[PATCH] (update) Process Aggregates (PAGG) for 2.6.7

[Erik Jacobson]

Attached is the PAGG patch for kernel 2.6.7.  Some may recall I posted an
earlier PAGG patch for 2.6.7.  This version has improved handling for
the init function pointer functionality introduced earlier.

We'd be very interested in seeing this be accepted in to the kernel.  If
there is anything we should adjust to make it more likely to be accepted,
please reply.  Thanks.

Signed-off-by: Erik Jacobson <erikj@xxxxxxx>

--
Erik Jacobson - Linux System Software - Silicon Graphics - Eagan, MinnesotaIndex: linux/Documentation/pagg.txt
===================================================================
--- /dev/null
+++ linux/Documentation/pagg.txt
@@ -0,0 +1,32 @@
+Linux Process Aggregates (PAGG)
+-------------------------------
+
+The process aggregates infrastructure, or PAGG, provides a generalized
+mechanism for providing arbitrary process groups in Linux.  PAGG consists
+of a series of functions for registering and unregistering support
+for new types of process aggregation containers with the kernel.
+This is similar to the support currently provided within Linux that
+allows for dynamic support of filesystems, block and character devices,
+symbol tables, network devices, serial devices, and execution domains.
+This implementation of PAGG provides developers the basic hooks necessary
+to implement kernel modules for specific process containers, such as
+the job container.
+
+The do_fork function in the kernel was altered to support PAGG.  If a
+process is attached to any PAGG containers and subsequently forks a
+child process, the child process will also be attached to the same PAGG
+containers.  The PAGG containers involved during the fork are notified
+that a new process has been attached.  The notification is accomplished
+via a callback function provided by the PAGG module.
+
+The do_exit function in the kernel has also been altered.  If a process
+is attached to any PAGG containers and that process is exiting, the PAGG
+containers are notified that a process has detached from the container.
+The notification is accomplished via a callback function provided by
+the PAGG module.
+
+The sys_execve function has been modified to support an optional callout
+that can be run when a process in a pagg list does an exec.  It can be 
+used, for example, by other kernel modules that wish to do advanced CPU
+placement on multi-processor systems (just one example).
+
Index: linux/fs/exec.c
===================================================================
--- linux.orig/fs/exec.c
+++ linux/fs/exec.c
@@ -46,6 +46,7 @@
 #include <linux/security.h>
 #include <linux/syscalls.h>
 #include <linux/rmap.h>
+#include <linux/pagg.h>
 
 #include <asm/uaccess.h>
 #include <asm/pgalloc.h>
@@ -1133,6 +1134,7 @@
 	retval = search_binary_handler(&bprm,regs);
 	if (retval >= 0) {
 		free_arg_pages(&bprm);
+		pagg_exec(current);
 
 		/* execve success */
 		security_bprm_free(&bprm);
Index: linux/include/linux/init_task.h
===================================================================
--- linux.orig/include/linux/init_task.h
+++ linux/include/linux/init_task.h
@@ -2,6 +2,7 @@
 #define _LINUX__INIT_TASK_H
 
 #include <linux/file.h>
+#include <linux/pagg.h>
 
 #define INIT_FILES \
 { 							\
@@ -112,6 +113,7 @@
 	.proc_lock	= SPIN_LOCK_UNLOCKED,				\
 	.switch_lock	= SPIN_LOCK_UNLOCKED,				\
 	.journal_info	= NULL,						\
+	INIT_TASK_PAGG(tsk)						\
 }
 
