source: trunk/kernel/kern/process.c @ 407

/*
 * process.c - process related management
 *
 * Authors  Ghassan Almaless (2008,2009,2010,2011,2012)
 *          Mohamed Lamine Karaoui (2015)
 *          Alain Greiner (2016,2017)
 *
 * Copyright (c) UPMC Sorbonne Universites
 *
 * This file is part of ALMOS-MKH..
 *
 * ALMOS-MKH is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation; version 2.0 of the License.
 *
 * ALMOS-MKH is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with ALMOS-MKH; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <kernel_config.h>
#include <hal_types.h>
#include <hal_remote.h>
#include <hal_uspace.h>
#include <errno.h>
#include <printk.h>
#include <memcpy.h>
#include <bits.h>
#include <kmem.h>
#include <page.h>
#include <vmm.h>
#include <vfs.h>
#include <core.h>
#include <thread.h>
#include <list.h>
#include <string.h>
#include <scheduler.h>
#include <remote_spinlock.h>
#include <dqdt.h>
#include <cluster.h>
#include <ppm.h>
#include <boot_info.h>
#include <process.h>
#include <elf.h>
#include <syscalls.h>

//////////////////////////////////////////////////////////////////////////////////////////
// Extern global variables
//////////////////////////////////////////////////////////////////////////////////////////

extern process_t process_zero;

//////////////////////////////////////////////////////////////////////////////////////////
// Process initialisation related functions
//////////////////////////////////////////////////////////////////////////////////////////

///////////////////////////
process_t * process_alloc()
{
        kmem_req_t   req;

    req.type  = KMEM_PROCESS;
        req.size  = sizeof(process_t);
        req.flags = AF_KERNEL;

    return (process_t *)kmem_alloc( &req );
}

////////////////////////////////////////
void process_free( process_t * process )
{
    kmem_req_t  req;

        req.type = KMEM_PROCESS;
        req.ptr  = process;
        kmem_free( &req );
}

/////////////////////////////////////////////////
void process_reference_init( process_t * process,
                             pid_t       pid,
                             xptr_t      parent_xp )
{
    cxy_t       parent_cxy;
    process_t * parent_ptr;
    pid_t       parent_pid;

        error_t     error1;
        error_t     error2;
        error_t     error3;
    xptr_t      stdin_xp;
    xptr_t      stdout_xp;
    xptr_t      stderr_xp;
    uint32_t    stdin_id;
    uint32_t    stdout_id;
    uint32_t    stderr_id;

process_dmsg("\n[DBG] %s : core[%x,%d] enters for process %x\n",
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , pid );

    // get parent process cluster, local pointer, and pid
    // for all processes other than kernel process
    if( process == &process_zero )                   // kernel process
    {
        assert( (pid == 0) , __FUNCTION__ , "process_zero must have PID = 0\n");

        parent_cxy = 0;
        parent_ptr = NULL;
        parent_pid = 0;      
    }
    else                                             // user process
    {
        parent_cxy = GET_CXY( parent_xp );
        parent_ptr = (process_t *)GET_PTR( parent_xp );
        parent_pid = hal_remote_lw( XPTR( parent_cxy , &parent_ptr->pid ) );
    }

    // initialize PID, PPID, and REF
        process->pid    = pid;
    process->ppid   = parent_pid;
    process->ref_xp = XPTR( local_cxy , process );

    // initialize vmm, fd array and others structures for user processes.
    // These structures are not used by the kernel process.
    if( pid )
    {
        // initialize vmm (not for kernel)
        vmm_init( process );

process_dmsg("\n[DBG] %s : core[%x,%d] / vmm initialised for process %x\n", 
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , pid );

        // initialize fd_array (not for kernel)
        process_fd_init( process );

