r/repohost: Optimize createrepo queue loop

Instead of waking every 30 seconds, the queue loop in
`repohost-createrepo.sh` now only wakes when it receives an inotify
event indicating the queue file has been modified.  To avoid missing
events that occured while a `createrepo` process was running, there's
now an inner loop that runs until the queue is completely empty, before
returning to blocking on `inotifywait`.

roles/repohost/files/repohost-createrepo.sh

@@ -1,19 +1,31 @@
 #!/bin/sh
+# vim: set sw=4 ts=4 sts=4 et :
 
 QFILE="${HOME}"/createrepo.queue
 REPOS_ROOT="${HOME}"/repos
 
+wait_queue() {
+    inotifywait \
+        --event close_write \
+        --include "${QFILE##*/}" \
+        "${QFILE%/*}"
+}
+
 createrepo_loop() {
-    while sleep 30; do
-        [ -f "${QFILE}" ] || continue
-        mv "${QFILE}" "${QFILE}.work"
+    while wait_queue; do
+        while [ -f "${QFILE}" ]; do
+            sleep 10
+            flock "${QFILE}" mv "${QFILE}" "${QFILE}.work"
             sort -u "${QFILE}.work" > "${QFILE}.sorted"
             while read dir; do
+                if [ -d "${dir}" ]; then
                     printf 'Generating repository metadata for %s\n' "${dir}"
                     createrepo_c "${dir}"
+                fi
             done < "${QFILE}.sorted"
             rm -f "${QFILE}.work" "${QFILE}.sorted"
         done
+    done
 }
 
 inotify_loop() {