 
Index: linux/include/linux/pagg.h
===================================================================
--- /dev/null
+++ linux/include/linux/pagg.h
@@ -0,0 +1,202 @@
+/* 
+ * PAGG (Process Aggregates) interface
+ *
+ * 
+ * Copyright (c) 2000-2002, 2004 Silicon Graphics, Inc.  All Rights Reserved.
+ *
+ * This program 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ *
+ * Contact information:  Silicon Graphics, Inc., 1500 Crittenden Lane,
+ * Mountain View, CA  94043, or:
+ * 
+ * http://www.sgi.com 
+ * 
+ * For further information regarding this notice, see: 
+ * 
+ * http://oss.sgi.com/projects/GenInfo/NoticeExplan
+ */
+
+/*
+ * Data structure definitions and function prototypes used to implement
+ * process aggregates (paggs).
+ *
+ * Paggs provides a generalized way to implement process groupings or
+ * containers.  Modules use these functions to register with the kernel as
+ * providers of process aggregation containers. The pagg data structures
+ * define the callback functions and data access pointers back into the
+ * pagg modules.
+ */
+
+#ifndef _LINUX_PAGG_H
+#define _LINUX_PAGG_H
+
+#include <linux/sched.h>
+
+#ifdef CONFIG_PAGG
+
+#define PAGG_NAMELN	32		/* Max chars in PAGG module name */
+
+
+/**
+ * INIT_PAGG_LIST - used to initialize a pagg_list structure after declaration 
+ * @_l: Task struct to init the pagg_list and semaphore in
+ * 
+ */
+#define INIT_PAGG_LIST(_l)						\
+do {									\
+	INIT_LIST_HEAD(&(_l)->pagg_list);					\
+	init_rwsem(&(_l)->pagg_sem);						\
+} while(0)
+	
+
+/*
+ * Used by task_struct to manage list of pagg attachments for the process.  
+ * Each pagg provides the link between the process and the 
+ * correct pagg container.
+ *
+ * STRUCT MEMBERS:
+ *     hook:	Reference to pagg module structure.  That struct
+ *     		holds the name key and function pointers.
+ *     data:	Opaque data pointer - defined by pagg modules.
+ *     entry:	List pointers
+ */
+struct pagg {
+       struct pagg_hook	*hook;
+       void		*data;
+       struct list_head	entry;
+};
+
+/*
+ * Used by pagg modules to define the callback functions into the 
+ * module.
+ *
+ * STRUCT MEMBERS:
+ *     name:           The name of the pagg container type provided by
+ *                     the module. This will be set by the pagg module.
+ *     attach:         Function pointer to function used when attaching
+ *                     a process to the pagg container referenced by 
+ *                     this struct.
+ *     detach:         Function pointer to function used when detaching
+ *                     a process to the pagg container referenced by 
+ *                     this struct.
+ *     init:           Function pointer to initialization function.  This
+ *                     function is used when the module is loaded to attach
+ *                     existing processes to a default container as defined by
+ *                     the pagg module. This is optional and may be set to 
+ *                     NULL if it is not needed by the pagg module.
+ *     data:           Opaque data pointer - defined by pagg modules.
+ *     module:         Pointer to kernel module struct.  Used to increment & 
+ *                     decrement the use count for the module.
+ *     entry:	       List pointers
+ *     exec:           Function pointer to function used when a process
+ *                     in the pagg container exec's a new process. This
+ *                     is optional and may be set to NULL if it is not 
