llvm-project/lldb/source/Utility/PseudoTerminal.cpp

//===-- PseudoTerminal.cpp --------------------------------------*- C++ -*-===//
//
//                     The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//

#include "lldb/Utility/PseudoTerminal.h"

#include <errno.h>
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#if defined(TIOCSCTTY)
#include <sys/ioctl.h>
#endif

using namespace lldb_utility;

//----------------------------------------------------------------------
// PseudoTerminal constructor
//----------------------------------------------------------------------
PseudoTerminal::PseudoTerminal () :
    m_master_fd(invalid_fd),
    m_slave_fd(invalid_fd)
{
}

//----------------------------------------------------------------------
// Destructor
//
// The destructor will close the master and slave file descriptors
// if they are valid and ownwership has not been released using the
// ReleaseMasterFileDescriptor() or the ReleaseSaveFileDescriptor()
// member functions.
//----------------------------------------------------------------------
PseudoTerminal::~PseudoTerminal ()
{
    CloseMasterFileDescriptor();
    CloseSlaveFileDescriptor();
}

//----------------------------------------------------------------------
// Close the master file descriptor if it is valid.
//----------------------------------------------------------------------
void
PseudoTerminal::CloseMasterFileDescriptor ()
{
    if (m_master_fd >= 0)
    {
        ::close (m_master_fd);
        m_master_fd = invalid_fd;
    }
}

//----------------------------------------------------------------------
// Close the slave file descriptor if it is valid.
//----------------------------------------------------------------------
void
PseudoTerminal::CloseSlaveFileDescriptor ()
{
    if (m_slave_fd >= 0)
    {
        ::close (m_slave_fd);
        m_slave_fd = invalid_fd;
    }
}

//----------------------------------------------------------------------
// Open the first available pseudo terminal with OFLAG as the
// permissions. The file descriptor is stored in this object and can
// be accessed with the MasterFileDescriptor() accessor. The
// ownership of the master file descriptor can be released using
// the ReleaseMasterFileDescriptor() accessor. If this object has
// a valid master files descriptor when its destructor is called, it
// will close the master file descriptor, therefore clients must
// call ReleaseMasterFileDescriptor() if they wish to use the master
// file descriptor after this object is out of scope or destroyed.
//
// RETURNS:
//  Zero when successful, non-zero indicating an error occurred.
//----------------------------------------------------------------------
bool
PseudoTerminal::OpenFirstAvailableMaster (int oflag, char *error_str, size_t error_len)
{
    if (error_str)
        error_str[0] = '\0';

    // Open the master side of a pseudo terminal
    m_master_fd = ::posix_openpt (oflag);
    if (m_master_fd < 0)
    {
        if (error_str)
            ::strerror_r (errno, error_str, error_len);
        return false;
    }

    // Grant access to the slave pseudo terminal
    if (::grantpt (m_master_fd) < 0)
    {
        if (error_str)
            ::strerror_r (errno, error_str, error_len);
        CloseMasterFileDescriptor ();
        return false;
    }

    // Clear the lock flag on the slave pseudo terminal
    if (::unlockpt (m_master_fd) < 0)
    {
        if (error_str)
            ::strerror_r (errno, error_str, error_len);
        CloseMasterFileDescriptor ();
        return false;
    }

    return true;
}

//----------------------------------------------------------------------
// Open the slave pseudo terminal for the current master pseudo
// terminal. A master pseudo terminal should already be valid prior to
// calling this function (see OpenFirstAvailableMaster()).
// The file descriptor is stored this object's member variables and can
// be accessed via the GetSlaveFileDescriptor(), or released using the
// ReleaseSlaveFileDescriptor() member function.
//
// RETURNS:
//  Zero when successful, non-zero indicating an error occurred.
//----------------------------------------------------------------------
bool
PseudoTerminal::OpenSlave (int oflag, char *error_str, size_t error_len)
{
    if (error_str)
        error_str[0] = '\0';

    CloseSlaveFileDescriptor();

    // Open the master side of a pseudo terminal
    const char *slave_name = GetSlaveName (error_str, error_len);

    if (slave_name == NULL)
        return false;

    m_slave_fd = ::open (slave_name, oflag);

    if (m_slave_fd < 0)
    {
        if (error_str)
            ::strerror_r (errno, error_str, error_len);
        return false;
    }

    return true;
}



//----------------------------------------------------------------------
// Get the name of the slave pseudo terminal. A master pseudo terminal
// should already be valid prior to calling this function (see
// OpenFirstAvailableMaster()).
//
// RETURNS:
//  NULL if no valid master pseudo terminal or if ptsname() fails.
//  The name of the slave pseudo terminal as a NULL terminated C string
//  that comes from static memory, so a copy of the string should be
//  made as subsequent calls can change this value.
//----------------------------------------------------------------------
const char*
PseudoTerminal::GetSlaveName (char *error_str, size_t error_len) const
{
    if (error_str)
        error_str[0] = '\0';

