source: trunk/user/ksh/ksh.c @ 587

/////////////////////////////////////////////////////////////////////////////////////////
// File   :  ksh.c
// Date   :  October 2017
// Author :  Alain Greiner
/////////////////////////////////////////////////////////////////////////////////////////
// This application implements a minimal shell for ALMOS-MKH.
//
// This user KSH process contains two POSIX threads:
// - the "main" thread contains the infinite loop implementing
//   the children processes termination monitoring, using the wait() syscall.
// - the "interactive" thread contains the infinite loop implementing the command
//   interpreter attached to the TXT terminal, and handling one KSH command
//   per iteration. 
//
// The children processes are created by the <load> command, and are
// attached to the same TXT terminal as the KSH process itself.
// A child process can be lauched in foreground or in background: 
// . when the child process is running in foreground, the KSH process loses
//   the TXT terminal ownership, that is transfered to the child process.
// . when the child process is running in background: the KSH process keeps
//   the TXT terminal ownership.
//
// A semaphore is used to synchronize the two KSH threads. At each iteration, 
// the interactive thread check the semaphore (with a sem_wait). It blocks 
// and deschedules, if the KSH process loosed the TXT ownership (after a load,
// or for any other cause. It unblocks with the following policy:
// . if the command is "not a load", the semaphore is incremented by the 
//   cmd_***() function when the command is completed, to allow the KSH interactive()
//   function to get the next command in the while loop.    
// . if the command is a "load without &", the TXT is given to the NEW process by the
//   execve() syscall, and is released to the KSH process when NEW process terminates.
//   The KSH process is notified and the KSH main() function increments the semahore 
//   to allow the KSH interactive() function to handle commands.
// . if the command is a "load with &", the cmd_load() function returns the TXT 
//   to the KSH process and increment the semaphore, when the parent KSH process 
//   returns from the fork() syscall.
/////////////////////////////////////////////////////////////////////////////////////////

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <sys/wait.h>
#include <signal.h>
#include <unistd.h>
#include <almosmkh.h>
#include <semaphore.h>

#define CMD_MAX_SIZE   (256)    // max number of characters in one command
#define LOG_DEPTH      (32)     // max number of registered commands 
#define MAX_ARGS           (32)     // max number of arguments in a command

#define MAIN_DEBUG          0
#define CMD_LOAD_DEBUG      0

//////////////////////////////////////////////////////////////////////////////////////////
//         Structures
//////////////////////////////////////////////////////////////////////////////////////////

// one entry in the registered commands array
typedef struct log_entry_s 
{
        char          buf[CMD_MAX_SIZE];
        unsigned int  count;
}
log_entry_t;

// one entry in the supported command types array
typedef struct ksh_cmd_s 
{
        char * name;
        char * desc;
        void   (*fn)( int , char ** );
}
ksh_cmd_t;


//////////////////////////////////////////////////////////////////////////////////////////
//         Global Variables
//////////////////////////////////////////////////////////////////////////////////////////

ksh_cmd_t       cmd[];                    // array of supported commands

log_entry_t     log_entries[LOG_DEPTH];   // array of registered commands

unsigned int    ptw;                      // write pointer in log_entries[]
unsigned int    ptr;                      // read pointer in log_entries[]

pthread_attr_t  attr;                     // interactive thread attributes

sem_t           semaphore;                // block interactive thread when zero

//////////////////////////////////////////////////////////////////////////////////////////
//         Shell  Commands
//////////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////
static void cmd_cat( int argc , char **argv )
{
        char         * path;

        if (argc != 2) 
    {
                printf("  usage: cat pathname\n");
                return;
        }

        path = argv[1];

    printf("  error: not implemented yet\n", argc, argv );

/*
        // open the file
        fd = open( path , O_RDONLY , 0 );
        if (fd < 0) 
    {
                printf("  error: cannot open %s\n", path);
                goto exit;
        }

        // get file size 
        if (stat(path, &st) == -1)
    {
                printf("  error: cannot stat %s\n", path);
                goto exit;
        }
        if (S_ISDIR(st.st_mode)) {
                printf("  error: %s is a directory\n", path);
                goto exit;
        }
        size = st.st_size;

