselves.
+These corpus files are frequently modified during fuzzing sessions and can be
+deleted during corpus minimization.
+
+A fuzzer has two input corpus directories, seed and general, but its output
+goes into general corpus directory. Seed corpus is read-only.
+
+ClusterFuzz supports two sources of seed corpus.
+
+#### Chromium repository

[aizatsky, 2016/04/19 18:42:43]

Let's move this section to efficient_fuzzing.

[mmoroz, 2016/04/20 12:38:20]

Done.

+
+To use corpus stored in the repository you need to add `seed_corpus` attribute
+to fuzzer target:
+
+```
+fuzzer_test("my_protocol_fuzzer") {
+  ...
+  seed_corpus = "src/fuzz/testcases"
+  ...
+}
+```
+
+#### Google Cloud Storage
+
+If you don't want to store seed corpus in Chromium repository, you can upload
+it into Google Cloud Storage bucket:
+
+
+1) go to [Corpus GCS Bucket]
+
+2) open directory named `%YOUR_FUZZER_NAME%_static`
+
+3) upload corpus files into the directory
+
+
+Alternative way is to use `gsutil` tool:
+```bash
+gsutil -m rsync <corpus_dir_on_disk> gs://clusterfuzz-corpus/libfuzzer/%YOUR_FUZZER_NAME%_static
+```
+
 [Buildbot]: https://goto.google.com/libfuzzer-clusterfuzz-buildbot
 [fuzzer_test.gni]: https://code.google.com/p/chromium/codesearch#chromium/src/testing/libfuzzer/fuzzer_test.gni
 [chromium_libfuzzer.py]: https://code.google.com/p/chromium/codesearch#chromium/build/scripts/slave/recipes/chromium_libfuzzer.py
 [ClusterFuzz Fuzzer Status]: https://goto.google.com/libfuzzer-clusterfuzz-status
 [ClusterFuzz libFuzzer Logs]: https://goto.google.com/libfuzzer-clusterfuzz-logs
 [Corpus GCS Bucket]: https://goto.google.com/libfuzzer-clusterfuzz-corpus