        // create stdin / stdout / stderr pseudo-files (not for kernel)
        if( parent_pid == 0 )                                              // process_init
        {
            error1 = vfs_open( process,
                               CONFIG_INIT_STDIN,
                               O_RDONLY, 
                               0,                // FIXME chmod
                               &stdin_xp, 
                               &stdin_id );

            error2 = vfs_open( process,
                               CONFIG_INIT_STDOUT,
                               O_WRONLY, 
                               0,                // FIXME chmod
                               &stdout_xp, 
                               &stdout_id );

            error3 = vfs_open( process,
                               CONFIG_INIT_STDERR,
                               O_WRONLY, 
                               0,                // FIXME chmod
                               &stderr_xp, 
                               &stderr_id );
        }
        else                                                               // user process
        {
            error1 = vfs_open( process,
                               CONFIG_USER_STDIN,
                               O_RDONLY, 
                               0,                // FIXME chmod
                               &stdin_xp, 
                               &stdin_id );

            error2 = vfs_open( process,
                               CONFIG_USER_STDOUT,
                               O_WRONLY, 
                               0,                // FIXME chmod
                               &stdout_xp, 
                               &stdout_id );

            error3 = vfs_open( process,
                               CONFIG_USER_STDERR,
                               O_WRONLY, 
                               0,                // FIXME chmod
                               &stderr_xp, 
                               &stderr_id );
        }

        assert( ((error1 == 0) && (error2 == 0) && (error3 == 0)) , __FUNCTION__ ,
        "cannot open stdin/stdout/stderr pseudo files\n");

        assert( ((stdin_id == 0) && (stdout_id == 1) && (stderr_id == 2)) , __FUNCTION__ ,
        "bad indexes : stdin %d / stdout %d / stderr %d \n", stdin_id , stdout_id , stderr_id );

process_dmsg("\n[DBG] %s : core[%x,%d] / fd array initialised for process %x\n", 
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , pid );


        // reset reference process files structures and cwd_lock (not for kernel)
            process->vfs_root_xp     = XPTR_NULL;
            process->vfs_bin_xp      = XPTR_NULL;
            process->vfs_cwd_xp      = XPTR_NULL;
        remote_rwlock_init( XPTR( local_cxy , &process->cwd_lock ) );

        // reset children list root (not for kernel)
        xlist_root_init( XPTR( local_cxy , &process->children_root ) );
            process->children_nr     = 0;

        // reset semaphore / mutex / barrier / condvar list roots (nor for kernel)
        xlist_root_init( XPTR( local_cxy , &process->sem_root ) );
        xlist_root_init( XPTR( local_cxy , &process->mutex_root ) );
        xlist_root_init( XPTR( local_cxy , &process->barrier_root ) );
        xlist_root_init( XPTR( local_cxy , &process->condvar_root ) );
        remote_spinlock_init( XPTR( local_cxy , &process->sync_lock ) );

        // register new process in the parent children list (nor for kernel)
        xptr_t entry = XPTR( local_cxy  , &process->brothers_list );
        xptr_t root  = XPTR( parent_cxy , &parent_ptr->children_root );
        xlist_add_first( root , entry );
    }

    // reset th_tbl[] array as empty
    uint32_t i;
    for( i = 0 ; i < CONFIG_THREAD_MAX_PER_CLUSTER ; i++ )
        {
        process->th_tbl[i] = NULL;
    }
    process->th_nr  = 0;
    spinlock_init( &process->th_lock );

    // register new process descriptor in local cluster manager local_list
    cluster_process_local_link( process );

    // register new process descriptor in owner cluster manager copies_list
    cluster_process_copies_link( process );

    // initialize signal manager TODO [AG]

        hal_fence();

process_dmsg("\n[DBG] %s : core[%x,%d] exit for process %x\n",
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , pid );

}  // process_reference init()

/////////////////////////////////////////////////////
error_t process_copy_init( process_t * local_process,
                           xptr_t      reference_process_xp )
{
    // get reference process cluster and local pointer
    cxy_t       ref_cxy = GET_CXY( reference_process_xp );
    process_t * ref_ptr = (process_t *)GET_PTR( reference_process_xp );

    // set the pid, ppid, ref_xp fields in local process
    local_process->pid    = hal_remote_lw( XPTR( ref_cxy , &ref_ptr->pid ) );
    local_process->ppid   = hal_remote_lw( XPTR( ref_cxy , &ref_ptr->ppid ) );
    local_process->ref_xp = reference_process_xp;

process_dmsg("\n[DBG] %s : core[%x,%d] enters for process %x in cluster %x\n",
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , local_process->pid );

