add kubernetes pause

Add the k8s pause binary to `pause/pause.c` and do the plumbing in the
Makefile to install it in $libexec/podman/pause/pause.  It is intended to
replace the k8s pause image and hence the need for network connectivity
when creating pods.

[NO NEW TESTS NEEDED] since it will be tested in a following commit.

Signed-off-by: Valentin Rothberg <rothberg@redhat.com>

Makefile

@@ -185,6 +185,10 @@ ifdef HOMEBREW_PREFIX
 endif
 endif
 
+# For building pause/pause.c
+GCC ?= gcc
+PAUSE_CFLAGS = -Os -static -Wall -Werror -DVERSION=v$(RELEASE_VERSION)
+
 ###
 ### Primary entry-point targets
 ###
@@ -196,7 +200,7 @@ default: all
 all: binaries docs
 
 .PHONY: binaries
-binaries: podman podman-remote rootlessport ## Build podman, podman-remote and rootlessport binaries
+binaries: podman podman-remote rootlessport pause
 
 # Extract text following double-# for targets, as their description for
 # the `help` target.  Otherwise These simple-substitutions are resolved
@@ -374,6 +378,12 @@ bin/rootlessport: .gopathok $(SOURCES) go.mod go.sum
 .PHONY: rootlessport
 rootlessport: bin/rootlessport
 
+bin/pause: pause/pause.c
+	$(GCC) $(PAUSE_CFLAGS) pause/pause.c -o bin/pause
+
+.PHONY: pause
+pause: bin/pause
+
 ###
 ### Secondary binary-build targets
 ###
@@ -733,7 +743,7 @@ install.remote-nobuild:
 install.remote: podman-remote install.remote-nobuild
 
 .PHONY: install.bin-nobuild
-install.bin-nobuild:
+install.bin-nobuild: install.pause
 	install ${SELINUXOPT} -d -m 755 $(DESTDIR)$(BINDIR)
 	install ${SELINUXOPT} -m 755 bin/podman $(DESTDIR)$(BINDIR)/podman
 	test -z "${SELINUXOPT}" || chcon --verbose --reference=$(DESTDIR)$(BINDIR)/podman bin/podman
@@ -787,8 +797,10 @@ install.docker-docs-nobuild:
 .PHONY: install.docker-docs
 install.docker-docs: docker-docs install.docker-docs-nobuild
 
-.PHONY: install.docker-full
+.PHONY: install.pause
-install.docker-full: install.docker install.docker-docs
+install.pause: pause
+	install ${SELINUXOPT} -m 755 -d $(DESTDIR)$(LIBEXECPODMAN)/pause
+	install ${SELINUXOPT} -m 755 bin/pause $(DESTDIR)$(LIBEXECPODMAN)/pause/pause
 
 .PHONY: install.systemd
 ifneq (,$(findstring systemd,$(BUILDTAGS)))
@@ -819,6 +831,9 @@ else
 install.systemd:
 endif
 
+.PHONY: install.pause
+install.pause: pause
+
 .PHONY: install.tools
 install.tools: .install.goimports .install.gitvalidation .install.md2man .install.ginkgo .install.golangci-lint .install.bats ## Install needed tools
 

contrib/spec/podman.spec.in

@@ -528,6 +528,7 @@ export GOPATH=%{buildroot}/%{gopath}:$(pwd)/vendor:%{gopath}
 %{_usr}/lib/tmpfiles.d/podman.conf
 %dir %{_libexecdir}/%{name}
 %{_libexecdir}/%{name}/rootlessport
+%{_libexecdir}/%{name}/pause/pause
 
 %if 0%{?with_devel}
 %files -n libpod-devel -f devel.file-list

pause/pause.c

@@ -0,0 +1,69 @@
+/*
+Copyright 2016 The Kubernetes Authors.
+Copyright 2021 The Podman Authors.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+#include <signal.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <unistd.h>
+
+#define STRINGIFY(x) #x
+#define VERSION_STRING(x) STRINGIFY(x)
+
+#ifndef VERSION
+#define VERSION HEAD
+#endif
+
+static void sigdown(int signo) {
+  psignal(signo, "Shutting down, got signal");
+  exit(0);
+}
+
+static void sigreap(int signo) {
+  while (waitpid(-1, NULL, WNOHANG) > 0)
+    ;
+}
+
+int main(int argc, char **argv) {
+  int i;
+  for (i = 1; i < argc; ++i) {
+    if (!strcasecmp(argv[i], "-v")) {
+      printf("pause.c %s\n", VERSION_STRING(VERSION));
+      return 0;
+    }
+  }
+
+  if (getpid() != 1)
+    /* Not an error because pause sees use outside of infra containers. */
+    fprintf(stderr, "Warning: pause should be the first process\n");
+
+  if (sigaction(SIGINT, &(struct sigaction){.sa_handler = sigdown}, NULL) < 0)
+    return 1;
+  if (sigaction(SIGTERM, &(struct sigaction){.sa_handler = sigdown}, NULL) < 0)
+    return 2;
+  if (sigaction(SIGCHLD, &(struct sigaction){.sa_handler = sigreap,
+                                             .sa_flags = SA_NOCLDSTOP},
+                NULL) < 0)
+    return 3;
+
+  for (;;)
+    pause();
+  fprintf(stderr, "Error: infinite loop terminated\n");
+  return 42;
+}