        // mmap the file 
        buf = mmap(NULL, size, PROT_READ|PROT_WRITE, MAP_PRIVATE, fd, 0);
        if (buf == NULL || buf == (char *)-1) {
                printf("  error: cannot map %s\n", path);
                goto exit;
        }

        // set terminating '0'
        buf[size-1] = 0;

        // display the file content
        printf("%s", buf);

exit:
        if (buf != NULL) munmap(buf, size);
        if (fd >= 0) close(fd);
*/

    // release semaphore to get next command
    sem_post( &semaphore );

}   // end cmd_cat()

////////////////////////////////////////////
static void cmd_cd( int argc , char **argv )
{
        char * path;

        if (argc != 2)
    {
                printf("  usage: cd pathname\n");
                return;
        }

        path = argv[1];

    printf("  error: not implemented yet\n", argc, argv );

    // release semaphore to get next command
    sem_post( &semaphore );

}   // end cmd_cd()

/////////////////////////////////////////
static void cmd_cp(int argc, char **argv)
{
//      int src_fd = -1, dst_fd = -1;
//      char *srcpath, *dstpath;
//      struct stat st;
//      size_t size, i;
//      char buf[1024];

        if (argc != 3) 
    {
                printf("  usage: cp src_pathname dst_pathname\n");
                return;
        }

    printf("  error: not implemented yet\n", argc, argv );

/*
        srcpath = argv[1];
        dstpath = argv[2];

        // open the src file 
        src_fd = open(srcpath, O_RDONLY, 0);
        if (src_fd < 0) {
                printf("  error: cannot open %s / err = %d\n", srcpath, errno);
                goto exit;
        }

        // get file size 
        if (stat(srcpath, &st) == -1) {
                printf("  error: cannot stat %s\n", srcpath);
                goto exit;
        }
        if (S_ISDIR(st.st_mode)) {
                printf("  error: %s is a directory\n", srcpath);
                goto exit;
        }
        size = st.st_size;

        // open the dst file 
        dst_fd = open(dstpath, O_CREAT|O_TRUNC|O_RDWR, 0);
        if (dst_fd < 0) {
                printf("  error: cannot open %s / err = %d\n", dstpath, errno);
                goto exit;
        }
        if (stat(dstpath, &st) == -1) {
                printf("  error: cannot stat %s\n", dstpath);
                goto exit;
        }
        if (S_ISDIR(st.st_mode)) {
                printf("  error: %s is a directory\n", dstpath);
                goto exit;
        }

        i = 0;
        while (i < size)
        {
                size_t rlen = (size - i < 1024 ? size - i : 1024);
                size_t wlen;
                ssize_t ret;

                // read the source 
                ret = read(src_fd, buf, rlen);
                if (ret == -1) {
                        printf("  error: cannot read from file %s\n", srcpath);
                        goto exit;
                }
                rlen = (size_t)ret;

                // write to the destination 
                ret = write(dst_fd, buf, rlen);
                if (ret == -1) {
                        printf("  error: cannot write to file %s\n", dstpath);
                        goto exit;
                }
                wlen = (size_t)ret;

                // check 
                if (wlen != rlen) {
                        printf("  error: cannot write on device\n");
                        goto exit;
                }

                i += rlen;
        }

exit:
        if (src_fd >= 0) close(src_fd);
        if (dst_fd >= 0) close(dst_fd);
*/

    // release semaphore to get next command
    sem_post( &semaphore );

}   // end cmd_cp()

/////////////////////////////////////////////////
static void cmd_display( int argc , char **argv )
{
    unsigned int  cxy;
    unsigned int  lid;
    unsigned int  pid;
    unsigned int  txt_id;

    if( strcmp( argv[1] , "vmm" ) == 0 )
    {
        if( argc != 4 )
        {
                    printf("  usage: display vmm cxy pid\n");
                    return;
            }

            cxy = atoi(argv[2]);
            pid = atoi(argv[3]);

        if( display_vmm( cxy , pid ) )
        {
            printf("  error: no process %x in cluster %x\n", pid , cxy );
        }
    }
    else if( strcmp( argv[1] , "sched" ) == 0 )
    {
        if( argc != 4 )
        {
                    printf("  usage: display sched cxy lid\n");
                    return;
            }

