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// -*- mode:C++; tab-width:8; c-basic-offset:2; indent-tabs-mode:t -*-
// vim: ts=8 sw=2 smarttab
#ifndef CEPH_COMMON_PREFORKER_H
#define CEPH_COMMON_PREFORKER_H
#include <signal.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <unistd.h>
#include <sstream>
#include "common/errno.h"
#include "common/safe_io.h"
#include "include/ceph_assert.h"
#include "include/compat.h"
#include "include/sock_compat.h"
/**
* pre-fork fork/daemonize helper class
*
* Hide the details of letting a process fork early, do a bunch of
* initialization work that may spam stdout or exit with an error, and
* then daemonize. The exit() method will either exit directly (if we
* haven't forked) or pass a message to the parent with the error if
* we have.
*/
class Preforker {
pid_t childpid;
bool forked;
int fd[2]; // parent's, child's
public:
Preforker()
: childpid(0),
forked(false)
{}
int prefork(std::string &err) {
ceph_assert(!forked);
std::ostringstream oss;
int r = socketpair_cloexec(AF_UNIX, SOCK_STREAM, 0, fd);
if (r < 0) {
int e = errno;
oss << "[" << getpid() << "]: unable to create socketpair: " << cpp_strerror(e);
err = oss.str();
return (errno = e, -1);
}
struct sigaction sa;
sa.sa_handler = SIG_IGN;
sigemptyset(&sa.sa_mask);
sa.sa_flags = 0;
if (sigaction(SIGHUP, &sa, nullptr) != 0) {
int e = errno;
oss << "[" << getpid() << "]: unable to ignore SIGHUP: " << cpp_strerror(e);
err = oss.str();
return (errno = e, -1);
}
forked = true;
childpid = fork();
if (childpid < 0) {
int e = errno;
oss << "[" << getpid() << "]: unable to fork: " << cpp_strerror(e);
err = oss.str();
return (errno = e, -1);
}
if (is_child()) {
::close(fd[0]);
} else {
::close(fd[1]);
}
return 0;
}
int get_signal_fd() const {
return forked ? fd[1] : 0;
}
bool is_child() {
return childpid == 0;
}
bool is_parent() {
return childpid != 0;
}
int parent_wait(std::string &err_msg) {
ceph_assert(forked);
int r = -1;
std::ostringstream oss;
int err = safe_read_exact(fd[0], &r, sizeof(r));
if (err == 0 && r == -1) {
// daemonize
::close(0);
::close(1);
::close(2);
r = 0;
} else if (err) {
oss << "[" << getpid() << "]: " << cpp_strerror(err);
} else {
// wait for child to exit
int status;
err = waitpid(childpid, &status, 0);
if (err < 0) {
oss << "[" << getpid() << "]" << " waitpid error: " << cpp_strerror(err);
} else if (WIFSIGNALED(status)) {
oss << "[" << getpid() << "]" << " exited with a signal";
} else if (!WIFEXITED(status)) {
oss << "[" << getpid() << "]" << " did not exit normally";
} else {
err = WEXITSTATUS(status);
if (err != 0)
oss << "[" << getpid() << "]" << " returned exit_status " << cpp_strerror(err);
}
}
err_msg = oss.str();
return err;
}
int signal_exit(int r) {
if (forked) {
/* If we get an error here, it's too late to do anything reasonable about it. */
[[maybe_unused]] auto n = safe_write(fd[1], &r, sizeof(r));
}
return r;
}
void exit(int r) {
if (is_child())
signal_exit(r);
::exit(r);
}
void daemonize() {
ceph_assert(forked);
static int r = -1;
int r2 = ::write(fd[1], &r, sizeof(r));
r += r2; // make the compiler shut up about the unused return code from ::write(2).
}
};
#endif
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