    if (m_master_fd < 0)
    {
        if (error_str)
            ::snprintf (error_str, error_len, "%s", "master file descriptor is invalid");
        return NULL;
    }
    const char *slave_name = ::ptsname (m_master_fd);

    if (error_str && slave_name == NULL)
        ::strerror_r (errno, error_str, error_len);

    return slave_name;
}


//----------------------------------------------------------------------
// Fork a child process and have its stdio routed to a pseudo terminal.
//
// In the parent process when a valid pid is returned, the master file
// descriptor can be used as a read/write access to stdio of the
// child process.
//
// In the child process the stdin/stdout/stderr will already be routed
// to the slave pseudo terminal and the master file descriptor will be
// closed as it is no longer needed by the child process.
//
// This class will close the file descriptors for the master/slave
// when the destructor is called, so be sure to call
// ReleaseMasterFileDescriptor() or ReleaseSlaveFileDescriptor() if any
// file descriptors are going to be used past the lifespan of this
// object.
//
// RETURNS:
//  in the parent process: the pid of the child, or -1 if fork fails
//  in the child process: zero
//----------------------------------------------------------------------
lldb::pid_t
PseudoTerminal::Fork (char *error_str, size_t error_len)
{
    if (error_str)
        error_str[0] = '\0';

    pid_t pid = LLDB_INVALID_PROCESS_ID;
    if (OpenFirstAvailableMaster (O_RDWR, error_str, error_len))
    {
        // Successfully opened our master pseudo terminal

        pid = ::fork ();
        if (pid < 0)
        {
            // Fork failed
            if (error_str)
            ::strerror_r (errno, error_str, error_len);
        }
        else if (pid == 0)
        {
            // Child Process
            ::setsid();

            if (OpenSlave (O_RDWR, error_str, error_len))
            {
                // Successfully opened slave
                // We are done with the master in the child process so lets close it
                CloseMasterFileDescriptor ();

#if defined(TIOCSCTTY)
                // Acquire the controlling terminal
                if (::ioctl (m_slave_fd, TIOCSCTTY, (char *)0) < 0)
                {
                    if (error_str)
                        ::strerror_r (errno, error_str, error_len);
                }
#endif
                // Duplicate all stdio file descriptors to the slave pseudo terminal
                if (::dup2 (m_slave_fd, STDIN_FILENO) != STDIN_FILENO)
                {
                    if (error_str && !error_str[0])
                        ::strerror_r (errno, error_str, error_len);
                }

                if (::dup2 (m_slave_fd, STDOUT_FILENO) != STDOUT_FILENO)
                {
                    if (error_str && !error_str[0])
                        ::strerror_r (errno, error_str, error_len);
                }

                if (::dup2 (m_slave_fd, STDERR_FILENO) != STDERR_FILENO)
                {
                    if (error_str && !error_str[0])
                        ::strerror_r (errno, error_str, error_len);
                }
            }
        }
        else
        {
            // Parent Process
            // Do nothing and let the pid get returned!
        }
    }
    return pid;
}

//----------------------------------------------------------------------
// The master file descriptor accessor. This object retains ownership
// of the master file descriptor when this accessor is used. Use
// ReleaseMasterFileDescriptor() if you wish this object to release
// ownership of the master file descriptor.
//
// Returns the master file descriptor, or -1 if the master file
// descriptor is not currently valid.
//----------------------------------------------------------------------
int
PseudoTerminal::GetMasterFileDescriptor () const
{
    return m_master_fd;
}

//----------------------------------------------------------------------
// The slave file descriptor accessor.
//
// Returns the slave file descriptor, or -1 if the slave file
// descriptor is not currently valid.
//----------------------------------------------------------------------
int
PseudoTerminal::GetSlaveFileDescriptor () const
{
    return m_slave_fd;
}

//----------------------------------------------------------------------
// Release ownership of the master pseudo terminal file descriptor
// without closing it. The destructor for this class will close the
// master file descriptor if the ownership isn't released using this
// call and the master file descriptor has been opened.
//----------------------------------------------------------------------
int
PseudoTerminal::ReleaseMasterFileDescriptor ()
{
    // Release ownership of the master pseudo terminal file
    // descriptor without closing it. (the destructor for this
    // class will close it otherwise!)
    int fd = m_master_fd;
    m_master_fd = invalid_fd;
    return fd;
}

//----------------------------------------------------------------------
// Release ownership of the slave pseudo terminal file descriptor
// without closing it. The destructor for this class will close the
// slave file descriptor if the ownership isn't released using this
// call and the slave file descriptor has been opened.
//----------------------------------------------------------------------
int
PseudoTerminal::ReleaseSlaveFileDescriptor ()
{
    // Release ownership of the slave pseudo terminal file
    // descriptor without closing it (the destructor for this
    // class will close it otherwise!)
    int fd = m_slave_fd;
    m_slave_fd = invalid_fd;
    return fd;
}