init.rc: logd: Add logpersistd (nee logcatd)

- logpersistd is defined as a thread or process in the context of the
  logd domain. Here we define logpersistd as logcat -f in logd domain
  and call it logcatd to represent its service mechanics.
- Use logcatd to manage content in /data/misc/logd/ directory.
- Only turn on for persist.logd.logpersistd = logcatd.
- Add logpersist.start, logpersist.stop and logpersist.cat debug
  class executables, thus only in the eng and userdebug builds.

ToDo: Wish to add Developer Options menu to turn this feature on or
off, complicated by the fact that user builds have no tools with
access rights to /data/misc/logd.

Bug: 19608716
Change-Id: I57ad757f121c473d04f9fabe9d4820a0eca06f31
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 0966038..1f421c5 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -649,3 +649,17 @@
     class late_start
     user root
     oneshot
+
+on property:persist.logd.logpersistd=logcatd
+    # all exec/services are called with umask(077), so no gain beyond 0700
+    mkdir /data/misc/logd 0700 logd log
+    # logd for write to /data/misc/logd, log group for read from pstore (-L)
+    exec - logd log -- /system/bin/logcat -L -b all -v threadtime -v usec -v printable -D -f /data/misc/logd/logcat -r 64 -n 256
+    start logcatd
+
+service logcatd /system/bin/logcat -b all -v threadtime -v usec -v printable -D -f /data/misc/logd/logcat -r 64 -n 256
+    class late_start
+    disabled
+    # logd for write to /data/misc/logd, log group for read from log daemon
+    user logd
+    group log