MEDIUM: add haproxy-systemd-wrapper

Currently, to reload haproxy configuration, you have to use "-sf".

There is a problem with this way of doing things. First of all, in the systemd world,
reload commands should be "oneshot" ones, which means they should not be the new main
process but rather a tool which makes a call to it and then exits. With the current approach,
the reload command is the new main command and moreover, it makes the previous one exit.
Systemd only tracks the main program, seeing it ending, it assumes it either finished or failed,
and kills everything remaining as a grabage collector. We then end up with no haproxy running
at all.

This patch adds wrapper around haproxy, no changes at all have been made into it,
so it's not intrusive and doesn't change anything for other hosts. What this wrapper does
is basically launching haproxy as a child, listen to the SIGUSR2 (not to conflict with
haproxy itself) signal, and spawing a new haproxy with "-sf" as a child to relay the
first one.

Signed-off-by: Marc-Antoine Perennou <Marc-Antoine@Perennou.com>

.gitignore

@@ -12,6 +12,7 @@ src/*.o
 *.log*
 *.trace*
 haproxy-*
+!src/*.c
 make-*
 dlmalloc.c
 00*.patch

Makefile

@@ -593,7 +593,7 @@ all:
 	@echo
 	@exit 1
 else
-all: haproxy
+all: haproxy haproxy-systemd-wrapper
 endif
 
 OBJS = src/haproxy.o src/sessionhash.o src/base64.o src/protocol.o \
@@ -618,12 +618,17 @@ ifneq ($(TRACE),)
 OBJS += src/trace.o
 endif
 
+WRAPPER_OBJS = src/haproxy-systemd-wrapper.o
+
 # Not used right now
 LIB_EBTREE = $(EBTREE_DIR)/libebtree.a
 
 haproxy: $(OBJS) $(OPTIONS_OBJS) $(EBTREE_OBJS)
 	$(LD) $(LDFLAGS) -o $@ $^ $(LDOPTS)
 
+haproxy-systemd-wrapper: $(WRAPPER_OBJS)
+	$(LD) $(LDFLAGS) -o $@ $^ $(LDOPTS)
+
 $(LIB_EBTREE): $(EBTREE_OBJS)
 	$(AR) rv $@ $^
 
@@ -646,6 +651,11 @@ src/haproxy.o:	src/haproxy.c
 	      -DBUILD_OPTIONS='"$(strip $(BUILD_OPTIONS))"' \
 	       -c -o $@ $<
 
+src/haproxy-systemd-wrapper.o:	src/haproxy-systemd-wrapper.c
+	$(CC) $(COPTS) \
+	      -DSBINDIR='"$(strip $(SBINDIR))"' \
+	       -c -o $@ $<
+
 src/dlmalloc.o: $(DLMALLOC_SRC)
 	$(CC) $(COPTS) -DDEFAULT_MMAP_THRESHOLD=$(DLMALLOC_THRES) -c -o $@ $<
 
@@ -659,9 +669,10 @@ install-doc:
 		install -m 644 doc/$$x.txt $(DESTDIR)$(DOCDIR) ; \
 	done
 
-install-bin: haproxy
+install-bin: haproxy haproxy-systemd-wrapper
 	install -d $(DESTDIR)$(SBINDIR)
 	install haproxy $(DESTDIR)$(SBINDIR)
+	install haproxy-systemd-wrapper $(DESTDIR)$(SBINDIR)
 
 install: install-bin install-man install-doc
 
@@ -670,6 +681,7 @@ clean:
 	for dir in . src include/* doc ebtree; do rm -f $$dir/*~ $$dir/*.rej $$dir/core; done
 	rm -f haproxy-$(VERSION).tar.gz haproxy-$(VERSION)$(SUBVERS).tar.gz
 	rm -f haproxy-$(VERSION) nohup.out gmon.out
+	rm -f haproxy-systemd-wrapper
 
 tags:
 	find src include \( -name '*.c' -o -name '*.h' \) -print0 | \

src/haproxy-systemd-wrapper.c

@@ -0,0 +1,114 @@
+/*
+ * Wrapper to make haproxy systemd-compliant.
+ *
+ * Copyright 2013 Marc-Antoine Perennou <Marc-Antoine@Perennou.com>
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version
+ * 2 of the License, or (at your option) any later version.
+ *
+ */
+
+#include <errno.h>
+#include <signal.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <unistd.h>
+#include <sys/wait.h>
+
+static pid_t pid = 0;
+static char *pid_file = "/run/haproxy.pid";
+static int main_argc;
+static char **main_argv;
+
+static pid_t spawn_haproxy(char **pid_strv, int nb_pid)
+{
+	pid_t pid = fork();
+	if (!pid) {
+		/* 3 for "haproxy -Ds -sf" */
+		char **argv = calloc(4 + main_argc + nb_pid + 1, sizeof(char *));
+		int i;
+		int argno = 0;
+		argv[argno++] = SBINDIR"/haproxy";
+		for (i = 0; i < main_argc; ++i)
+			argv[argno++] = main_argv[i];
+		argv[argno++] = "-Ds";
+		if (nb_pid > 0) {
+			argv[argno++] = "-sf";
+			for (i = 0; i < nb_pid; ++i)
+				argv[argno++] = pid_strv[i];
+		}
+		argv[argno] = NULL;
+		execv(argv[0], argv);
+		exit(0);
+	}
+	return pid;
+}
+
+static int read_pids(char ***pid_strv)
+{
+	FILE *f = fopen(pid_file, "r");
+	int read = 0, allocated = 8;
+	char pid_str[10];
+
+	if (!f)
+		return 0;
+
+	*pid_strv = malloc(allocated * sizeof(char *));
+	while (1 == fscanf(f, "%s\n", pid_str)) {
+		if (read == allocated) {
+			allocated *= 2;
+			*pid_strv = realloc(*pid_strv, allocated * sizeof(char *));
+		}
+		(*pid_strv)[read++] = strdup(pid_str);
+	}
+
+	fclose(f);
+
+	return read;
+}
+
+static void signal_handler(int signum __attribute__((unused)))
+{
+	int i;
+	char **pid_strv = NULL;
+	int nb_pid = read_pids(&pid_strv);
+
+	pid = spawn_haproxy(pid_strv, nb_pid);
+
+	for (i = 0; i < nb_pid; ++i)
+		free(pid_strv[i]);
+	free(pid_strv);
+}
+
+static void init(int argc, char **argv)
+{
+	while (argc > 1) {
+		if (**argv == '-') {
+			char *flag = *argv + 1;
+			--argc; ++argv;
+			if (*flag == 'p')
+				pid_file = *argv;
+		}
+		--argc; ++argv;
+	}
+}
+
+int main(int argc, char **argv)
+{
+	--argc; ++argv;
+        main_argc = argc;
+        main_argv = argv;
+
+	init(argc, argv);
+
+	signal(SIGUSR2, &signal_handler);
+
+	pid = spawn_haproxy(NULL, 0);
+	while (-1 != waitpid(pid, NULL, 0) || errno == EINTR);
+
+	return EXIT_SUCCESS;
+}