+ *                     needed by the pagg module.
+ *     refcnt:         Keep track of user count of the pagg hook
+ */
+struct pagg_hook {
+       struct module	*module;
+       char		*name;	/* Name Key - restricted to 32 characters */
+       void		*data;	/* Opaque module specific data */
+       struct list_head	entry;	/* List pointers */
+		 atomic_t refcnt; /* usage counter */
+       int		(*init)(struct task_struct *, struct pagg *);
+       int		(*attach)(struct task_struct *, struct pagg *, void*);
+       void		(*detach)(struct task_struct *, struct pagg *);
+       void		(*exec)(struct task_struct *, struct pagg *);
+};
+
+
+/* Kernel service functions for providing PAGG support */
+extern struct pagg *pagg_get(struct task_struct *task, char *key);
+extern struct pagg *pagg_alloc(struct task_struct *task, 
+			       struct pagg_hook *pt);
+extern void pagg_free(struct pagg *pagg);
+extern int pagg_hook_register(struct pagg_hook *pt_new);
+extern int pagg_hook_unregister(struct pagg_hook *pt_old);
+extern void __pagg_attach(struct task_struct *to_task, 
+			 struct task_struct *from_task);
+extern void __pagg_detach(struct task_struct *task);
+extern int __pagg_exec(struct task_struct *task);
+
+/**
+ * pagg_attach - child inherits attachment to pagg containers of its parent
+ * @child: child task - to inherit
+ * @parent: parenet task - child inherits pagg containers from this parent
+ * 
+ * function used when a child process must inherit attachment to pagg
+ * containers from the parent.
+ *
+ */
+static inline void pagg_attach(struct task_struct *child, 
+			      struct task_struct *parent)
+{
+	INIT_PAGG_LIST(child);
+	if (!list_empty(&parent->pagg_list))
+		__pagg_attach(child, parent);
+	return;
+}
+
+
+/**
+ * pagg_detach - Detach a process from a pagg container it is a member of
+ * @task: The task the pagg will be detached from
+ *
+ */
+static inline void pagg_detach(struct task_struct *task)
+{
+	if (!list_empty(&task->pagg_list))
+		__pagg_detach(task);
+}
+
+/**
+ * pagg_exec - Used when a process exec's
+ * @task: The process doing the exec
+ *
+ */
+static inline void pagg_exec(struct task_struct *task)
+{
+	if (!list_empty(&task->pagg_list))
+		__pagg_exec(task);
+}
+
+/** 
+ * INIT_TASK_PAGG - Used in INIT_TASK to set the head and sem of pagg_list
+ * @tsk: The task work with
+ *
+ * Marco Used in INIT_TASK to set the head and sem of pagg_list.
+ * If CONFIG_PAGG is off, it is defined as an empty macro below.
+ *
+ */
+#define INIT_TASK_PAGG(tsk) \
+	.pagg_list = LIST_HEAD_INIT(tsk.pagg_list),     \
+	.pagg_sem  = __RWSEM_INITIALIZER(tsk.pagg_sem)  
+
+#else  /* CONFIG_PAGG */
+
+/* 
+ * Replacement macros used when PAGG (Process Aggregates) support is not
+ * compiled into the kernel.
+ */
+#define INIT_TASK_PAGG(tsk)
+#define INIT_PAGG_LIST(l) do { } while(0)
+#define pagg_attach(ct, pt)  do { } while(0)
+#define pagg_detach(t)  do {  } while(0)     
+#define pagg_exec(t)  do {  } while(0)     
+
+#endif /* CONFIG_PAGG */
+
+#endif /* _LINUX_PAGG_H */
Index: linux/include/linux/sched.h
===================================================================
--- linux.orig/include/linux/sched.h
+++ linux/include/linux/sched.h
@@ -513,6 +513,13 @@
   	struct mempolicy *mempolicy;
   	short il_next;		/* could be shared with used_math */
 #endif
+
+#ifdef CONFIG_PAGG
+/* List of pagg (process aggregate) attachments */
+	struct list_head pagg_list;
+	struct rw_semaphore pagg_sem;
+#endif
+
 };
 
