From cd3bec398808df31042f12daebeff32a8584c519 Mon Sep 17 00:00:00 2001
From: Davin McCall <davmac@davmac.org>
Date: Sat, 17 Nov 2018 00:35:13 +0000
Subject: [PATCH] Add "ready-notification" service option.

This allows either of the two notification methods - write to a specific
fd or to an fd identified by an environment variable.
---
 doc/manpages/dinit-service.5 | 15 +++++++++++++++
 src/load-service.cc          | 34 ++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+)

diff --git a/doc/manpages/dinit-service.5 b/doc/manpages/dinit-service.5
index c594194..34428eb 100644
--- a/doc/manpages/dinit-service.5
+++ b/doc/manpages/dinit-service.5
@@ -220,6 +220,21 @@ to terminate (applies to 'process' services only). SIGTERM is always
 sent along with the specified signal, unless the \fBnosigterm\fR option is
 specified via the \fBoptions\fR parameter.
 .TP
+\fBready-notification\fR = {\fBpipefd:\fR\fIfd-number\fR | \fBpipevar:\fR\fIenv-var-name\fR}
+Specifies the mechanism, if any, by which a process service will notify that it is ready
+(successfully started). If not specified, a process service is considered started as soon as it
+has begun execution. The two options are:
+.RS
+.IP \(bu
+\fBpipefd:\fR\fIfd-number\fR \(em the service will write a message to the specified file descriptor,
+which \fBdinit\fR sets up as the write end of a pipe before execution. This mechanism is compatible
+with the S6 supervision suite.
+.IP \(bu
+\fBpipevar:\fR\fIenv-var-name\fR \(em the service will write a message to file descriptor identified
+using the contents of the specified environment variable, which will be set by \fBdinit\fR before
+execution to a file descriptor (chosen arbitrarily) attached to the write end of a pipe.
+.RE
+.TP
 \fBlogfile\fR = \fIlog-file-path\fR
 Specifies the log file for the service. Output from the service process
 will go this file.
diff --git a/src/load-service.cc b/src/load-service.cc
index 0d66738..318e7b4 100644
--- a/src/load-service.cc
+++ b/src/load-service.cc
@@ -283,6 +283,17 @@ static void process_dep_dir(dirload_service_set &sset,
     }
 }
 
+// Check if one string starts with another
+static bool starts_with(string s, const char *prefix)
+{
+    const char * sp = s.c_str();
+    while (*sp != 0 && *prefix != 0) {
+        if (*sp != *prefix) return false;
+        sp++; prefix++;
+    }
+    return *prefix == 0;
+}
+
 // Find a service record, or load it from file. If the service has
 // dependencies, load those also.
 //
@@ -361,6 +372,9 @@ service_record * dirload_service_set::load_service(const char * name)
     timespec stop_timeout = { .tv_sec = 10, .tv_nsec = 0 };
     timespec start_timeout = { .tv_sec = 60, .tv_nsec = 0 };
     
+    int readiness_fd = -1;      // readiness fd in service process
+    std::string readiness_var;  // environment var to hold readiness fd
+
     uid_t run_as_uid = -1;
     gid_t run_as_gid = -1;
 
@@ -567,6 +581,24 @@ service_record * dirload_service_set::load_service(const char * name)
             else if (setting == "chain-to") {
                 chain_to_name = read_setting_value(i, end, nullptr);
             }
+            else if (setting == "ready-notification") {
+                string notify_setting = read_setting_value(i, end, nullptr);
+                if (starts_with(notify_setting, "pipefd:")) {
+                    readiness_fd = parse_unum_param(notify_setting.substr(7 /* len 'pipefd:' */),
+                            name, std::numeric_limits<int>::max());
+                }
+                else if (starts_with(notify_setting, "pipevar:")) {
+                    readiness_var = notify_setting.substr(8 /* len 'pipevar:' */);
+                    if (readiness_var.empty()) {
+                        throw service_description_exc(name, "Invalid pipevar variable name "
+                                "in ready-notification");
+                    }
+                }
+                else {
+                    throw service_description_exc(name, "Unknown ready-notification setting: "
+                            + notify_setting);
+                }
+            }
             else {
                 throw service_description_exc(name, "Unknown setting: " + setting);
             }
@@ -598,6 +630,8 @@ service_record * dirload_service_set::load_service(const char * name)
                     rvalps->set_extra_termination_signal(term_signal);
                     rvalps->set_run_as_uid_gid(run_as_uid, run_as_gid);
                     rvalps->set_workding_dir(working_dir);
+                    rvalps->set_notification_fd(readiness_fd);
+                    rvalps->set_notification_var(std::move(readiness_var));
                     // process service start / run on console must be the same:
                     onstart_flags.starts_on_console = onstart_flags.runs_on_console;
                     rval = rvalps;
-- 
2.25.1