    // reset local process vmm
    vmm_init( local_process );

    // reset process file descriptors array
        process_fd_init( local_process );

    // reset vfs_root_xp / vfs_bin_xp / vfs_cwd_xp fields
    local_process->vfs_root_xp = hal_remote_lwd( XPTR( ref_cxy , &ref_ptr->vfs_root_xp ) );
    local_process->vfs_bin_xp  = hal_remote_lwd( XPTR( ref_cxy , &ref_ptr->vfs_bin_xp ) );
    local_process->vfs_cwd_xp  = XPTR_NULL;

    // reset children list root (not used in a process descriptor copy)
    xlist_root_init( XPTR( local_cxy , &local_process->children_root ) );
    local_process->children_nr   = 0;

    // reset brothers list (not used in a process descriptor copy)
    xlist_entry_init( XPTR( local_cxy , &local_process->brothers_list ) );

    // reset semaphores list root (not used in a process descriptor copy)
    xlist_root_init( XPTR( local_cxy , &local_process->sem_root ) );
    xlist_root_init( XPTR( local_cxy , &local_process->mutex_root ) );
    xlist_root_init( XPTR( local_cxy , &local_process->barrier_root ) );
    xlist_root_init( XPTR( local_cxy , &local_process->condvar_root ) );

    // reset th_tbl[] array as empty
    uint32_t i;
    for( i = 0 ; i < CONFIG_THREAD_MAX_PER_CLUSTER ; i++ )
        {
        local_process->th_tbl[i] = NULL;
    }
    local_process->th_nr  = 0;
    spinlock_init( &local_process->th_lock );

    // register new process descriptor in local cluster manager local_list
    cluster_process_local_link( local_process );

    // register new process descriptor in owner cluster manager copies_list
    cluster_process_copies_link( local_process );

    // initialize signal manager TODO [AG]

        hal_fence();

process_dmsg("\n[DBG] %s : core[%x,%d] exit for process %x in cluster %x\n",
__FUNCTION__ , local_cxy , CURRENT_THREAD->core->lid , local_process->pid );

    return 0;

} // end process_copy_init()

///////////////////////////////////////////
void process_destroy( process_t * process )
{
        if( process->th_nr != 0 )
    {
        panic("process %x in cluster %x has still active threads",
              process->pid , local_cxy );
    }

    // get local process manager pointer
    pmgr_t * pmgr = &LOCAL_CLUSTER->pmgr;

    // get the lock protecting the list of local process descriptors
    remote_spinlock_lock( XPTR( local_cxy , &pmgr->local_lock ) );

    // remove the process descriptor from local_list in local cluster manager
    xlist_unlink( XPTR( local_cxy , &process->local_list ) );

    // release the lock protecting the list of local process descriptors
    remote_spinlock_unlock( XPTR( local_cxy , &pmgr->local_lock ) );

    // get extended pointer on copies_lock in owner cluster manager
    cxy_t  owner_cxy    = CXY_FROM_PID( process->pid );
        lpid_t lpid         = LPID_FROM_PID( process->pid );
    xptr_t copies_lock  = XPTR( owner_cxy , &pmgr->copies_lock[lpid] );

    // remove the local process descriptor from copies_list
    remote_spinlock_lock( copies_lock );
    xlist_unlink( XPTR( local_cxy , &process->copies_list ) );
    remote_spinlock_unlock( copies_lock );

    // synchronize memory
        hal_fence();

    // From this point, the process descriptor is unreachable

    // close all open files and update dirty TODO [AG]

    // release signal manager TODO [AG]

    // Decrease refcount for bin file, root file and cwd file
        if( process->vfs_bin_xp  != XPTR_NULL ) vfs_file_count_down( process->vfs_bin_xp );
        if( process->vfs_root_xp != XPTR_NULL ) vfs_file_count_down( process->vfs_root_xp );
        if( process->vfs_cwd_xp  != XPTR_NULL ) vfs_file_count_down( process->vfs_cwd_xp );

    // Destroy VMM
    vmm_destroy( process );

        process_dmsg("\n[DBG] %s for pid %d / page_faults = %d\n",
                 __FUNCTION__ , process->pid, process->vmm.pgfault_nr );