 static inline pid_t process_group(struct task_struct *tsk)
Index: linux/init/Kconfig
===================================================================
--- linux.orig/init/Kconfig
+++ linux/init/Kconfig
@@ -121,6 +121,14 @@
 	  up to the user level program to do useful things with this
 	  information.  This is generally a good idea, so say Y.
 
+config PAGG
+	bool "Support for process aggregates (PAGGs)"
+	help
+     Say Y here if you will be loading modules which provide support
+     for process aggregate containers.  Examples of such modules include the
+     Linux Jobs module and the Linux Array Sessions module.  If you will not 
+     be using such modules, say N.
+
 config SYSCTL
 	bool "Sysctl support"
 	---help---
Index: linux/kernel/Makefile
===================================================================
--- linux.orig/kernel/Makefile
+++ linux/kernel/Makefile
@@ -18,6 +18,7 @@
 obj-$(CONFIG_PM) += power/
 obj-$(CONFIG_BSD_PROCESS_ACCT) += acct.o
 obj-$(CONFIG_COMPAT) += compat.o
+obj-$(CONFIG_PAGG) += pagg.o
 obj-$(CONFIG_IKCONFIG) += configs.o
 obj-$(CONFIG_IKCONFIG_PROC) += configs.o
 obj-$(CONFIG_STOP_MACHINE) += stop_machine.o
Index: linux/kernel/fork.c
===================================================================
--- linux.orig/kernel/fork.c
+++ linux/kernel/fork.c
@@ -36,6 +36,7 @@
 #include <linux/mount.h>
 #include <linux/audit.h>
 #include <linux/rmap.h>
+#include <linux/pagg.h>
 
 #include <asm/pgtable.h>
 #include <asm/pgalloc.h>
@@ -87,6 +88,8 @@
 	WARN_ON(atomic_read(&tsk->usage));
 	WARN_ON(tsk == current);
 
+	pagg_detach(tsk);
+
 	if (unlikely(tsk->audit_context))
 		audit_free(tsk);
 	security_task_free(tsk);
@@ -236,6 +239,9 @@
 
 	init_task.rlim[RLIMIT_NPROC].rlim_cur = max_threads/2;
 	init_task.rlim[RLIMIT_NPROC].rlim_max = max_threads/2;
+
+	/* Initialize the pagg list in pid 0 before it can clone itself. */
+	INIT_PAGG_LIST(current);
 }
 
 static struct task_struct *dup_task_struct(struct task_struct *orig)
@@ -1023,6 +1029,12 @@
 	sched_fork(p);
 
