source: trunk/kernel/syscalls/sys_fork.c

/*
 * sys_fork.c - Kernel function implementing the "fork" system call.
 * 
 * Authors  Alain Greiner  (2016,2017,2018,2019,2020)
 *
 * 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_kernel_types.h>
#include <hal_context.h>
#include <hal_switch.h>
#include <hal_atomic.h>
#include <errno.h>
#include <printk.h>
#include <core.h>
#include <cluster.h>
#include <list.h>
#include <thread.h>
#include <scheduler.h>
#include <kmem.h>
#include <dqdt.h>
#include <process.h>

#include <syscalls.h>

////////////////////
int sys_fork( void )
{
        process_t       * parent_process_ptr;   // pointer on local parent process descriptor
    xptr_t            parent_thread_xp;     // extended pointer on parent thread descriptor
    pid_t             parent_pid;           // parent process identifier
    thread_t        * parent_thread_ptr;    // local pointer on local parent thread
    cxy_t             parent_cxy;           // parent thread cluster

    pid_t             child_pid;            // child process identifier
    thread_t        * child_thread_ptr;     // local pointer on remote child thread 
    cxy_t             child_cxy;            // target cluster for forked child process 
 
    xptr_t            ref_process_xp;       // extended pointer on reference parent process
    cxy_t             ref_process_cxy;      // cluster of reference parent process
    process_t       * ref_process_ptr;      // local pointer on reference parent process

        error_t           error;

    // get pointers on local parent process and thread
        parent_thread_ptr  = CURRENT_THREAD;
    parent_thread_xp   = XPTR( local_cxy , parent_thread_ptr );
        parent_process_ptr = parent_thread_ptr->process;
    parent_pid         = parent_process_ptr->pid;
    parent_cxy         = local_cxy;

#if DEBUG_SYS_FORK || DEBUG_SYSCALLS_ERROR || CONFIG_INSTRUMENTATION_SYSCALLS
uint64_t     tm_start = hal_get_cycles();
#endif

#if DEBUG_SYS_FORK
if( DEBUG_SYS_FORK < (uint32_t)tm_start )
printk("\n[%s] thread[%x,%x] enter / cycle =  %d\n",
__FUNCTION__, parent_pid, parent_thread_ptr->trdid, (uint32_t)tm_start );
#endif

    // get infos on reference parent process
    ref_process_xp  = parent_process_ptr->ref_xp;
    ref_process_cxy = GET_CXY( ref_process_xp );
    ref_process_ptr = GET_PTR( ref_process_xp );

    // check parent process children number from reference
    xptr_t   children_xp = XPTR( ref_process_cxy , &ref_process_ptr->children_nr );
    if( hal_remote_atomic_add( children_xp , 1 ) >= CONFIG_PROCESS_MAX_CHILDREN )
        {

#if DEBUG_SYSCALLS_ERROR
if( DEBUG_SYSCALLS_ERROR < (uint32_t)tm_start )
printk("\n[ERROR] in %s : thread[%x,%x] / too much children\n",
__FUNCTION__, parent_pid, parent_thread_ptr->trdid );
#endif
            hal_remote_atomic_add ( children_xp , -1 );
        parent_thread_ptr->errno = EAGAIN;
        return -1;
        }

    // Select target cluster for child process and main thread.
    // If placement is not user-defined, it is defined by the DQDT. 
        if( parent_thread_ptr->fork_user )
        {
        child_cxy = parent_thread_ptr->fork_cxy;
        parent_thread_ptr->fork_user = false;
        }
        else                                  // DQDT placement
        {
                child_cxy = dqdt_get_cluster_for_thread( LOCAL_CLUSTER->dqdt_root_xp );
        }

#if (DEBUG_SYS_FORK & 1 )
if( DEBUG_SYS_FORK < (uint32_t)tm_start )
printk("\n[%s] thread[%x,%x] selected cluster %x\n",
__FUNCTION__, parent_pid, parent_thread_ptr->trdid, child_cxy );
#endif

    // call process_make_fork in target cluster
    if( child_cxy == local_cxy )
    {
        error = process_make_fork( ref_process_xp,
                                   parent_thread_xp,
                                   &child_pid,
                                   &child_thread_ptr );
    }
    else
    {
        rpc_process_make_fork_client( child_cxy,
                                      ref_process_xp,
                                      parent_thread_xp,
                                      &child_pid,
                                      &child_thread_ptr,
                                      &error );
    }

    if( error )
    {

#if DEBUG_SYSCALLS_ERROR
if( DEBUG_SYSCALLS_ERROR < (uint32_t)tm_start )
printk("\n[ERROR] in %s : thread[%x,%x] cannot fork\n",
__FUNCTION__, parent_pid, parent_thread_ptr->trdid );
#endif
        parent_thread_ptr->errno = EAGAIN;
        return -1;
    }

    // set remote child FPU_context from parent_thread register values
    // only when the parent thread is the FPU owner
        if( CURRENT_THREAD->core->fpu_owner == parent_thread_ptr )
        {
                hal_fpu_context_save( XPTR( child_cxy , child_thread_ptr ) );
        }

    // set the remote child CPU context from parent register values,
    // set the remote child uzone from 
    // replicates the parent thread kernel stack to the child thread descriptor,
    // and finally unblock the child thread. 
    hal_cpu_context_fork( XPTR( child_cxy , child_thread_ptr ) );

    // From this point, both parent and child threads execute the following code,
    // but child thread will only execute it after being unblocked by parent thread.
    // They can be distinguished by the (CURRENT_THREAD,local_cxy) values.
    // - parent return child PID to user application.
    // - child  return 0 to user application 

    thread_t * current = CURRENT_THREAD;

#if (DEBUG_SYS_FORK || CONFIG_INSTRUMENTATION_SYSCALLS)
uint64_t     tm_end = hal_get_cycles();
#endif

    if( (current == parent_thread_ptr) && (local_cxy == parent_cxy) )   // parent thread
    {

#if DEBUG_SYS_FORK
if( DEBUG_SYS_FORK < (uint32_t)tm_end )
printk("\n[%s] parent thread[%x,%x] exit / child_pid %x / cycle %d\n",
__FUNCTION__, current->process->pid, current->trdid, child_pid, (uint32_t)tm_end );
#endif

// only parent display the parent and child VMM
#if (DEBUG_SYS_FORK & 1 )
if( DEBUG_SYS_FORK < (uint32_t)tm_end )
{
    process_t * child_process_ptr = hal_remote_lpt( XPTR( child_cxy , 
                                                          &child_thread_ptr->process ) );
    xptr_t      child_process_xp  = XPTR( child_cxy , child_process_ptr );

    hal_vmm_display( ref_process_xp , true ); 
    hal_vmm_display( child_process_xp , true );
}
#endif

// only parent contribute to syscalls instrumentation
#if CONFIG_INSTRUMENTATION_SYSCALLS
hal_atomic_add( &syscalls_cumul_cost[SYS_FORK] , tm_end - tm_start );
hal_atomic_add( &syscalls_occurences[SYS_FORK] , 1 );
#endif
        return child_pid;
    }
        else                                                               // child_thread
    {

#if DEBUG_SYS_FORK
if( DEBUG_SYS_FORK < (uint32_t)tm_end )
printk("\n[%s] child thread[%x,%x] exit / child_pid %x / cycle %d\n",
__FUNCTION__, current->process->pid, current->trdid, child_pid, (uint32_t)tm_end );
#endif

        return 0;
    }

}  // end sys_fork()