PR docs buildbot: check free space/inodes, only build PR docs on request

 * docs build for PRs can be requested by putting "+DOCS" somewhere in the
   github comments
 * current docs buildbot server has relatively low inode quota, avoid again
   using up all inodes

see obspy#1357

misc/scripts/docs_buildbot/update-docs-pr.sh

@@ -1,6 +1,28 @@
 #!/bin/bash
+
 cd $HOME
 anaconda3/bin/python update_pull_request_metadata.py
+
+# check free space and free inodes (current docs server has relatively low
+# inode quota)
+## `df` on docs server doesn't have "output" option
+## FREE_INODES = `df . --output="iavail" | tail -1`
+FREE_INODES = `df $HOME/htdocs -i | tail -1 | awk '{print $4}'`
+INODE_CRITICAL = "300000"  # 300k
+if [ "$FREE_INODES" -lt "$INODE_CRITICAL" ]
+then
+    echo "Aborting PR docs build, low inodes: $FREE_INODES"
+    exit 1
+fi
+FREE_SPACE = `df $HOME/htdocs/ | tail -1 | awk '{print $4}'`
+SPACE_CRITICAL = "10000000"  # 10G
+if [ "$FREE_SPACE" -lt "$SPACE_CRITICAL" ]
+then
+    echo "Aborting PR docs build, low disk space: $FREE_INODES"
+    exit 1
+fi
+
+
 for FILE in `ls pull_request_docs/*.todo 2> /dev/null`
 do
     PR=${FILE##*/}

misc/scripts/docs_buildbot/update_pull_request_metadata.py

@@ -1,8 +1,23 @@
 import os
+import re
 import requests
 from obspy import UTCDateTime
 
 
+def check_docs_build_requested(issue_number):
+    """
+    Check if a docs build was requested for given issue number (by magic string
+    '+DOCS' anywhere in issue comments).
+
+    :rtype: bool
+    """
+    url = "https://api.github.com/repos/obspy/obspy/issues/{:d}/comments"
+    data = requests.get(url.format(issue_number), params={"per_page": 100})
+    comments = [x["body"] for x in data.json()]
+    pattern = r'\+DOCS'
+    return any(re.search(pattern, comment) for comment in comments)
+
+
 try:
     # github API token with "repo.status" access right
     token = os.environ["OBSPY_COMMIT_STATUS_TOKEN"]
@@ -27,6 +42,8 @@
 for d in data:
     # extract the pieces we need from the PR data
     number = d['number']
+    if not check_docs_build_requested(number):
+        continue
     fork = d['head']['user']['login']
     branch = d['head']['ref']
     commit = d['head']['sha']