}  // end process_destroy()

////////////////////////////////////////
void process_kill( process_t * process )
{
    thread_t     * thread;    // pointer on current thead descriptor
    uint32_t       ltid;      // index in process th_tbl
    uint32_t       count;     // thread counter

printk("\n@@@ %s enter\n", __FUNCTION__ );

    // get lock protecting th_tbl[]
    spinlock_lock( &process->th_lock );

    // first loop on threads to send the THREAD_SIG_KILL signal to all process threads
    // we use both "ltid" and "count" indexes, because it can exist "holes" in th_tbl
    for( ltid = 0 , count = 0  ;
         (ltid < CONFIG_THREAD_MAX_PER_CLUSTER) && (count < process->th_nr) ;
         ltid++ )
    {
        thread = process->th_tbl[ltid];

        if( thread != NULL )
        {
            thread_kill( thread );
            count++;
        }
    }

printk("\n@@@ %s : %d signal(s) sent\n", __FUNCTION__, count );

    // second loop on threads to wait acknowledge from scheduler,
    // unlink thread from process and parent thread, and release thread descriptor
    for( ltid = 0 , count = 0  ;
         (ltid < CONFIG_THREAD_MAX_PER_CLUSTER) && (count < process->th_nr) ;
         ltid++ )
    {
        thread = process->th_tbl[ltid];

        if( thread != NULL )
        {

printk("\n@@@ %s start polling at cycle %d\n", __FUNCTION__ , hal_time_stamp() );

            // poll the THREAD_SIG_KILL bit until reset
            while( thread->signals & THREAD_SIG_KILL ) asm volatile( "nop" );

printk("\n@@@ %s exit polling\n", __FUNCTION__ );

            // detach target thread from parent if attached
            if( (thread->flags & THREAD_FLAG_DETACHED) != 0 ) 
            thread_child_parent_unlink( thread->parent , XPTR( local_cxy , thread ) );

            // unlink thread from process
            process_remove_thread( thread );

            // release memory for thread descriptor
            thread_destroy( thread );

            count++;
        }
    }

printk("\n@@@ %s : %d ack(s) received\n", __FUNCTION__, count );

    // release lock protecting th_tbl[]
    spinlock_unlock( &process->th_lock );

    // release memory allocated for process descriptor
    process_destroy( process );

printk("\n[@@@] %s : core[%x,%d] exit\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid );

}  // end process_kill()

///////////////////////////////////////////////
process_t * process_get_local_copy( pid_t pid )
{
    error_t        error;
    process_t    * process_ptr;   // local pointer on process
    xptr_t         process_xp;    // extended pointer on process

    cluster_t * cluster = LOCAL_CLUSTER;

    // get lock protecting local list of processes
    remote_spinlock_lock( XPTR( local_cxy , &cluster->pmgr.local_lock ) );

    // scan the local list of process descriptors to find the process
    xptr_t  iter;
    bool_t  found = false;
    XLIST_FOREACH( XPTR( local_cxy , &cluster->pmgr.local_root ) , iter )
    {
        process_xp  = XLIST_ELEMENT( iter , process_t , local_list );
        process_ptr = (process_t *)GET_PTR( process_xp );
        if( process_ptr->pid == pid )
        {
            found = true;
            break;
        }
    }

    // release lock protecting local list of processes
    remote_spinlock_unlock( XPTR( local_cxy , &cluster->pmgr.local_lock ) );

    // allocate memory for a new local process descriptor
    // and initialise it from reference cluster if required
    if( !found )
    {
        // get extended pointer on reference process descriptor
        xptr_t ref_xp = cluster_get_reference_process_from_pid( pid );

        assert( (ref_xp != XPTR_NULL) , __FUNCTION__ , "illegal pid\n" );

        // allocate memory for local process descriptor
        process_ptr = process_alloc();
        if( process_ptr == NULL )  return NULL;

        // initialize local process descriptor copy
        error = process_copy_init( process_ptr , ref_xp );
        if( error ) return NULL;
    }

    return process_ptr;
}

//////////////////////////////////////////////////////////////////////////////////////////
// File descriptor array related functions
//////////////////////////////////////////////////////////////////////////////////////////

