transmission/libtransmission/subprocess-posix.cc

176 lines
3.9 KiB
C++

// This file Copyright © Mnemosyne LLC.
// It may be used under GPLv2 (SPDX: GPL-2.0-only), GPLv3 (SPDX: GPL-3.0-only),
// or any future license endorsed by Mnemosyne LLC.
// License text can be found in the licenses/ folder.
#include <array>
#include <cerrno>
#include <csignal>
#include <cstdlib>
#include <map>
#include <string>
#include <string_view>
#include <fcntl.h>
#include <sys/wait.h>
#include <unistd.h>
#include <fmt/core.h>
#include "libtransmission/error.h"
#include "libtransmission/subprocess.h"
#include "libtransmission/tr-assert.h"
#include "libtransmission/tr-strbuf.h"
#include "libtransmission/utils.h"
using namespace std::literals;
namespace
{
void handle_sigchld(int /*i*/)
{
int rc = 0;
do
{
/* FIXME: Only check for our own PIDs */
rc = waitpid(-1, nullptr, WNOHANG);
} while (rc > 0 || (rc == -1 && errno == EINTR));
/* FIXME: Call old handler, if any */
}
void set_system_error(tr_error* error, int code, std::string_view what)
{
if (error != nullptr)
{
error->set(code, fmt::format("{:s} failed: {:s} ({:d})", what, tr_strerror(code), code));
}
}
[[nodiscard]] bool tr_spawn_async_in_child(
char const* const* cmd,
std::map<std::string_view, std::string_view> const& env,
std::string_view work_dir)
{
auto key_sz = std::string{};
auto val_sz = std::string{};
for (auto const& [key_sv, val_sv] : env)
{
key_sz = key_sv;
val_sz = val_sv;
if (setenv(key_sz.c_str(), val_sz.c_str(), 1) != 0)
{
return false;
}
}
if (!std::empty(work_dir) && chdir(tr_pathbuf{ work_dir }) == -1)
{
return false;
}
if (execvp(cmd[0], const_cast<char* const*>(cmd)) == -1)
{
return false;
}
return true;
}
[[nodiscard]] bool tr_spawn_async_in_parent(int pipe_fd, tr_error* error)
{
int child_errno = 0;
ssize_t count = 0;
static_assert(sizeof(child_errno) == sizeof(errno));
do
{
count = read(pipe_fd, &child_errno, sizeof(child_errno));
} while (count == -1 && errno == EINTR);
close(pipe_fd);
if (count == -1)
{
/* Read failed (what to do?) */
}
else if (count == 0)
{
/* Child successfully exec-ed */
}
else
{
TR_ASSERT((size_t)count == sizeof(child_errno));
set_system_error(error, child_errno, "Child process setup");
return false;
}
return true;
}
} // namespace
bool tr_spawn_async(
char const* const* cmd,
std::map<std::string_view, std::string_view> const& env,
std::string_view work_dir,
tr_error* error)
{
static bool sigchld_handler_set = false;
if (!sigchld_handler_set)
{
/* FIXME: "The effects of signal() in a multithreaded process are unspecified." © man 2 signal */
if (signal(SIGCHLD, &handle_sigchld) == SIG_ERR) // NOLINT(performance-no-int-to-ptr)
{
set_system_error(error, errno, "Call to signal()");
return false;
}
sigchld_handler_set = true;
}
auto pipe_fds = std::array<int, 2>{};
if (pipe(std::data(pipe_fds)) == -1)
{
set_system_error(error, errno, "Call to pipe()");
return false;
}
if (fcntl(pipe_fds[1], F_SETFD, fcntl(pipe_fds[1], F_GETFD) | FD_CLOEXEC) == -1)
{
set_system_error(error, errno, "Call to fcntl()");
close(pipe_fds[0]);
close(pipe_fds[1]);
return false;
}
int const child_pid = fork();
if (child_pid == -1)
{
set_system_error(error, errno, "Call to fork()");
return false;
}
if (child_pid == 0)
{
close(pipe_fds[0]);
if (!tr_spawn_async_in_child(cmd, env, work_dir))
{
(void)write(pipe_fds[1], &errno, sizeof(errno));
_exit(0);
}
}
close(pipe_fds[1]);
return tr_spawn_async_in_parent(pipe_fds[0], error);
}