Support task_wait / task_wait_tid syscalls:

    - Add task_end2 syscall to allow pthread_exit-like retval.
    - Add/maintain task states.
    - Create task parent/child tracking tree.
    - Add task_detach function.
    - Implement wait syscalls.

Make task_exec caller the parent of spawned task:

    Previously the task_exec call caused a message to the
    VFS task, which called task_create and returned the tid
    in response to the message.  This causes the parent of
    the spawned task to appear to be the VFS task.

    Modify task_exec / VFS handling to instead return the
    entry point address on the message and have task_exec call
    task_create directly itself.

Change-Id: I6b6796f45875de37b1ab01e7596639b073820b95
Reviewed-on: http://gfw160.austin.ibm.com:8080/gerrit/443
Tested-by: Jenkins Server
Reviewed-by: Daniel M. Crowell <dcrowell@us.ibm.com>
Reviewed-by: Andrew J. Geissler <andrewg@us.ibm.com>

3 files changed, 106 insertions, 6 deletions

diff --git a/src/include/sys/syscall.h b/src/include/sys/syscall.h
index f0972e949..b3d435edf 100644
--- a/src/include/sys/syscall.h
+++ b/src/include/sys/syscall.h
@@ -23,13 +23,21 @@
 #ifndef __SYS_SYSCALL_H
 #define __SYS_SYSCALL_H
 
+/** @file syscall.h
+ *  @brief Defines syscall wrapper functions to get C-caller to put syscall
+ *         parameters in the correct spots for ABI so kernel can pull them
+ *         from the right position in the task structs.
+ */
+
 #ifdef __cplusplus
-extern "C" 
+extern "C"
 {
 #endif
 
 #include <stdint.h>
+#include <builtins.h>
 
+// Normal system calls.
 void* _syscall0(uint64_t);
 void* _syscall1(uint64_t, void*);
 void* _syscall2(uint64_t, void*, void*);
@@ -39,6 +47,19 @@ void* _syscall5(uint64_t, void*, void*, void*, void*, void*);
 void* _syscall6(uint64_t, void*, void*, void*, void*, void*, void*);
 void* _syscall7(uint64_t, void*, void*, void*, void*, void*, void*, void*);
 
+// System calls which never return.  Marked NO_RETURN so the compiler
+// can make additional optimizations.
+void* _syscall0_nr(uint64_t) NO_RETURN;
+void* _syscall1_nr(uint64_t, void*) NO_RETURN;
+void* _syscall2_nr(uint64_t, void*, void*) NO_RETURN;
+void* _syscall3_nr(uint64_t, void*, void*, void*) NO_RETURN;
+void* _syscall4_nr(uint64_t, void*, void*, void*, void*) NO_RETURN;
+void* _syscall5_nr(uint64_t, void*, void*, void*, void*, void*) NO_RETURN;
+void* _syscall6_nr(uint64_t, void*, void*, void*, void*, void*, void*)
+            NO_RETURN;
+void* _syscall7_nr(uint64_t, void*, void*, void*, void*, void*, void*, void*)
+            NO_RETURN;
+
 #ifdef __cplusplus
 }
 #include <kernel/syscalls.H>
diff --git a/src/include/sys/task.h b/src/include/sys/task.h
index 9f43996c4..0627784f1 100644
--- a/src/include/sys/task.h
+++ b/src/include/sys/task.h
@@ -27,6 +27,7 @@
 #define __SYS_TASK_H
 
 #include <stdint.h>
+#include <builtins.h>
 #include <kernel/types.h>
 
 #ifdef __cplusplus
@@ -64,7 +65,17 @@ tid_t task_create(void(*start_routine)(void*), void* arg);
  *        function.  Therefore, returning from the entry point function will
  *        also cause the task to end cleanly using this function.
  */
-void task_end();
+void task_end() NO_RETURN;
+
+/** @fn task_end2
+ *  @brief End the calling task with a return value.
+ *
+ *  See POSIX pthread_exit.
+ *
+ *  @param[in] retval - A pointer to return to the task performing task_join /
+ *                      task_wait on this task.
+ */
+void task_end2(void* retval) NO_RETURN;
 
