pservice: initial version

The can be convenient for running commands or services as procd services
without needing to separately write initscripts, just uci configuration.

The package was imported from [1].

 [1] https://github.com/yousong/waller/tree/0a85f5c75fb70627f68cbbcab4807e02e3299e2e/pservice

Ref: https://github.com/yousong/waller/issues/1
Signed-off-by: Yousong Zhou <yszhou4tech@gmail.com>

utils/pservice/README.md

@@ -0,0 +1,44 @@
+# uci
+
+`disabled`, bool, default `0`
+
+`name`, string, name of the service instance
+
+`command`, file, the service instance executable
+
+`args`, list of args
+
+`stderr`, bool, default `0`, log stderr output of the service instance
+
+`stdout`, bool, default `0`, log stdout output of the service instance
+
+`env`, list of environment variable settings of the form `var=val`
+
+`file`, list of file names.  Service instances will be restarted if content of
+these files have changed on service reload event.
+
+`respawn_threshold`, uinteger, default `3600`, time in seconds the instances
+have to be in running state to be considered a valid run
+
+`respawn_timeout`, uinteger, default `5`, time in seconds the instance should
+be delayed to start again after the last crash
+
+`respawn_maxfail`, uinteger, default `5`, maximum times the instances can
+crash/fail in a row and procd will not try to bring it up again after this
+limit has been reached
+
+# notes and faq
+
+Initial environment variables presented to service instances may be different
+from what was observed on the interactive terminal.  E.g. `HOME=/` may affect
+reading `~/.ssh/known_hosts` of dropbear ssh instance.
+
+	PATH=/usr/sbin:/usr/bin:/sbin:/bin PWD=/ HOME=/
+
+If `list args xxx` seems to be too long causing pain, consider using `/bin/sh`
+as the `command`.  It is also worth noting that uci supports multi-line option
+value.
+
+Child processes will keep running when their parent process was killed.  This
+is especially the case and should be taken into account with option `command`
+being `/bin/sh` and it is recommended to use `exec` as the last shell command.