8c3c7314a8
git-svn-id: svn://svn.code.sf.net/p/nuttx/code/trunk@5520 42af7a65-404d-4744-a932-0658087f49c3
339 lines
11 KiB
C
339 lines
11 KiB
C
/****************************************************************************
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* sched/task_vfork
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*
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* Copyright (C) 2013 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <stdint.h>
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#include <assert.h>
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#include <queue.h>
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#include <errno.h>
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#include <debug.h>
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#include <nuttx/sched.h>
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#include "os_internal.h"
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#include "env_internal.h"
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/****************************************************************************
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* Pre-processor Definitions
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****************************************************************************/
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: task_vforksetup
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*
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* Description:
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* The vfork() function has the same effect as fork(), except that the
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* behavior is undefined if the process created by vfork() either modifies
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* any data other than a variable of type pid_t used to store the return
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* value from vfork(), or returns from the function in which vfork() was
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* called, or calls any other function before successfully calling _exit()
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* or one of the exec family of functions.
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*
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* This functin provides one step in the overall vfork() sequence: It
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* Allocates and initializes the child task's TCB. The overall sequence is:
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*
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* 1) User code calls vfork(). vfork() is provided in architecture-specific
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* code.
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* 2) vfork()and calls task_vforksetup().
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* 3) task_vforksetup() allocates and configures the child task's TCB. This
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* consists of:
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* - Allocation of the child task's TCB.
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* - Initialization of file descriptors and streams
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* - Configuration of environment variables
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* - Setup the intput parameters for the task.
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* - Initialization of the TCB (including call to up_initial_state()
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* 4) up_vfork() provides any additional operating context. up_vfork must:
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* - Allocate and initialize the stack
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* - Initialize special values in any CPU registers that were not
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* already configured by up_initial_state()
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* 5) up_vfork() then calls task_vforkstart()
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* 6) task_vforkstart() then executes the child thread.
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*
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* Input Paremeters:
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* retaddr - The return address from vfork() where the child task
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* will be started.
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*
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* Returned Value:
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* Upon successful completion, task_vforksetup() returns a pointer to
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* newly allocated and initalized child task's TCB. NULL is returned
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* on any failure and the errno is set appropriately.
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*
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****************************************************************************/
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FAR _TCB *task_vforksetup(start_t retaddr)
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{
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_TCB *parent = (FAR _TCB *)g_readytorun.head;
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_TCB *child;
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int priority;
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int ret;
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DEBUGASSERT(retaddr);
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/* Allocate a TCB for the child task. */
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child = (FAR _TCB*)kzalloc(sizeof(_TCB));
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if (!child)
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{
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set_errno(ENOMEM);
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return NULL;
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}
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/* Associate file descriptors with the new task */
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#if CONFIG_NFILE_DESCRIPTORS > 0 || CONFIG_NSOCKET_DESCRIPTORS > 0
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ret = sched_setuptaskfiles(child);
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if (ret != OK)
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{
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goto errout_with_tcb;
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}
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#endif
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/* Clone the parent's task environment */
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(void)env_dup(child);
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/* Mark the type of this thread (this setting will be needed in
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* task_schedsetup() when up_initial_state() is called.
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*/
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child->flags |= TCB_FLAG_TTYPE_TASK;
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/* Get the priority of the parent task */
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#ifdef CONFIG_PRIORITY_INHERITANCE
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priority = parent->base_priority; /* "Normal," unboosted priority */
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#else
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priority = parent->sched_priority; /* Current priority */
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#endif
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/* Initialize the task control block. This calls up_initial_state() */
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svdbg("Child priority=%d start=%p\n", priority, retaddr);
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ret = task_schedsetup(child, priority, retaddr, parent->entry.main);
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if (ret != OK)
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{
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goto errout_with_tcb;
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}
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svdbg("parent=%p, returning child=%p\n", parent, child);
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return child;
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errout_with_tcb:
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sched_releasetcb(child);
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set_errno(-ret);
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return NULL;
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}
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/****************************************************************************
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* Name: task_vforkstart
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*
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* Description:
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* The vfork() function has the same effect as fork(), except that the
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* behavior is undefined if the process created by vfork() either modifies
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* any data other than a variable of type pid_t used to store the return
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* value from vfork(), or returns from the function in which vfork() was
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* called, or calls any other function before successfully calling _exit()
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* or one of the exec family of functions.
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*
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* This functin provides one step in the overall vfork() sequence: It
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* starts execution of the previously initialized TCB. The overall
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* sequence is:
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*
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* 1) User code calls vfork()
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* 2) Architecture-specific code provides vfork()and calls task_vforksetup().
