Add logd.ready

logd.ready is a system property that logd sets when it is ready to
serve incoming socket requests for reading and writing logs. Clients of
logd (e.g. logcat) can use this to synchronize with logd, otherwise they
may experience a crash due to the refused socket connection to logd when
they are started before logd is ready.

Bug: 206826522
Test: run microdroid. see logcat logs are shown immediately
Change-Id: Iee13485b0f4c2beda9bc8434f514c4e32e119492

microdroid/system/private/logcat.te

@@ -12,4 +12,8 @@ allow logcat serial_device:chr_file ra_file_perms;
 # logcat can get logs from logd
 read_logd(logcat)
 
+# Allow logcat to read ro.logd.ready so that it waits until logd is ready to
+# accept commands
+get_prop(logcat, logd_prop)
+
 allow logcat self:global_capability_class_set { sys_nice };

microdroid/system/private/property_contexts

@@ -38,6 +38,7 @@ sys.powerctl            u:object_r:powerctl_prop:s0
 service.adb.root u:object_r:shell_prop:s0 exact bool
 
 ro.logd.kernel u:object_r:logd_prop:s0 exact bool
+logd.ready     u:object_r:logd_prop:s0 exact bool
 
 ro.config.low_ram u:object_r:build_prop:s0 exact bool
 

private/logpersist.te

@@ -15,6 +15,7 @@ userdebug_or_eng(`
 
   control_logd(logpersist)
   unix_socket_connect(logpersist, logdr, logd)
+  get_prop(logpersist, logd_prop)
   read_runtime_log_tags(logpersist)
 
 ')

public/shell.te

@@ -8,6 +8,7 @@ net_domain(shell)
 # logcat
 read_logd(shell)
 control_logd(shell)
+get_prop(shell, logd_prop)
 # logcat -L (directly, or via dumpstate)
 allow shell pstorefs:dir search;
 allow shell pstorefs:file r_file_perms;