 /** @fn task_gettid
  *  @brief Get task ID of calling task.
@@ -130,6 +141,75 @@ void task_affinity_unpin();
  */
 void task_affinity_migrate_to_master();
 
+/** @enum task_status
+ *  @brief Status of how a task exited.
+ */
+enum task_status
+{
+        /** Task called task_end cleanly. */
+    TASK_STATUS_EXITED_CLEAN,
+        /** Task crashed.  Ended by the kernel due to error. */
+    TASK_STATUS_CRASHED,
+};
+
+/** @fn task_detach
+ *  @brief Sets the calling task to the 'detached' state, meaning no parent
+ *         may task_wait_tid on it.
+ */
+void task_detach();
+
+/** @fn task_wait_tid
+ *  @brief Block calling task until a requested child process exits.
+ *
+ *  See also: POSIX 'waitid' / Linux 'waitpid'.
+ *
+ *  @param[in] tid - Task to wait for completion.
+ *
+ *  @param[out] status - Optional address to write child status.
+ *  @param[out] retval - Optional address to write return-value.
+ *
+ *  Status values come from task_status enumeration.
+ *  Retval values come from child's 'task_end2' parameter.
+ *
+ *  @note All non-detached tasks must be waited on by their parent to ensure
+ *        there are not kernel memory-leaks.
+ *
+ *  @note If a parent task ends prior to waiting on its children, the children
+ *        become parented by their grand-parents, who must do the wait.
+ *
+ *  @return tid of child waited on or negative number on error.
+ *
+ *  @retval EDEADLK - Performing this wait would deadlock the caller such as
+ *                    when it has no children.
+ *  @retval EFAULT - Bad memory address given for status or retval parameter.
+ */
+tid_t task_wait_tid(tid_t tid, int* status, void** retval);
+
+/** @fn task_wait
+ *  @brief Block calling task until any child process exits.
+ *
+ *  See also: Linux 'wait'.
+ *
+ *  @param[out] status - Optional address to write child status.
+ *  @param[out] retval - Optional address to write return-value.
+ *
+ *  Status values come from task_status enumeration.
+ *  Retval values come from child's 'task_end2' parameter.
+ *
+ *  @note All non-detached tasks must be waited on by their parent to ensure
+ *        there are not kernel memory-leaks.
+ *
+ *  @note If a parent task ends prior to waiting on its children, the children
+ *        become parented by their grand-parents, who must do the wait.
+ *
+ *  @return tid of child waited on or negative number on error.
+ *
+ *  @retval EDEADLK - Performing this wait would deadlock the caller such as
+ *                    when it has no children.
+ *  @retval EFAULT - Bad memory address given for status or retval parameter.
+ */
+tid_t task_wait(int* status, void** retval);
+
 #ifdef __cplusplus
 }
 #endif
diff --git a/src/include/sys/vfs.h b/src/include/sys/vfs.h
index 6ab24c9b8..d427c0abb 100644
--- a/src/include/sys/vfs.h
+++ b/src/include/sys/vfs.h
@@ -102,14 +102,13 @@ extern uint64_t VFS_LAST_ADDRESS;
 VfsSystemModule * vfs_find_module(VfsSystemModule * i_table, const char * i_name);
 
 /**
- * Call the module start routine
+ * Get the module's start routine
  * @param[in] i_module VfsSystemModule data for the module
- * @param[in] i_param parameter to pass to task_create() for this module
- * @return tid_t of started task or negative value on error.
+ * @return Function pointer of module's start or negative value on error.
  * @retval -ENOENT if i_module is NULL
  * @retval -ENOEXEC if there is no start()
  */
-tid_t vfs_exec(VfsSystemModule * i_module, void* i_param);
+void* vfs_start_entrypoint(VfsSystemModule * i_module);
 
 /**
  * Change permissions on the virtual pages associated with the module