            cxy = atoi(argv[2]);
            lid = atoi(argv[3]);

        if( display_sched( cxy , lid ) )
        {
            printf("  error: illegal arguments cxy = %x / lid = %d\n", cxy, lid );
        }
    }
    else if( strcmp( argv[1] , "process" ) == 0 )
    {
        if( argc != 3 )
        {
                    printf("  usage: display process cxy\n");
                    return;
            }

            cxy = atoi(argv[2]);

        if( display_cluster_processes( cxy ) )
        {
            printf("  error: illegal argument cxy = %x\n", cxy );
        }
    }
    else if( strcmp( argv[1] , "txt" ) == 0 )
    {
        if( argc != 3 )
        {
                    printf("  usage: display txt txt_id\n");
                    return;
            }

            txt_id = atoi(argv[2]);

        if( display_txt_processes( txt_id ) )
        {
            printf("  error: illegal argument txt_id = %d\n", txt_id );
        }
    }
    else if( strcmp( argv[1] , "vfs" ) == 0 )
    {
        if( argc != 2 )
        {
                    printf("  usage: display vfs\n");
                    return;
            }

        display_vfs();
    }
    else if( strcmp( argv[1] , "chdev" ) == 0 )
    {
        if( argc != 2 )
        {
                    printf("  usage: display chdev\n");
                    return;
            }

        display_chdev();
    }
    else if( strcmp( argv[1] , "dqdt" ) == 0 )
    {
        if( argc != 2 )
        {
                    printf("  usage: display dqdt\n");
                    return;
            }

        display_dqdt();
    }
    else
    {
        printf("  usage: display (vmm/sched/process/vfs/chdev/txt) [arg2] [arg3]\n");
    }

    // release semaphore to get next command
    sem_post( &semaphore );

} // end cmd_display()

/////////////////////////////////////////
static void cmd_fg(int argc, char **argv)
{
        unsigned int pid;

        if (argc != 2) 
    {
                printf("  usage: %s pid\n", argv[0]);
                return;
        }

    pid = atoi( argv[1] );   

    if( pid == 0 )
    {
                printf("  error: PID cannot be 0\n" );
        }

    if( fg( pid ) )
    {
                printf("  error: cannot find process %x\n", pid );
        }

    // release semaphore to get next command
    sem_post( &semaphore );

}  // end cmd_fg()

//////////////////////////////////////////////
static void cmd_help( int argc , char **argv )
{
        unsigned int i;

        if (argc != 1) 
    {
                printf("  usage: %s\n", argv[0]);
                return;
        }

        printf("available commands:\n");
        for (i = 0 ; cmd[i].name ; i++) 
    {
                printf("\t%s\t : %s\n", cmd[i].name , cmd[i].desc);
        }

    // release semaphore to get next command
    sem_post( &semaphore );

}   // end cmd_help()

//////////////////////////////////////////////
static void cmd_kill( int argc , char **argv )
{
        unsigned int pid;

        if (argc != 2) 
    {
                printf("  usage: %s pid\n", argv[0]);
                return;
        }

        pid = atoi( argv[1] );

    if( pid == 0 )
    {
                printf("  error: kernel process 0 cannot be killed\n" );
        }

        if( kill( pid , SIGKILL ) )
    {
                printf("  error: process %x cannot be killed\n", pid );
        }

    // release semaphore to get next command
    sem_post( &semaphore );

}   // end cmd_kill()

//////////////////////////////////////////////
static void cmd_load( int argc , char **argv )
{
        int                  ret_fork;           // return value from fork 
        int                  ret_exec;           // return value from exec
    unsigned int         ksh_pid;            // KSH process PID
        char               * pathname;           // path to .elf file
    unsigned int         background;         // background execution if non zero

        if( (argc < 2) || (argc > 3) )  
    {
                printf("  usage: %s pathname [&] / argc = %d\n", argv[0], argc );  // @@@
                return;
        }

        pathname = argv[1];

    if( argc == 3 ) background = (argv[2][0] == '&');
    else            background = 0;