///////////////////////////////////////////
void process_fd_init( process_t * process )
{
    uint32_t fd;

    remote_spinlock_init( XPTR( local_cxy , &process->fd_array.lock ) );

    process->fd_array.current = 0;

    // initialize array
    for ( fd = 0 ; fd < CONFIG_PROCESS_FILE_MAX_NR ; fd++ )
    {
        process->fd_array.array[fd] = XPTR_NULL;
    }
}

//////////////////////////////
bool_t process_fd_array_full()
{
    // get extended pointer on reference process
    xptr_t ref_xp = CURRENT_THREAD->process->ref_xp;

    // get reference process cluster and local pointer
    process_t * ref_ptr = (process_t *)GET_PTR( ref_xp );
    cxy_t       ref_cxy = GET_CXY( ref_xp );

    // get number of open file descriptors from reference fd_array
    uint32_t current = hal_remote_lw( XPTR( ref_cxy , &ref_ptr->fd_array.current ) );

        return ( current >= CONFIG_PROCESS_FILE_MAX_NR );
}

/////////////////////////////////////////////////
error_t process_fd_register( process_t * process,
                             xptr_t      file_xp,
                             uint32_t  * fdid )
{
    bool_t    found;
    uint32_t  id;
    xptr_t    xp;

    // get reference process cluster and local pointer
    xptr_t ref_xp = process->ref_xp;
    process_t * ref_ptr = (process_t *)GET_PTR( ref_xp );
    cxy_t       ref_cxy = GET_CXY( ref_xp );

    // take lock protecting reference fd_array
        remote_spinlock_lock( XPTR( ref_cxy , &ref_ptr->fd_array.lock ) );

    found   = false;

    for ( id = 0; id < CONFIG_PROCESS_FILE_MAX_NR ; id++ )
    {
        xp = hal_remote_lwd( XPTR( ref_cxy , &ref_ptr->fd_array.array[id] ) );
        if ( xp == XPTR_NULL )
        {
            found = true;
            hal_remote_swd( XPTR( ref_cxy , &ref_ptr->fd_array.array[id] ) , file_xp );
                hal_remote_atomic_add( XPTR( ref_cxy , &ref_ptr->fd_array.current ) , 1 );
                        *fdid = id;
            break;
        }
    }

    // release lock protecting reference fd_array
        remote_spinlock_unlock( XPTR( ref_cxy , &ref_ptr->fd_array.lock ) );

    if ( !found ) return EMFILE;
    else          return 0;
}

////////////////////////////////////////////////
xptr_t process_fd_get_xptr( process_t * process,
                            uint32_t    fdid )
{
    xptr_t  file_xp;

    // access local copy of process descriptor
    file_xp = process->fd_array.array[fdid];

    if( file_xp == XPTR_NULL )
    {
        // get reference process cluster and local pointer
        xptr_t      ref_xp  = process->ref_xp;
        cxy_t       ref_cxy = GET_CXY( ref_xp );
        process_t * ref_ptr = (process_t *)GET_PTR( ref_xp );

        // access reference process descriptor
        file_xp = hal_remote_lwd( XPTR( ref_cxy , &ref_ptr->fd_array.array[fdid] ) );

        // update local fd_array if found
        if( file_xp != XPTR_NULL )
        {
            process->fd_array.array[fdid] = file_xp;
        }
    }

    return file_xp;

}  // end process_fd_get_xptr()

///////////////////////////////////////////
void process_fd_remote_copy( xptr_t dst_xp,
                             xptr_t src_xp )
{
    uint32_t fd;
    xptr_t   entry;

    // get cluster and local pointer for src fd_array
    cxy_t        src_cxy = GET_CXY( src_xp );
    fd_array_t * src_ptr = (fd_array_t *)GET_PTR( src_xp );

    // get cluster and local pointer for dst fd_array
    cxy_t        dst_cxy = GET_CXY( dst_xp );
    fd_array_t * dst_ptr = (fd_array_t *)GET_PTR( dst_xp );

    // get the remote lock protecting the src fd_array
        remote_spinlock_lock( XPTR( src_cxy , &src_ptr->lock ) );

