1//===-- PseudoTerminal.cpp --------------------------------------*- C++ -*-===//
2//
3// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
4// See https://llvm.org/LICENSE.txt for license information.
5// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
6//
7//===----------------------------------------------------------------------===//
8//
9// Created by Greg Clayton on 1/8/08.
10//
11//===----------------------------------------------------------------------===//
12
13#include "PseudoTerminal.h"
14#include <cstdlib>
15#include <sys/ioctl.h>
16#include <unistd.h>
17
18// PseudoTerminal constructor
19PseudoTerminal::PseudoTerminal()
20 : m_primary_fd(invalid_fd), m_secondary_fd(invalid_fd) {}
21
22// Destructor
23// The primary and secondary file descriptors will get closed if they are
24// valid. Call the ReleasePrimaryFD()/ReleaseSecondaryFD() member functions
25// to release any file descriptors that are needed beyond the lifespan
26// of this object.
27PseudoTerminal::~PseudoTerminal() {
28 ClosePrimary();
29 CloseSecondary();
30}
31
32// Close the primary file descriptor if it is valid.
33void PseudoTerminal::ClosePrimary() {
34 if (m_primary_fd > 0) {
35 ::close(fd: m_primary_fd);
36 m_primary_fd = invalid_fd;
37 }
38}
39
40// Close the secondary file descriptor if it is valid.
41void PseudoTerminal::CloseSecondary() {
42 if (m_secondary_fd > 0) {
43 ::close(fd: m_secondary_fd);
44 m_secondary_fd = invalid_fd;
45 }
46}
47
48// Open the first available pseudo terminal with OFLAG as the
49// permissions. The file descriptor is store in the m_primary_fd member
50// variable and can be accessed via the PrimaryFD() or ReleasePrimaryFD()
51// accessors.
52//
53// Suggested value for oflag is O_RDWR|O_NOCTTY
54//
55// RETURNS:
56// Zero when successful, non-zero indicating an error occurred.
57PseudoTerminal::Status PseudoTerminal::OpenFirstAvailablePrimary(int oflag) {
58 // Open the primary side of a pseudo terminal
59 m_primary_fd = ::posix_openpt(oflag: oflag);
60 if (m_primary_fd < 0) {
61 return err_posix_openpt_failed;
62 }
63
64 // Grant access to the secondary pseudo terminal
65 if (::grantpt(fd: m_primary_fd) < 0) {
66 ClosePrimary();
67 return err_grantpt_failed;
68 }
69
70 // Clear the lock flag on the secondary pseudo terminal
71 if (::unlockpt(fd: m_primary_fd) < 0) {
72 ClosePrimary();
73 return err_unlockpt_failed;
74 }
75
76 return success;
77}
78
79// Open the secondary pseudo terminal for the current primary pseudo
80// terminal. A primary pseudo terminal should already be valid prior to
81// calling this function (see PseudoTerminal::OpenFirstAvailablePrimary()).
82// The file descriptor is stored in the m_secondary_fd member variable and
83// can be accessed via the SecondaryFD() or ReleaseSecondaryFD() accessors.
84//
85// RETURNS:
86// Zero when successful, non-zero indicating an error occurred.
87PseudoTerminal::Status PseudoTerminal::OpenSecondary(int oflag) {
88 CloseSecondary();
89
90 // Open the primary side of a pseudo terminal
91 const char *secondary_name = SecondaryName();
92
93 if (secondary_name == NULL)
94 return err_ptsname_failed;
95
96 m_secondary_fd = ::open(file: secondary_name, oflag: oflag);
97
98 if (m_secondary_fd < 0)
99 return err_open_secondary_failed;
100
101 return success;
102}
103
104// Get the name of the secondary pseudo terminal. A primary pseudo terminal
105// should already be valid prior to calling this function (see
106// PseudoTerminal::OpenFirstAvailablePrimary()).
107//
108// RETURNS:
109// NULL if no valid primary pseudo terminal or if ptsname() fails.
110// The name of the secondary pseudo terminal as a NULL terminated C string
111// that comes from static memory, so a copy of the string should be
112// made as subsequent calls can change this value.
113const char *PseudoTerminal::SecondaryName() const {
114 if (m_primary_fd < 0)
115 return NULL;
116 return ::ptsname(fd: m_primary_fd);
117}
118
119// Fork a child process that and have its stdio routed to a pseudo
120// terminal.
121//
122// In the parent process when a valid pid is returned, the primary file
123// descriptor can be used as a read/write access to stdio of the
124// child process.
125//
126// In the child process the stdin/stdout/stderr will already be routed
127// to the secondary pseudo terminal and the primary file descriptor will be
128// closed as it is no longer needed by the child process.
129//
130// This class will close the file descriptors for the primary/secondary
131// when the destructor is called, so be sure to call ReleasePrimaryFD()
132// or ReleaseSecondaryFD() if any file descriptors are going to be used
133// past the lifespan of this object.
134//
135// RETURNS:
136// in the parent process: the pid of the child, or -1 if fork fails
137// in the child process: zero
138
139pid_t PseudoTerminal::Fork(PseudoTerminal::Status &error) {
140 pid_t pid = invalid_pid;
141 error = OpenFirstAvailablePrimary(O_RDWR | O_NOCTTY);
142
143 if (error == 0) {
144 // Successfully opened our primary pseudo terminal
145
146 pid = ::fork();
147 if (pid < 0) {
148 // Fork failed
149 error = err_fork_failed;
150 } else if (pid == 0) {
151 // Child Process
152 ::setsid();
153
154 error = OpenSecondary(O_RDWR);
155 if (error == 0) {
156 // Successfully opened secondary
157 // We are done with the primary in the child process so lets close it
158 ClosePrimary();
159
160#if defined(TIOCSCTTY)
161 // Acquire the controlling terminal
162 if (::ioctl(fd: m_secondary_fd, TIOCSCTTY, (char *)0) < 0)
163 error = err_failed_to_acquire_controlling_terminal;
164#endif
165 // Duplicate all stdio file descriptors to the secondary pseudo terminal
166 if (::dup2(fd: m_secondary_fd, STDIN_FILENO) != STDIN_FILENO)
167 error = error ? error : err_dup2_failed_on_stdin;
168 if (::dup2(fd: m_secondary_fd, STDOUT_FILENO) != STDOUT_FILENO)
169 error = error ? error : err_dup2_failed_on_stdout;
170 if (::dup2(fd: m_secondary_fd, STDERR_FILENO) != STDERR_FILENO)
171 error = error ? error : err_dup2_failed_on_stderr;
172 }
173 } else {
174 // Parent Process
175 // Do nothing and let the pid get returned!
176 }
177 }
178 return pid;
179}
180

source code of lldb/tools/debugserver/source/PseudoTerminal.cpp