    // get KSH process PID
    ksh_pid = getpid();

#if CMD_LOAD_DEBUG
long long unsigned cycle;
get_cycle( &cycle );
printf("\n@@@ %s : KSH PID %x before fork / path %s / background %d / cycle %d\n",
__FUNCTION__, ksh_pid, argv[1], background, (int)cycle );
#endif

    // KSH process fork CHILD process
        ret_fork = fork();

    if ( ret_fork < 0 )     // it is a failure reported to KSH
    {
        printf("  error: ksh process unable to fork\n");
        return;
    }
    else if (ret_fork == 0) // it is the CHILD process 
    {

#if CMD_LOAD_DEBUG
get_cycle( &cycle );
printf("\n@@@ %s : CHILD_PID %x after fork, before exec / cycle %d\n",
__FUNCTION__ , getpid(), (int)cycle );
#endif

        // CHILD process exec NEW process
        ret_exec = execve( pathname , NULL , NULL );

#if CMD_LOAD_DEBUG
get_cycle( &cycle );
printf("\n@@@ %s : CHILD_PID %x after exec / ret_exec %d / cycle %d\n",
__FUNCTION__ , getpid(), ret_exec, (int)cycle );
#endif

        // this is only executed in case of exec failure
        if( ret_exec )
        {
            printf("  error: child process unable to exec <%s>\n", pathname );
            exit( 0 );
        }   
        } 
    else                    // it is the KSH process : ret_fork is the new process PID
    {

#if CMD_LOAD_DEBUG
get_cycle( &cycle );
printf("\n@@@ %s : KSH_PID %x after fork / ret_fork %x / cycle %d\n",
__FUNCTION__, getpid(), ret_fork, (int)cycle );
#endif

        if( background )    // child in background =>  KSH must keep TXT ownership
        {
            // execve() tranfered TXT ownership to child => give it back to KSH
            fg( ksh_pid );

            // release semaphore to get next command
            sem_post( &semaphore );
        }
    }
}   // end cmd_load

/////////////////////////////////////////////
static void cmd_log( int argc , char **argv )
{
        unsigned int i;

        if (argc != 1)
    {
                printf("  usage: %s\n", argv[0], argc ); 
                return;
        }

        printf("--- registered commands ---\n");
        for (i = 0; i < LOG_DEPTH; i++) 
    {
                printf(" - %d\t: %s\n", i, &log_entries[i].buf);
        }

    // release semaphore to get next command
    sem_post( &semaphore );

} // end cmd_log()


////////////////////////////////////////////
static void cmd_ls( int argc , char **argv )
{
        char  * path;

//  struct dirent * file;
//  DIR *dir;

        if (argc == 1)
    {
                path = ".";
        }
    else if (argc == 2) 
    {
                path = argv[1];
        } 
    else 
    {
                printf("  usage: ls [path]\n");
                return;
        }

    printf("  error: not implemented yet\n");
/*
        dir = opendir( path );
        while ((file = readdir(dir)) != NULL)
        {
                printf(" %s\n", file->d_name);
        }
        closedir(dir);
*/

    // release semaphore to get next command
    sem_post( &semaphore );

} // end cmd_ls()

///////////////////////////////////////////////
static void cmd_mkdir( int argc , char **argv )
{
        char * pathname;

        if (argc != 2)
    {
                printf("  usage: mkdir pathname\n");
                return;
        }

    pathname = argv[1];

    printf("  error: not implemented yet\n");

    // release semaphore to get next command
    sem_post( &semaphore );

} // end cmd_mkdir()

////////////////////////////////////////////
static void cmd_mv( int argc , char **argv )
{

        if (argc < 3)
        {
                printf("  usage : %s src_pathname dst_pathname\n", argv[0]);
                return;
        }

    printf("  error: not implemented yet\n");
    
    // release semaphore to get next command
    sem_post( &semaphore );

}  // end cmd_mv

/////////////////////////////////////////////
static void cmd_pwd( int argc , char **argv )
{
        char buf[1024];

        if (argc != 1)
    {
                printf("  usage: %s\n", argv[0]);
                return;
        }

        if ( getcwd( buf , 1024 ) ) 
    {
                printf("  error: unable to get current directory\n");
        }
    else 
    {
                printf("%s\n", buf);
        }

