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#include "spawner.hh"
#include "image_processor.hh"
#include "io.hh"
#include "unique_fd.hh"
#include <cassert>
#include <csignal>
#include <expected>
#include <linux/prctl.h>
#include <memory>
#include <sys/prctl.h>
#include <sys/syscall.h>
#include <unistd.h>
#include <utility>
namespace {
int pidfd_getfd(int pidfd, int targetfd, unsigned int flags) {
return static_cast<int>(syscall(SYS_pidfd_getfd, pidfd, targetfd, flags));
}
// NOLINTNEXTLINE(misc-include-cleaner)
int pidfd_open(pid_t pid, unsigned int flags) {
return static_cast<int>(syscall(SYS_pidfd_open, pid, flags));
}
class ProcessImpl : public Process {
public:
ProcessImpl(
pid_t pid,
std::pair<std::unique_ptr<io::Reader>, std::unique_ptr<io::Writer>> pipe)
: pid_(pid), pipe_(std::move(pipe)) {
assert(pid_);
}
[[nodiscard]]
pid_t pid() const { return pid_; }
[[nodiscard]]
io::Reader& reader() const override { return *pipe_.first; }
[[nodiscard]]
io::Writer& writer() const override { return *pipe_.second; }
void kill() {
if (pid_ != 0) {
::kill(pid_, SIGTERM); // NOLINT(misc-include-cleaner)
pid_ = 0;
}
}
private:
pid_t pid_;
std::pair<std::unique_ptr<io::Reader>, std::unique_ptr<io::Writer>> pipe_;
};
struct Request {
Spawner::Exec exec;
int reader;
int writer;
};
struct Response {
pid_t pid;
};
void spawner_runner(unique_fd parent, std::unique_ptr<io::Reader> reader,
std::unique_ptr<io::Writer> writer) {
while (true) {
Request request;
{
auto ret = reader->repeat_read(&request, sizeof(request));
if (!ret.has_value() || ret.value() != sizeof(request)) {
break;
}
}
// Need to not return a response before child has duped fds.
// So use a short-lived pipe to sync child start.
auto sync_pipe = io::pipe();
pid_t child_pid = 0;
if (sync_pipe.has_value()) {
child_pid = fork();
if (child_pid == 0) {
// Child process
sync_pipe->first.reset();
reader.reset();
writer.reset();
unique_fd child_reader_fd{pidfd_getfd(parent.get(), request.reader, 0)};
unique_fd child_writer_fd{pidfd_getfd(parent.get(), request.writer, 0)};
parent.reset();
if (child_reader_fd && child_writer_fd) {
char c = 1;
if (sync_pipe->second->write(&c, sizeof(c)).has_value()) {
auto child_reader = io::reader_from_raw(child_reader_fd.release());
auto child_writer = io::writer_from_raw(child_writer_fd.release());
switch (request.exec) {
case Spawner::Exec::kImageProcessor:
_exit(image_processor::run(std::move(child_reader),
std::move(child_writer)));
}
}
}
_exit(1);
// _exit obviously never returns but to help tools and compilers…
return;
}
// Parent process
if (child_pid == -1) {
// fork() failed, we use zero as error value.
child_pid = 0;
} else {
sync_pipe->second.reset();
char c = 1;
std::ignore = sync_pipe->first->read(&c, sizeof(c));
}
}
Response response{child_pid};
{
auto ret = writer->repeat_write(&response, sizeof(response));
if (!ret.has_value() || ret.value() != sizeof(response)) {
break;
}
}
}
}
class SpawnerImpl : public Spawner {
public:
explicit SpawnerImpl(std::unique_ptr<ProcessImpl> process)
: process_(std::move(process)) {}
~SpawnerImpl() override {
if (process_) {
process_->kill();
}
}
[[nodiscard]]
std::expected<std::unique_ptr<Process>, Error> run(Exec exec) override {
if (!process_) {
return std::unexpected(Error::kError);
}
auto reader_pipe = io::pipe();
auto writer_pipe = io::pipe();
if (!reader_pipe.has_value() || !writer_pipe.has_value()) {
return std::unexpected(Error::kError);
}
Request req{
.exec = exec,
.reader = writer_pipe->first->raw_fd(),
.writer = reader_pipe->second->raw_fd(),
};
{
auto ret = process_->writer().repeat_write(&req, sizeof(req));
if (!ret.has_value() || ret.value() != sizeof(req)) {
process_->kill();
process_.reset();
return std::unexpected(Error::kError);
}
}
Response resp;
{
auto ret = process_->reader().repeat_read(&resp, sizeof(resp));
if (!ret.has_value() || ret.value() != sizeof(resp)) {
process_->kill();
process_.reset();
return std::unexpected(Error::kError);
}
}
if (resp.pid == 0)
return std::unexpected(Error::kError);
return std::make_unique<ProcessImpl>(
resp.pid, std::make_pair(std::move(reader_pipe->first),
std::move(writer_pipe->second)));
}
private:
std::unique_ptr<ProcessImpl> process_;
};
} // namespace
std::expected<std::unique_ptr<Spawner>, Spawner::Error> Spawner::create() {
auto reader_pipe = io::pipe();
auto writer_pipe = io::pipe();
if (!reader_pipe.has_value() || !writer_pipe.has_value()) {
return std::unexpected(Error::kError);
}
auto pid = getpid();
unique_fd pidfd{pidfd_open(pid, 0)};
if (!pidfd) {
return std::unexpected(Error::kError);
}
// Needed for pidfd_getfd to work in child.
if (prctl(PR_SET_PTRACER, pid) != 0) {
return std::unexpected(Error::kError);
}
pid = fork();
if (pid == 0) {
// Child process
reader_pipe->first.reset();
writer_pipe->second.reset();
spawner_runner(std::move(pidfd), std::move(writer_pipe->first),
std::move(reader_pipe->second));
_exit(0);
}
// Parent process
if (pid == -1) {
return std::unexpected(Error::kError);
}
return std::make_unique<SpawnerImpl>(std::make_unique<ProcessImpl>(
pid, std::make_pair(std::move(reader_pipe->first),
std::move(writer_pipe->second))));
}
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