Do not run tasks if required mounts are not present.

A configuration item `imports.mounts` is added to
`etc/config.yaml`. This should be a list of paths
which must be non-empty. If any of the paths in that
list is empty, runner.sh will abort.

Closes #200.

bin/check_mounts_present.py

@@ -0,0 +1,27 @@
+#!/usr/bin/python3
+
+"""
+Check if any of the directories provided in the imports.mounts configuration
+section are empty.
+
+Returns 0 if all arguments are non-empty, 1 otherwise. It stops at the first
+empty directory.
+"""
+
+import os
+import configuration
+
+cfg = configuration.read()
+
+if cfg and "imports" in cfg and "mounts" in cfg["imports"]:
+
+	mounts = cfg["imports"]["mounts"]
+	for item in mounts:
+		with os.scandir(item) as contents:
+			if not any(contents):
+				exit(1)
+
+else:
+	print("No mounts in configuration")
+
+exit(0)

bin/runner.sh

@@ -107,6 +107,12 @@ echo "$$" > "$LOCKFILE" || {
 }
 print_info "Start run"
 
+print_log "Check if data is accessible"
+$BINDIR/check_mounts_present.py || {
+	print_warning "Import mounts not accessible. Inhibiting all tasks!"
+	exit 253
+}
+
 print_log "Purge deleted files"
 run $BINDIR/purge_deleted_files.py
 

etc/config.yaml

@@ -32,6 +32,13 @@ imports:
     # least this many seconds ago.
     file_min_age: 60
 
+    # These paths refer to remote mounts which must be present in order
+    # for imports to work. If any of these paths are empty, import actions
+    # (including data deletion) will be inhibited. This is to cope with
+    # things like transient network failures.
+    mounts:
+        - /srv/mnt/Data
+
 queues:
     asaqc:
         request: