/****************************************************************************
* sched/task_vfork
*
* Copyright (C) 2013 Gregory Nutt. All rights reserved.
* Author: Gregory Nutt <gnutt@nuttx.org>
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
* 3. Neither the name NuttX nor the names of its contributors may be
* used to endorse or promote products derived from this software
* without specific prior written permission.
*
* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
* POSSIBILITY OF SUCH DAMAGE.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/wait.h>
#include <stdint.h>
#include <assert.h>
#include <queue.h>
#include <errno.h>
#include <debug.h>
#include <nuttx/sched.h>
#include "os_internal.h"
#include "group_internal.h"
/****************************************************************************
* Pre-processor Definitions
****************************************************************************/
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: task_vforksetup
*
* Description:
* The vfork() function has the same effect as fork(), except that the
* behavior is undefined if the process created by vfork() either modifies
* any data other than a variable of type pid_t used to store the return
* value from vfork(), or returns from the function in which vfork() was
* called, or calls any other function before successfully calling _exit()
* or one of the exec family of functions.
*
* This functin provides one step in the overall vfork() sequence: It
* Allocates and initializes the child task's TCB. The overall sequence is:
*
* 1) User code calls vfork(). vfork() is provided in architecture-specific
* code.
* 2) vfork()and calls task_vforksetup().
* 3) task_vforksetup() allocates and configures the child task's TCB. This
* consists of:
* - Allocation of the child task's TCB.
* - Initialization of file descriptors and streams
* - Configuration of environment variables
* - Setup the intput parameters for the task.
* - Initialization of the TCB (including call to up_initial_state()
* 4) up_vfork() provides any additional operating context. up_vfork must:
* - Allocate and initialize the stack
* - Initialize special values in any CPU registers that were not
* already configured by up_initial_state()
* 5) up_vfork() then calls task_vforkstart()
* 6) task_vforkstart() then executes the child thread.
*
* Input Paremeters:
* retaddr - The return address from vfork() where the child task
* will be started.
*
* Returned Value:
* Upon successful completion, task_vforksetup() returns a pointer to
* newly allocated and initalized child task's TCB. NULL is returned
* on any failure and the errno is set appropriately.
*
****************************************************************************/
FAR struct tcb_s *task_vforksetup(start_t retaddr)
{
struct tcb_s *parent = (FAR struct tcb_s *)g_readytorun.head;
struct task_tcb_s *child;
int priority;
int ret;
DEBUGASSERT(retaddr);
/* Allocate a TCB for the child task. */
child = (FAR struct task_tcb_s *)kzalloc(sizeof(struct task_tcb_s));
if (!child)
{
set_errno(ENOMEM);
return NULL;
}
/* Associate file descriptors with the new task */
#if CONFIG_NFILE_DESCRIPTORS > 0 || CONFIG_NSOCKET_DESCRIPTORS > 0
ret = group_setuptaskfiles(child);
if (ret != OK)
{
goto errout_with_tcb;
}
#endif
/* Get the priority of the parent task */
#ifdef CONFIG_PRIORITY_INHERITANCE
priority = parent->base_priority; /* "Normal," unboosted priority */
#else
priority = parent->sched_priority; /* Current priority */
#endif
/* Initialize the task control block. This calls up_initial_state() */
svdbg("Child priority=%d start=%p\n", priority, retaddr);
ret = task_schedsetup(child, priority, retaddr, parent->entry.main,
TCB_FLAG_TTYPE_TASK);
if (ret != OK)
{
goto errout_with_tcb;
}
svdbg("parent=%p, returning child=%p\n", parent, child);
return (FAR struct tcb_s *)child;
errout_with_tcb:
sched_releasetcb((FAR struct tcb_s *)child);
set_errno(-ret);
return NULL;
}
/****************************************************************************
* Name: task_vforkstart
*
* Description:
* The vfork() function has the same effect as fork(), except that the
* behavior is undefined if the process created by vfork() either modifies
* any data other than a variable of type pid_t used to store the return
* value from vfork(), or returns from the function in which vfork() was
* called, or calls any other function before successfully calling _exit()
* or one of the exec family of functions.
*
* This functin provides one step in the overall vfork() sequence: It
* starts execution of the previously initialized TCB. The overall
* sequence is:
*
* 1) User code calls vfork()
* 2) Architecture-specific code provides vfork()and calls task_vforksetup().