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* 3) task_vforksetup() allocates and configures the child task's TCB. This
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* consists of:
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* - Allocation of the child task's TCB.
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* - Initialization of file descriptors and streams
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* - Configuration of environment variables
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* - Setup the intput parameters for the task.
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* - Initialization of the TCB (including call to up_initial_state()
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* 4) vfork() provides any additional operating context. vfork must:
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* - Allocate and initialize the stack
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* - Initialize special values in any CPU registers that were not
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* already configured by up_initial_state()
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* 5) vfork() then calls task_vforkstart()
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* 6) task_vforkstart() then executes the child thread.
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*
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* Input Paremeters:
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* retaddr - The return address from vfork() where the child task
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* will be started.
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*
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* Returned Value:
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* Upon successful completion, vfork() returns 0 to the child process and
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* returns the process ID of the child process to the parent process.
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* Otherwise, -1 is returned to the parent, no child process is created,
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* and errno is set to indicate the error.
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*
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****************************************************************************/
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pid_t task_vforkstart(FAR _TCB *child)
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{
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#if CONFIG_TASK_NAME_SIZE > 0
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_TCB *parent = (FAR _TCB *)g_readytorun.head;
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#endif
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FAR const char *name;
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pid_t pid;
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#ifdef CONFIG_SCHED_WAITPID
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int rc;
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#endif
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int ret;
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svdbg("Starting Child TCB=%p, parent=%p\n", child, g_readytorun.head);
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DEBUGASSERT(child);
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/* Setup to pass parameters to the new task */
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#if CONFIG_TASK_NAME_SIZE > 0
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name = parent->name;
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#else
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name = NULL;
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#endif
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(void)task_argsetup(child, name, (const char **)NULL);
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/* Get the assigned pid before we start the task */
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pid = (int)child->pid;
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/* Activate the task */
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ret = task_activate(child);
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if (ret != OK)
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{
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task_vforkabort(child, -ret);
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return ERROR;
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}
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/* Since the child task has the same priority as the parent task, it is
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* now ready to run, but has not yet ran. It is a requirement that
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* the parent enivornment be stable while vfork runs; the child thread
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* is still dependent on things in the parent thread... like the pointers
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* into parent thread's stack which will still appear in the child's
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* registers and environment.
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*
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* We do not have SIG_CHILD, so we have to do some silly things here.
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* The simplest way to make sure that the child thread runs to completion
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* is simply to yield here. Since the child can only do exit() or
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* execv/l(), that should be all that is needed.
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*
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* Hmmm.. this is probably not sufficient. What if we are running
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* SCHED_RR? What if the child thread is suspeneded and rescheduled
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* after the parent thread again?
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*/
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#ifdef CONFIG_SCHED_WAITPID
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/* We can also exploit a bug in the execv() implementation: The PID
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* of the task exec'ed by the child will not be the same as the PID of
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* the child task. Therefore, waitpid() on the child task's PID will
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* accomplish what we need to do.
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*/
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rc = 0;
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#ifdef CONFIG_DEBUG
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ret = waitpid(pid, &rc, 0);
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if (ret < 0)
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{
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sdbg("ERROR: waitpid failed: %d\n", errno);
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}
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#else
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(void)waitpid(pid, &rc, 0);
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#endif
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#else
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/* The following logic does not appear to work... It gets stuff in an
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* infinite kill() loop and hogs the processor. Therefore, it looks
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* as though CONFIG_SCHED_WAITPID may be a requirement to used vfork().
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*
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* Again exploiting that execv() bug: Check if the child thread is
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* still running.
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*/
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while (kill(pid, 0) == OK)
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{
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/* Yes.. then we can yield to it -- assuming that it has not lowered
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* its priority. sleep(0) might be a safer thing to do since it does
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* not depend on prioirities: It will halt the parent thread for one
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* system clock tick. This will delay the return to the parent thread.
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*/
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#ifndef CONFIG_DISABLE_SIGNALS
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sleep(0);
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#else
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sched_yield();
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#endif
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}
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#endif
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return pid;
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}
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/****************************************************************************
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* Name: task_vforkabort
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*
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* Description:
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* Recover from any errors after task_vforksetup() was called.
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*
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* Returned Value:
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* None
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*
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****************************************************************************/
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void task_vforkabort(FAR _TCB *child, int errcode)
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{
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/* The TCB was added to the active task list by task_schedsetup() */
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dq_rem((FAR dq_entry_t*)child, (dq_queue_t*)&g_inactivetasks);
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/* Release the TCB */
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sched_releasetcb(child);
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set_errno(errcode);
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}
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