    // release semaphore to get next command
    sem_post( &semaphore );

}  // end cmd_pwd()

////////////////////////////////////////////
static void cmd_rm( int argc , char **argv )
{
        char * pathname;

        if (argc != 2)
    {
                printf("  usage: %s pathname\n", argv[0]);
                return;
        }

        pathname = argv[1];

    printf("  error: not implemented yet\n");

    // release semaphore to get next command
    sem_post( &semaphore );

}  // end_cmd_rm()

///////////////////////////////////////////////
static void cmd_rmdir( int argc , char **argv )
{
    // same as cmd_rm()
        cmd_rm(argc, argv);
}

///////////////////////////////////////////////
static void cmd_trace( int argc , char **argv )
{
    unsigned int cxy;
    unsigned int lid;

        if (argc != 3)
    {
                printf("  usage: trace cxy lid \n");
                return;
        }

    cxy = atoi(argv[1]);
    lid = atoi(argv[2]);

    if( trace( 1 , cxy , lid ) )
    {
        printf("  error: core[%x,%d] not found\n", cxy, lid );
    }

    // release semaphore to get next command
    sem_post( &semaphore );

}  // end cmd_trace

///////////////////////////////////////////////
static void cmd_untrace( int argc , char **argv )
{
    unsigned int cxy;
    unsigned int lid;

        if (argc != 3)
    {
                printf("  usage: untrace cxy lid \n");
                return;
        }

    cxy = atoi(argv[1]);
    lid = atoi(argv[2]);

    if( trace( 0 , cxy , lid ) )
    {
        printf("  error: core[%x,%d] not found\n", cxy, lid );
    }

    // release semaphore to get next command
    sem_post( &semaphore );

}  // end cmd_untrace()

///////////////////////////////////////////////////////////////////////////////////
// Array of commands
///////////////////////////////////////////////////////////////////////////////////

ksh_cmd_t cmd[] =
{
        { "cat",     "display file content",                            cmd_cat     },
        { "cd",      "change current directory",                        cmd_cd      },
        { "cp",      "replicate a file in file system",                 cmd_cp      },
    { "fg",      "put a process in foreground",                     cmd_fg      },
    { "display", "display vmm/sched/process/vfs/chdev/txt",         cmd_display },
        { "load",    "load an user application",                        cmd_load    },
        { "help",    "list available commands",                         cmd_help    },
        { "kill",    "kill a process (all threads)",                    cmd_kill    },
        { "log",     "list registered commands",                        cmd_log     },
        { "ls",      "list directory entries",                          cmd_ls      },
        { "mkdir",   "create a new directory",                          cmd_mkdir   },
        { "mv",      "move a file in file system",                      cmd_mv      },
        { "pwd",     "print current working directory",                 cmd_pwd     },
        { "rm",      "remove a file from file system",                  cmd_rm      },
        { "rmdir",   "remove a directory from file system",             cmd_rmdir   },
        { "trace",   "activate trace for a given core",                 cmd_trace   },
        { "untrace", "desactivate trace for a given core",              cmd_untrace },
        { NULL,      NULL,                                                                              NULL        }
};

////////////////////////////////////////////////////////////////////////////////////
// This function analyses one command (with arguments), executes it, and returns.
////////////////////////////////////////////////////////////////////////////////////
static void __attribute__ ((noinline)) parse( char * buf )
{
        int argc = 0;
        char *argv[MAX_ARGS];
        int i;
        int len = strlen(buf);

        // build argc/argv
        for (i = 0; i < len; i++) 
    {
                if (buf[i] == ' ') 
        {
                        buf[i] = '\0';
                }
        else if (i == 0 || buf[i - 1] == '\0') 
        {
                        if (argc < MAX_ARGS) 
            {
                                argv[argc] = &buf[i];
                                argc++;
                        }
                }
        }

    // analyse command type
        if (argc > 0)
    {
                int found = 0;

                argv[argc] = NULL;

