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-rw-r--r--nix/libutil/util.cc84
-rw-r--r--nix/libutil/util.hh25
2 files changed, 109 insertions, 0 deletions
diff --git a/nix/libutil/util.cc b/nix/libutil/util.cc
index 17d145b4c6..59a2981359 100644
--- a/nix/libutil/util.cc
+++ b/nix/libutil/util.cc
@@ -1142,5 +1142,89 @@ void ignoreException()
}
}
+static const string pathNullDevice = "/dev/null";
+
+/* Common initialisation performed in child processes. */
+void commonChildInit(Pipe & logPipe)
+{
+ /* Put the child in a separate session (and thus a separate
+ process group) so that it has no controlling terminal (meaning
+ that e.g. ssh cannot open /dev/tty) and it doesn't receive
+ terminal signals. */
+ if (setsid() == -1)
+ throw SysError(format("creating a new session"));
+
+ /* Dup the write side of the logger pipe into stderr. */
+ if (dup2(logPipe.writeSide, STDERR_FILENO) == -1)
+ throw SysError("cannot pipe standard error into log file");
+
+ /* Dup stderr to stdout. */
+ if (dup2(STDERR_FILENO, STDOUT_FILENO) == -1)
+ throw SysError("cannot dup stderr into stdout");
+
+ /* Reroute stdin to /dev/null. */
+ int fdDevNull = open(pathNullDevice.c_str(), O_RDWR);
+ if (fdDevNull == -1)
+ throw SysError(format("cannot open `%1%'") % pathNullDevice);
+ if (dup2(fdDevNull, STDIN_FILENO) == -1)
+ throw SysError("cannot dup null device into stdin");
+ close(fdDevNull);
+}
+
+//////////////////////////////////////////////////////////////////////
+
+Agent::Agent(const string &command, const Strings &args)
+{
+ debug(format("starting agent '%1%'") % command);
+
+ /* Create a pipe to get the output of the child. */
+ fromAgent.create();
+
+ /* Create the communication pipes. */
+ toAgent.create();
+
+ /* Create a pipe to get the output of the builder. */
+ builderOut.create();
+
+ /* Fork the hook. */
+ pid = startProcess([&]() {
+
+ commonChildInit(fromAgent);
+
+ if (chdir("/") == -1) throw SysError("changing into `/");
+
+ /* Dup the communication pipes. */
+ if (dup2(toAgent.readSide, STDIN_FILENO) == -1)
+ throw SysError("dupping to-hook read side");
+
+ /* Use fd 4 for the builder's stdout/stderr. */
+ if (dup2(builderOut.writeSide, 4) == -1)
+ throw SysError("dupping builder's stdout/stderr");
+
+ Strings allArgs;
+ allArgs.push_back(command);
+ allArgs.insert(allArgs.end(), args.begin(), args.end()); // append
+
+ execv(command.c_str(), stringsToCharPtrs(allArgs).data());
+
+ throw SysError(format("executing `%1%'") % command);
+ });
+
+ pid.setSeparatePG(true);
+ fromAgent.writeSide.close();
+ toAgent.readSide.close();
+}
+
+
+Agent::~Agent()
+{
+ try {
+ toAgent.writeSide.close();
+ pid.kill(true);
+ } catch (...) {
+ ignoreException();
+ }
+}
+
}
diff --git a/nix/libutil/util.hh b/nix/libutil/util.hh
index 9e3c14bdd4..13cff44316 100644
--- a/nix/libutil/util.hh
+++ b/nix/libutil/util.hh
@@ -264,6 +264,29 @@ public:
void setKillSignal(int signal);
};
+/* An "agent" is a helper program that runs in the background and that we talk
+ to over pipes, such as the "guix offload" program. */
+struct Agent
+{
+ /* Pipes for talking to the agent. */
+ Pipe toAgent;
+
+ /* Pipe for the agent's standard output/error. */
+ Pipe fromAgent;
+
+ /* Pipe for build standard output/error--e.g., for build processes started
+ by "guix offload". */
+ Pipe builderOut;
+
+ /* The process ID of the agent. */
+ Pid pid;
+
+ /* The command and arguments passed to the agent. */
+ Agent(const string &command, const Strings &args);
+
+ ~Agent();
+};
+
/* Kill all processes running under the specified uid by sending them
a SIGKILL. */
@@ -295,6 +318,8 @@ void closeMostFDs(const set<int> & exceptions);
/* Set the close-on-exec flag for the given file descriptor. */
void closeOnExec(int fd);
+/* Common initialisation performed in child processes. */
+void commonChildInit(Pipe & logPipe);
/* User interruption. */