    // loop on all entries in source process fd_array
    for( fd = 0 ; fd < CONFIG_PROCESS_FILE_MAX_NR ; fd++ )
        {
                entry = (xptr_t)hal_remote_lwd( XPTR( src_cxy , &src_ptr->array[fd] ) );

                if( entry != XPTR_NULL )
                {
            // increment file descriptor ref count
            vfs_file_count_up( entry );

                        // copy entry in destination process fd_array
                        hal_remote_swd( XPTR( dst_cxy , &dst_ptr->array[fd] ) , entry );
                }
        }

    // release lock on source process fd_array
        remote_spinlock_unlock( XPTR( src_cxy , &src_ptr->lock ) );

}  // end process_fd_remote_copy()

////////////////////////////////////////////////////////////////////////////////////
//  Thread related functions
////////////////////////////////////////////////////////////////////////////////////

/////////////////////////////////////////////////////
error_t process_register_thread( process_t * process,
                                 thread_t  * thread,
                                 trdid_t   * trdid )
{
    ltid_t   ltid;
    bool_t   found;

    assert( (process != NULL) , __FUNCTION__ , "process argument is NULL" );

    assert( (thread != NULL) , __FUNCTION__ , "thread argument is NULL" );

    // search a free slot in th_tbl[] 
    // 0 is not a valid ltid value
    found = false;
    for( ltid = 1 ; ltid < CONFIG_THREAD_MAX_PER_CLUSTER ; ltid++ )
    {
        if( process->th_tbl[ltid] == NULL )
        {
            found = true;
            break;
        }
    }

    if( found )
    {
        // register thread in th_tbl[]
        process->th_tbl[ltid] = thread;
        process->th_nr++;

        // returns trdid
        *trdid = TRDID( local_cxy , ltid );
    }

    return (found) ? 0 : ENOMEM;

}  // end process_register_thread()

///////////////////////////////////////////////
void process_remove_thread( thread_t * thread )
{
    assert( (thread != NULL) , __FUNCTION__ , "thread argument is NULL" );

    process_t * process = thread->process;

    // get thread local index
    ltid_t  ltid = LTID_FROM_TRDID( thread->trdid );

    // remove thread from th_tbl[]
    process->th_tbl[ltid] = NULL;
    process->th_nr--;

}  // process_remove_thread()

/////////////////////////////////////////////////////
error_t process_make_exec( exec_info_t  * exec_info )
{
    char           * path;                            // pathname to .elf file
    bool_t           keep_pid;                        // new process keep parent PID if true
    process_t      * process;                         // local pointer on new process
    pid_t            pid;                             // new process pid
    xptr_t           parent_xp;                       // extended pointer on parent process
    cxy_t            parent_cxy;                      // parent process local cluster
    process_t      * parent_ptr;                      // local pointer on parent process
    uint32_t         parent_pid;                      // parent process identifier
    thread_t       * thread;                          // pointer on new thread
    pthread_attr_t   attr;                            // main thread attributes
    core_t         * core;                            // pointer on selected core
    lid_t            lid;                             // selected core local index
        error_t          error;

        // get .elf pathname, parent_xp, and keep_pid flag from exec_info
        path      = exec_info->path;
    parent_xp = exec_info->parent_xp;
    keep_pid  = exec_info->keep_pid;

process_dmsg("\n[DBG] %s : core[%x,%d] enters for path = %s\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, path );

    // get parent process cluster and local pointer
    parent_cxy = GET_CXY( parent_xp );
    parent_ptr = (process_t *)GET_PTR( parent_xp );
    parent_pid = hal_remote_lw( XPTR( parent_cxy , &parent_ptr->pid ) );

    // allocates memory for process descriptor 
        process = process_alloc(); 
        if( process == NULL ) return -1;

    // get PID
    if( keep_pid )    // keep parent PID
    {
        pid = parent_pid;
    }
    else              // get new PID from local cluster
    {
        error = cluster_pid_alloc( XPTR( local_cxy , process ) , &pid );
        if( error ) return -1;
    }

process_dmsg("\n[DBG] %s : core[%x,%d] created process %x for path = %s\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, pid, path );