                // try to match typed command 
                for (i = 0 ; cmd[i].name ; i++)
        {
                        if (strcmp(argv[0], cmd[i].name) == 0)
            {
                                cmd[i].fn(argc, argv);
                                found = 1;
                                break;
                        }
                }

                if (!found)  // undefined command
        {
                        printf("  error : undefined command <%s>\n", argv[0]);

            // release semaphore to get next command
            sem_post( &semaphore );
                }
        }
}  // end parse()

///////////////////////////////
static void interactive( void )
{
        char           c;                                               // read character
        char           buf[CMD_MAX_SIZE];               // buffer for one command
    unsigned int   end_command;             // last character found in a command
        unsigned int   count;                   // pointer in command buffer
        unsigned int   i;                                               // index for loops
        unsigned int   state;                   // escape sequence state

/* This can be used to simplify debug, as it avoids interactive mode

for( i=1 ; 1 ; i++ )
{
    if( sem_wait( &semaphore ) )
    {
        printf("\n[ksh error] cannot found semafore\n" );
        exit( 1 );
    }
    else
    {
        printf("\n[ksh] %d for fft\n", i );
    }
    strcpy( buf , "load /bin/user/fft.elf" );
    parse( buf );
}

*/

        enum fsm_states 
    {
                NORMAL = 0,
                ESCAPE = 1,
                BRAKET = 2,
        };

        // This lexical analyser writes one command line in the command buffer.
        // It is implemented as a 3 states FSM to handle the following escape sequences:
        // - ESC [ A : up arrow
        // - ESC [ B : down arrow
        // - ESC [ C : right arrow
        // - ESC [ D : left arrow
        // The three states have the following semantic:
        // - NORMAL : no (ESC) character has been found
        // - ESCAPE : the character (ESC) has been found
        // - BRAKET : the wo characters (ESC,[) have been found

    // external loop on the commands
    // the in teractive thread should not exit this loop
        while (1)
        {
            // initialize command buffer
            memset( buf, 0x20 , sizeof(buf) );   // TODO useful ?
            count = 0;
            state = NORMAL;

        // decrement semaphore, and block if the KSH process is not the TXT owner
        if ( sem_wait( &semaphore ) )
        {
            printf("\n[ksh error] cannot found semafore\n" );
            exit( 1 );
        }

        // display prompt on a new line
        printf("\n[ksh] ");
 
        end_command = 0;

        // internal loop on characters in one command
        while( end_command == 0 )
        {
            // get one character from TXT_RX
                c = (char)getchar();

            if( c == 0 ) continue;

                    if( state == NORMAL )  // we are not in an escape sequence
                    {
                                if ((c == '\b') || (c == 0x7F))  // backspace => remove one character
                                {
                                    if (count > 0)
                    {
                                        printf("\b \b");
                                        count--;
                                    }
                                }
                                else if (c == '\n')                  // new line => end of command
                                {
                                    if (count > 0)               // analyse & execute command
                                    {
                                            // complete command with NUL character
                                            buf[count] = 0;
                        count++;

                                        // register command in log arrays
                                            strcpy(log_entries[ptw].buf, buf);
                                            log_entries[ptw].count = count;
                                            ptw = (ptw + 1) % LOG_DEPTH;
                                            ptr = ptw;

                        // echo character
                        putchar( c );

                                            // call parser to analyse and execute command
                                            parse( buf );
                                    }
                    else                         // no command registered
                    {
                        // release semaphore to get next command
                        sem_post( &semaphore );
                    }

                    // exit internal loop on characters
                    end_command = 1;
                }
                            else if (c == '\t')             // tabulation => do nothing
                                {
                            }
                            else if (c == (char)0x1B)       // ESC => start an escape sequence
                            {
                    state = ESCAPE;
                            }
                            else                                               // normal character
                                {
                                    if (count < sizeof(buf) - 1)
                                    {
                        // register character in command buffer
                                            buf[count] = c;
                                            count++;

                        // echo character
                        putchar( c );
                                        }
                                }
                        }
                        else if( state == ESCAPE )  
                        {
                                if (c == '[')           //  valid sequence => continue
                                {
                                        state = BRAKET;
                                }
                                else                               // invalid sequence => do nothing
                                {
                                        state = NORMAL;
                                }
                        }
                        else if( state == BRAKET )
                        {
                                if (c == 'D')   // valid  LEFT sequence => move buf pointer left
                                {
                                        if (count > 0)
                                        {
                                                printf("\b");
                                                count--;
                                        }