* 3) task_vforksetup() allocates and configures the child task's TCB. This
* consists of:
* - Allocation of the child task's TCB.
* - Initialization of file descriptors and streams
* - Configuration of environment variables
* - Setup the intput parameters for the task.
* - Initialization of the TCB (including call to up_initial_state()
* 4) vfork() provides any additional operating context. vfork must:
* - Allocate and initialize the stack
* - Initialize special values in any CPU registers that were not
* already configured by up_initial_state()
* 5) vfork() then calls task_vforkstart()
* 6) task_vforkstart() then executes the child thread.
*
* Input Paremeters:
* retaddr - The return address from vfork() where the child task
* will be started.
*
* Returned Value:
* Upon successful completion, vfork() returns 0 to the child process and
* returns the process ID of the child process to the parent process.
* Otherwise, -1 is returned to the parent, no child process is created,
* and errno is set to indicate the error.
*
****************************************************************************/
pid_t task_vforkstart(FAR struct tcb_s *child)
{
#if CONFIG_TASK_NAME_SIZE > 0
struct tcb_s *parent = (FAR struct tcb_s *)g_readytorun.head;
#endif
FAR const char *name;
pid_t pid;
#ifdef CONFIG_SCHED_WAITPID
int rc;
#endif
int ret;
svdbg("Starting Child TCB=%p, parent=%p\n", child, g_readytorun.head);
DEBUGASSERT(child);
/* Setup to pass parameters to the new task */
#if CONFIG_TASK_NAME_SIZE > 0
name = parent->name;
#else
name = NULL;
#endif
(void)task_argsetup(child, name, (const char **)NULL);
/* Get the assigned pid before we start the task */
pid = (int)child->pid;
/* Activate the task */
ret = task_activate(child);
if (ret != OK)
{
task_vforkabort(child, -ret);
return ERROR;
}
/* Since the child task has the same priority as the parent task, it is
* now ready to run, but has not yet ran. It is a requirement that
* the parent enivornment be stable while vfork runs; the child thread
* is still dependent on things in the parent thread... like the pointers
* into parent thread's stack which will still appear in the child's
* registers and environment.
*
* We do not have SIG_CHILD, so we have to do some silly things here.
* The simplest way to make sure that the child thread runs to completion
* is simply to yield here. Since the child can only do exit() or
* execv/l(), that should be all that is needed.
*
* Hmmm.. this is probably not sufficient. What if we are running
* SCHED_RR? What if the child thread is suspeneded and rescheduled
* after the parent thread again?
*/
#ifdef CONFIG_SCHED_WAITPID
/* We can also exploit a bug in the execv() implementation: The PID
* of the task exec'ed by the child will not be the same as the PID of
* the child task. Therefore, waitpid() on the child task's PID will
* accomplish what we need to do.
*/
rc = 0;
#ifdef CONFIG_DEBUG
ret = waitpid(pid, &rc, 0);
if (ret < 0)
{
sdbg("ERROR: waitpid failed: %d\n", errno);
}
#else
(void)waitpid(pid, &rc, 0);
#endif
#else
/* The following logic does not appear to work... It gets stuff in an
* infinite kill() loop and hogs the processor. Therefore, it looks
* as though CONFIG_SCHED_WAITPID may be a requirement to used vfork().
*
* Again exploiting that execv() bug: Check if the child thread is
* still running.
*/
while (kill(pid, 0) == OK)
{
/* Yes.. then we can yield to it -- assuming that it has not lowered
* its priority. sleep(0) might be a safer thing to do since it does
* not depend on prioirities: It will halt the parent thread for one
* system clock tick. This will delay the return to the parent thread.
*/
#ifndef CONFIG_DISABLE_SIGNALS
sleep(0);
#else
sched_yield();
#endif
}
#endif
return pid;
}
/****************************************************************************
* Name: task_vforkabort
*
* Description:
* Recover from any errors after task_vforksetup() was called.
*
* Returned Value:
* None
*
****************************************************************************/
void task_vforkabort(FAR struct tcb_s *child, int errcode)
{
/* The TCB was added to the active task list by task_schedsetup() */
dq_rem((FAR dq_entry_t*)child, (dq_queue_t*)&g_inactivetasks);
/* Release the TCB */
sched_releasetcb(child);
set_errno(errcode);
}