    // initialize the process descriptor as the reference
    process_reference_init( process , pid , parent_xp );

process_dmsg("\n[DBG] %s : core[%x,%d] initialized process %x / path = %s\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, pid, path );

    // initialize vfs_root and vfs_cwd from parent process
    xptr_t  vfs_root_xp = hal_remote_lwd( XPTR( parent_cxy , &parent_ptr->vfs_root_xp ) );
        vfs_file_count_up( vfs_root_xp );
        process->vfs_root_xp = vfs_root_xp;

    xptr_t  vfs_cwd_xp = hal_remote_lwd( XPTR( parent_cxy , &parent_ptr->vfs_cwd_xp ) );
        vfs_file_count_up( vfs_cwd_xp );
        process->vfs_cwd_xp = vfs_cwd_xp;

    // initialize embedded fd_array from parent process
    process_fd_remote_copy( XPTR( local_cxy  , &process->fd_array ),
                            XPTR( parent_cxy , &parent_ptr->fd_array) );

process_dmsg("\n[DBG] %s :  core[%x,%d] copied fd_array for process %x\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, pid );

    // register "code" and "data" vsegs as well as the process entry-point in VMM,
    // using information contained in the elf file.
        error = elf_load_process( path , process );

        if( error )
        {
                printk("\n[ERROR] in %s : failed to access .elf file for process %x / path = %s\n",
                       __FUNCTION__, pid , path );
        process_destroy( process );
        return error;
        }

process_dmsg("\n[DBG] %s : core[%x,%d] registered code/data vsegs for process %x / path = %s\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, pid, path );

    // select a core in cluster
    lid  = cluster_select_local_core();
    core = &LOCAL_CLUSTER->core_tbl[lid];

    // initialize pthread attributes for main thread
    attr.attributes = PT_ATTR_DETACH | PT_ATTR_CLUSTER_DEFINED | PT_ATTR_CORE_DEFINED;
    attr.cxy        = local_cxy;
    attr.lid        = lid;

    // create and initialize thread descriptor
        error = thread_user_create( pid,
                                (void *)process->vmm.entry_point,
                                exec_info->args_pointers,
                                &attr,
                                &thread );
        if( error )
        {
                printk("\n[ERROR] in %s : cannot create thread for process %x / path = %s\n",
                       __FUNCTION__, pid , path );
        process_destroy( process );
        return error;
        }

process_dmsg("\n[DBG] %s : core[%x,%d] created thread %x for process %x / path = %s\n",
__FUNCTION__ , local_cxy, CURRENT_THREAD->core->lid, thread->trdid, pid, path  );

    // update children list in parent process
        xlist_add_last( XPTR( parent_cxy , &parent_ptr->children_root ),
                    XPTR( local_cxy  , &process->brothers_list ) );
        hal_remote_atomic_add( XPTR( parent_cxy , &parent_ptr->children_nr) , 1 );

    // activate new thread
        thread_unblock( XPTR( local_cxy , thread ) , THREAD_BLOCKED_GLOBAL );

process_dmsg("\n[DBG] %s : core[%x,%d] exit for path = %s\n",
__FUNCTION__, local_cxy, CURRENT_THREAD->core->lid, path  );

        return 0;

}  // end process_make_exec()

//////////////////////////
void process_init_create()
{
    exec_info_t   exec_info;     // structure to be passed to process_make_exec()
    xptr_t        parent_xp;     // extended pointer on parent process.
    error_t       error;

process_dmsg("\n[DBG] %s : enters in cluster %x\n", 
__FUNCTION__ , local_cxy );

    // parent process is local kernel process
    parent_xp = XPTR( local_cxy , &process_zero );

    // initialize the exec_info structure
    exec_info.keep_pid     = false;
    exec_info.parent_xp    = parent_xp;
    strcpy( exec_info.path , CONFIG_PROCESS_INIT_PATH );
    exec_info.args_nr      = 0;
    exec_info.envs_nr      = 0;

    // initialize process_init and create thread_init
        error = process_make_exec( &exec_info );

        if( error ) panic("cannot initialize process_init in cluster %x", local_cxy );

process_dmsg("\n[DBG] %s : exit in cluster %x\n", 
__FUNCTION__ , local_cxy );
                
    hal_fence();

}  // end process_init_create()