init: add stdio_to_kmsg option

Some services are not native android services and therefore don't log
via the normal mechanisms.  This gives developers an option to have
their stdout/stderr logs sent directly to kmsg.

Test: see test prints to kernel log
Change-Id: I7973ea74d5cab3a90c2cd9a3d5de2266439d0c01

init/README.md

@@ -170,6 +170,8 @@ runs the service.
   be changed by setting the "androidboot.console" kernel parameter. In
   all cases the leading "/dev/" should be omitted, so "/dev/tty0" would be
   specified as just "console tty0".
+  This option connects stdin, stdout, and stderr to the console. It is mutually exclusive with the
+  stdio_to_kmsg option, which only connects stdout and stderr to kmsg.
 
 `critical`
 > This is a device-critical service. If it exits more than four times in
@@ -313,6 +315,13 @@ runs the service.
   seclabel or computed based on the service executable file security context.
   For native executables see libcutils android\_get\_control\_socket().
 
+`stdio_to_kmsg`
+> Redirect stdout and stderr to /dev/kmsg_debug. This is useful for services that do not use native
+  Android logging during early boot and whose logs messages we want to capture. This is only enabled
+  when /dev/kmsg_debug is enabled, which is only enabled on userdebug and eng builds.
+  This is mutually exclusive with the console option, which additionally connects stdin to the
+  given console.
+
 `timeout_period <seconds>`
 > Provide a timeout after which point the service will be killed. The oneshot keyword is respected
   here, so oneshot services do not automatically restart, however all other services will.

init/service_parser.cpp

@@ -83,6 +83,9 @@ Result<void> ServiceParser::ParseClass(std::vector<std::string>&& args) {
 }
 
 Result<void> ServiceParser::ParseConsole(std::vector<std::string>&& args) {
+    if (service_->proc_attr_.stdio_to_kmsg) {
+        return Error() << "'console' and 'stdio_to_kmsg' are mutually exclusive";
+    }
     service_->flags_ |= SVC_CONSOLE;
     service_->proc_attr_.console = args.size() > 1 ? "/dev/" + args[1] : "";
     return {};
@@ -429,6 +432,14 @@ Result<void> ServiceParser::ParseSocket(std::vector<std::string>&& args) {
     return {};
 }
 
+Result<void> ServiceParser::ParseStdioToKmsg(std::vector<std::string>&& args) {
+    if (service_->flags_ & SVC_CONSOLE) {
+        return Error() << "'stdio_to_kmsg' and 'console' are mutually exclusive";
+    }
+    service_->proc_attr_.stdio_to_kmsg = true;
+    return {};
+}
+
 // name type
 Result<void> ServiceParser::ParseFile(std::vector<std::string>&& args) {
     if (args[2] != "r" && args[2] != "w" && args[2] != "rw") {
@@ -514,6 +525,7 @@ const KeywordMap<ServiceParser::OptionParser>& ServiceParser::GetParserMap() con
         {"shutdown",                {1,     1,    &ServiceParser::ParseShutdown}},
         {"sigstop",                 {0,     0,    &ServiceParser::ParseSigstop}},
         {"socket",                  {3,     6,    &ServiceParser::ParseSocket}},
+        {"stdio_to_kmsg",           {0,     0,    &ServiceParser::ParseStdioToKmsg}},
         {"timeout_period",          {1,     1,    &ServiceParser::ParseTimeoutPeriod}},
         {"updatable",               {0,     0,    &ServiceParser::ParseUpdatable}},
         {"user",                    {1,     1,    &ServiceParser::ParseUser}},

init/service_parser.h

@@ -75,6 +75,7 @@ class ServiceParser : public SectionParser {
     Result<void> ParseShutdown(std::vector<std::string>&& args);
     Result<void> ParseSigstop(std::vector<std::string>&& args);
     Result<void> ParseSocket(std::vector<std::string>&& args);
+    Result<void> ParseStdioToKmsg(std::vector<std::string>&& args);
     Result<void> ParseTimeoutPeriod(std::vector<std::string>&& args);
     Result<void> ParseFile(std::vector<std::string>&& args);
     Result<void> ParseUser(std::vector<std::string>&& args);

init/service_utils.cpp

@@ -16,10 +16,12 @@
 
 #include "service_utils.h"
 
+#include <fcntl.h>
 #include <grp.h>
 #include <sys/mount.h>
 #include <sys/prctl.h>
 #include <sys/wait.h>
+#include <unistd.h>
 
 #include <android-base/file.h>
 #include <android-base/logging.h>
@@ -121,11 +123,15 @@ Result<void> SetUpPidNamespace(const char* name) {
     return {};
 }
 
-void ZapStdio() {
+void SetupStdio(bool stdio_to_kmsg) {
     auto fd = unique_fd{open("/dev/null", O_RDWR | O_CLOEXEC)};
-    dup2(fd, 0);
-    dup2(fd, 1);
-    dup2(fd, 2);
+    dup2(fd, STDIN_FILENO);
+    if (stdio_to_kmsg) {
+        fd.reset(open("/dev/kmsg_debug", O_WRONLY | O_CLOEXEC));
+        if (fd == -1) fd.reset(open("/dev/null", O_WRONLY | O_CLOEXEC));
+    }
+    dup2(fd, STDOUT_FILENO);
+    dup2(fd, STDERR_FILENO);
 }
 
 void OpenConsole(const std::string& console) {
@@ -238,7 +244,7 @@ Result<void> SetProcessAttributes(const ProcessAttributes& attr) {
         if (setpgid(0, getpid()) == -1) {
             return ErrnoError() << "setpgid failed";
         }
-        ZapStdio();
+        SetupStdio(attr.stdio_to_kmsg);
     }
 
     for (const auto& rlimit : attr.rlimits) {

init/service_utils.h

@@ -77,6 +77,7 @@ struct ProcessAttributes {
     gid_t gid;
     std::vector<gid_t> supp_gids;
     int priority;
+    bool stdio_to_kmsg;
 };
 Result<void> SetProcessAttributes(const ProcessAttributes& attr);