/*
 * sys_fork.c - Fork the current process.
 * 
 * Authors  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_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>

//////////////
int sys_fork()
{
	process_t          * parent_process;  // pointer on parent process descriptor
    pid_t                parent_pid;      // parent process identifier
    thread_t           * parent_thread;   // pointer on parent thread descriptor
	process_t          * child_process;   // pointer on child process descriptor
    pid_t                child_pid;       // child process identifier
	thread_t           * child_thread;    // pointer on child main thread descriptor
    cxy_t                target_cxy;      // target cluster for forked child process 
	error_t              error;

	uint64_t      tm_start;
	uint64_t      tm_end;

	tm_start = hal_get_cycles();

    // get pointers on parent process and thread
	parent_thread  = CURRENT_THREAD;
	parent_process = parent_thread->process;
    parent_pid     = parent_process->pid;

fork_dmsg("\n[DBG] %s : core[%x,%d] enters for process %x / cycle %d\n",
__FUNCTION__ , local_cxy , parent_thread->core->lid , parent_pid , (uint32_t)tm_start );

    // check parent process children number
	if( hal_atomic_add( &parent_process->children_nr , 1 ) >= CONFIG_PROCESS_MAX_CHILDREN )
	{
	    printk("\n[ERROR] in %s : too much children processes\n", __FUNCTION__);
	    hal_atomic_add ( &parent_process->children_nr , -1 );
        return EAGAIN;
	}

    // Select target cluster for future migration of child process and main thread.
    // If placement is not user-defined, the placement is defined by the DQDT. 
    // The two first processes ("init" and "sh") on boot cluster do not migrate. 

	if( parent_thread->fork_user )
	{
        // user defined placement
        target_cxy = parent_thread->fork_cxy;
        parent_thread->fork_user = false;
	}
    else if( (LPID_FROM_PID(parent_process->pid) < 2)  && (local_cxy == 0) )
    {
        // 2 first process stay in boot cluster
        target_cxy = local_cxy;
    }
	else
	{
        // DQDT placement
		target_cxy = dqdt_get_cluster_for_process();
	}

//printk("\n[DBG] %s : core[%x,%d] for process %x selects target_cluster = %x\n",
//__FUNCTION__ , local_cxy , parent_thread->core->lid , parent_pid , target_cxy );

    // allocates memory in local cluster for the child process descriptor 
	child_process = process_alloc(); 

	if( child_process == NULL )
	{
	    printk("\n[ERROR] in %s : cannot allocate child process\n", __FUNCTION__ );
	    hal_atomic_add ( &parent_process->children_nr , -1 );
        return EAGAIN;
	}

    // get a new PID for child process,
    if( target_cxy == local_cxy )                // target cluster is local
    {
        error = cluster_pid_alloc( XPTR( target_cxy , child_process ) , &child_pid );
    }
    else                                         // target cluster is remote
    {
        rpc_process_pid_alloc_client( target_cxy , child_process , &error , &child_pid );
    }

    if( error )
    {
	    printk("\n[ERROR] in %s : cannot allocate PID\n", __FUNCTION__ );
	    hal_atomic_add ( &parent_process->children_nr , -1 );
        process_destroy( child_process );
        return EAGAIN;
    }

    // initialize and register the child process descriptor
    process_reference_init( child_process , child_pid , XPTR(local_cxy, parent_process) );

    // initialises child process standard files structures
    // ( root / cwd / bin ) from parent process descriptor

	vfs_file_count_up( parent_process->vfs_root_xp );
	child_process->vfs_root_xp = parent_process->vfs_root_xp;

	vfs_file_count_up( parent_process->vfs_cwd_xp );
	child_process->vfs_cwd_xp  = parent_process->vfs_cwd_xp;

	vfs_file_count_up( parent_process->vfs_bin_xp );
    child_process->vfs_bin_xp = parent_process->vfs_bin_xp;

    // copy the parent process fd_array to the child process fd_array
	process_fd_remote_copy( XPTR( local_cxy , &child_process->fd_array ),
                            XPTR( local_cxy , &parent_process->fd_array ) );

//printk("\n[DBG] %s : core[%x,%d] for process %x created child process %x\n",
//__FUNCTION__ , local_cxy , parent_thread->core->lid , parent_pid , child_pid );

    // replicate VMM
	error = vmm_copy( child_process , parent_process );

	if( error )
    {
	    printk("\n[ERROR] in %s : cannot duplicate VMM\n", __FUNCTION__ );
	    hal_atomic_add ( &parent_process->children_nr , -1 );
        process_destroy( child_process );
        return ENOMEM;
    }
  
//printk("\n[DBG] %s : core[%x,%d] for process %x duplicated vmm in child process\n",
//__FUNCTION__ , local_cxy , parent_thread->core->lid , parent_pid );
//vmm_display( parent_process , true );
//vmm_display( child_process , true );

    // create child main thread in local cluster 
    error = thread_user_fork( child_process,
                              parent_thread->u_stack_size,
                              parent_thread->u_stack_base,
                              &child_thread );
	if( error )
    {
	    printk("\n[ERROR] in %s : cannot duplicate main thread\n", __FUNCTION__ );
	    hal_atomic_add( &parent_process->children_nr , -1 );
        process_destroy( child_process );
        return ENOMEM;
    }

//printk("\n[DBG] %s : core[%x,%d] initialised child main thread\n",
//__FUNCTION__ , local_cxy , parent_thread->core->lid );

	// update DQDT for the child thread 
    dqdt_local_update_threads( 1 );

    // set child_thread FPU_context from parent_thread register values
    // only when the parent process is the FPU owner
	if( CURRENT_THREAD->core->fpu_owner == parent_thread )
	{
		hal_fpu_context_save( child_thread->fpu_context );
	}

    // set child_thread CPU context from parent_thread register values
    hal_do_cpu_save( child_thread->cpu_context,
                     child_thread,
                     (int)((intptr_t)child_thread - (intptr_t)parent_thread) );


    // from this point, both parent and child threads execute the following code
    // but child execute it only when it has been unblocked by its parent

    thread_t * current = CURRENT_THREAD;

    if( current == parent_thread )
    {
        // parent_thread unblock child_thread
        thread_unblock( XPTR( local_cxy , child_thread ) , THREAD_BLOCKED_GLOBAL );

        tm_end = hal_get_cycles();

fork_dmsg("\n[DBG] %s : core[%x,%d] parent_process %x exit / cycle %d\n"
"     child_process %x / child_thread = %x / cost = %d\n",
__FUNCTION__, local_cxy, parent_thread->core->lid,  parent_pid, (uint32_t)tm_start,
child_pid, child_thread->trdid , (uint32_t)(tm_end - tm_start) );

        return child_pid;
    }
	else  // current == child_thread
    {
        assert( (current == child_thread) , __FUNCTION__ , 
        "current thread %x is not the child thread %x\n", current , child_thread );

fork_dmsg("\n[DBG] %s : core[%x,%d] child process %x exit / cycle %d\n",
__FUNCTION__, local_cxy, parent_thread->core->lid, child_pid, (uint32_t)hal_get_cycles() );

        return 0;
    }

}  // end sys_fork()