                                        // get next user char
                                        state = NORMAL;
                                }
                                else if (c == 'C')   // valid  RIGHT sequence => move buf pointer right
                                {
                                        if (count < sizeof(buf) - 1)
                                        {
                                                printf("%c", buf[count]);
                                                count++;
                                        }

                                        // get next user char
                                        state = NORMAL;
                                }
                                else if (c == 'A')   // valid  UP sequence => move log pointer backward
                                {
                                        // cancel current command
                                        for (i = 0; i < count; i++) printf("\b \b");
                                        count = 0;

                                        // copy log command into buf
                                        ptr = (ptr - 1) % LOG_DEPTH;
                                        strcpy(buf, log_entries[ptr].buf);
                                        count = log_entries[ptr].count - 1;

                                        // display log command
                                        printf("%s", buf);

                                        // get next user char
                                        state = NORMAL;
                                }
                                else if (c == 'B')   // valid  DOWN sequence => move log pointer forward
                                {
                                        // cancel current command
                                        for (i = 0 ; i < count; i++) printf("\b \b");
                                        count = 0;

                                        // copy log command into buf
                                        ptr = (ptr + 1) % LOG_DEPTH;
                                        strcpy(buf, log_entries[ptr].buf);
                                        count = log_entries[ptr].count;

                                        // display log command
                                        printf("%s", buf);

                                        // get next user char
                                        state = NORMAL;
                                }
                                else                               // other character => do nothing
                                {
                                        // get next user char
                                        state = NORMAL;
                                }
                        }
                }  // end internal while loop on characters
        }  // end external while loop on commands
}  // end interactive()

////////////////
int main( void )
{
    unsigned int cxy;             // owner cluster identifier for this KSH process
    unsigned int lid;             // core identifier for this KSH main thread
    int          status;          // child process termination status
    int          child_pid;       // child process identifier
    int          parent_pid;      // parent process identifier (i.e. this process)
    pthread_t    trdid;           // interactive thread identifier (unused)
    unsigned int is_owner;        // non-zero if KSH process is TXT owner

    // initialize log buffer
        memset( &log_entries , 0, sizeof(log_entries));
        ptw   = 0;
        ptr   = 0;

    // get KSH process pid and core
    parent_pid = getpid();
    get_core( &cxy , &lid );

#if MAIN_DEBUG
printf("\n[ksh] main started on core[%x,%d]\n", cxy , lid ); 
#endif
    
    // initializes the semaphore used to synchronize with interactive thread
    if ( sem_init( &semaphore , 0 , 1 ) )
    {
        printf("\n[KSH ERROR] cannot initialize semaphore\n" );
        exit( 1 ); 
    }

#if MAIN_DEBUG
printf("\n[ksh] main initialized semaphore\n" ); 
#endif
    
    // initialize interactive thread attributes
    attr.attributes = PT_ATTR_DETACH | PT_ATTR_CLUSTER_DEFINED;
    attr.cxy        = cxy;

    // lauch the interactive thread 
    pthread_create( &trdid,
                    &attr,
                    &interactive,   // entry function
                    NULL ); 
#if MAIN_DEBUG
printf("\n[ksh] main launched interactive thread => wait children termination\n" ); 
#endif
    
    // enter infinite loop monitoring children processes termination 
    while( 1 )
    {
        // wait children termination
        child_pid = wait( &status );

#if MAIN_DEBUG
if( WIFEXITED  (status) ) printf("\n[ksh] child process %x exit\n"   , child_pid );
if( WIFSIGNALED(status) ) printf("\n[ksh] child process %x killed\n" , child_pid );
if( WIFSTOPPED (status) ) printf("\n[ksh] child process %x stopped\n", child_pid );
#endif

        // release semaphore if KSH process is TXT owner, to unblock interactive thread
        is_fg( parent_pid , &is_owner );
        if( is_owner ) sem_post( &semaphore );

    }
}  // end main()