 	/*
+	 * call pagg modules to properly attach new process to the same
+	 * process aggregate containers as the parent process.
+	 */
+	pagg_attach(p, current);
+
+	/*
 	 * Ok, make it visible to the rest of the system.
 	 * We dont wake it up yet.
 	 */
Index: linux/kernel/pagg.c
===================================================================
--- /dev/null
+++ linux/kernel/pagg.c
@@ -0,0 +1,477 @@
+/* 
+ * PAGG (Process Aggregates) interface
+ *
+ * 
+ * Copyright (c) 2000-2004 Silicon Graphics, Inc.  All Rights Reserved.
+ *
+ * This program 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; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
+ *
+ * Contact information:  Silicon Graphics, Inc., 1500 Crittenden Lane,
+ * Mountain View, CA  94043, or:
+ * 
+ * http://www.sgi.com 
+ */
+
+#include <linux/config.h>
+#include <linux/slab.h>
+#include <linux/sched.h>
+#include <linux/module.h>
+#include <linux/pagg.h>
+#include <asm/semaphore.h>
+
+/* list of pagg hook entries that reference the "module" implementations */
+static LIST_HEAD(pagg_hook_list);
+static DECLARE_RWSEM(pagg_hook_list_sem);
+
+
+/**
+ * pagg_get - get a pagg given a search key
+ * @task: We examine the pagg_list from the given task
+ * @key: Key name of pagg we wish to retrieve
+ *
+ * Given a pagg_list list structure, this function will return
+ * a pointer to the pagg struct that matches the search
+ * key.  If the key is not found, the function will return NULL.
+ *
+ * The caller should hold at least a read lock on the pagg_list
+ * for task using down_read(&task->pagg_list.sem).
+ *
+ */
+struct pagg *
+pagg_get(struct task_struct *task, char *key)
+{
+	struct pagg *pagg;
+
+	list_for_each_entry(pagg, &task->pagg_list, entry) {
+		if (!strcmp(pagg->hook->name,key))
+			return pagg;
+	}
+	return NULL;
+}
+
+
+/**
+ * pagg_alloc - Insert a new pagg in to the pagg_list for a task
+ * @task: Task we want to insert the pagg in to
+ * @pagg_hook: Pagg hook to associate with the new pagg
+ *
+ * Given a task and a pagg hook, this function will allocate
+ * a new pagg structure, initialize the settings, and insert the pagg into
+ * the pagg_list for the task.
+ *
+ * The caller for this function should hold at least a read lock on the
+ * pagg_hook_list_sem - or ensure that the pagg hook entry cannot be 
+ * removed. If this function was called from the pagg module (usually the
+ * case), then the caller need not hold this lock. The caller should hold 
+ * a write lock on for the tasks pagg_sem.  This can be locked using 
+ * down_write(&task->pagg_sem)
+ * 
+ */
+struct pagg *
+pagg_alloc(struct task_struct *task, struct pagg_hook *pagg_hook)
+{
+	struct pagg *pagg;
+
+	pagg = kmalloc(sizeof(struct pagg), GFP_KERNEL);
+	if (!pagg)
+		return NULL;
+
+	pagg->hook = pagg_hook;
+	pagg->data = NULL;
+	atomic_inc(&pagg_hook->refcnt);  /* Increase hook's reference count */
+	list_add_tail(&pagg->entry, &task->pagg_list);
+	return pagg;
+}
+
+
+/**
+ * pagg_free - Delete pagg from the list and free its memory
+ * @pagg: The pagg to free
+ *
+ * This function will ensure the pagg is deleted form 
+ * the list of pagg entries for the task. Finally, the memory for the 
+ * pagg is discarded.
+ *
+ * The caller of this function should hold a write lock on the pagg_sem
+ * for the task. This can be locked using down_write(&task->pagg_sem).
+ *
+ * Prior to calling pagg_free, the pagg should have been detached from the
+ * pagg container represented by this pagg.  That is usually done using
+ * p->hook->detach(task, pagg);
+ * 
+ */
+void
+pagg_free(struct pagg *pagg) 
+{
+	atomic_dec(&pagg->hook->refcnt); /* decr the reference count on the hook */
+	list_del(&pagg->entry);
+	kfree(pagg);
+}
+
+
+/**
+ * get_pagg_hook - Get the pagg hook matching the requested name
+ * @key: The name of the pagg hook to get
+ *
+ * Given a pagg hook name key, this function will return a pointer
+ * to the pagg_hook struct that matches the name.
+ * 
+ * You should hold either the write or read lock for pagg_hook_list_sem
+ * before using this function.  This will ensure that the pagg_hook_list
+ * does not change while iterating through the list entries.
+ *
+ */
+static struct pagg_hook *
+get_pagg_hook(char *key)
+{
+	struct pagg_hook *pagg_hook;
+
+	list_for_each_entry(pagg_hook, &pagg_hook_list, entry) {
+		if (!strcmp(pagg_hook->name, key)) {
+			return pagg_hook;
+		}
+	}
+	return NULL;
+}
+
+/**
+ * remove_client_paggs_from_all_tasks - Remove all paggs associated with hook
+ * @php: Pagg hook associated with paggs to purge
+ * 
+ * Given a pagg hook, this function will remove all paggs associated with that 
+ * pagg hook from all tasks calling the provided function on each pagg.
+ * 
+ * If there is a detach function associated with the pagg, it is called
+ * before the pagg is freed.
+ *
+ * This is meant to be used by pagg_hook_register and pagg_hook_unregister
+ *
+ */
+static void
+remove_client_paggs_from_all_tasks(struct pagg_hook *php)
+{
+	if (php == NULL)
+		return;
+
+	/* Because of internal race conditions we can't gaurantee
+	 * getting every task in just one pass so we just keep going
+	 * until there are no tasks with paggs from this hook attached.
+	 * The inefficiency of this should be tempered by the fact that this
+	 * happens at most once for each registered client.
+	 */
+	while (atomic_read(&php->refcnt) != 0) {
+		struct task_struct *p = NULL;
+
+		read_lock(&tasklist_lock);
+		for_each_process(p) {
+			struct pagg *paggp;
+
+			get_task_struct(p);
+			read_unlock(&tasklist_lock);
+			down_write(&p->pagg_sem);
+			paggp = pagg_get(p, php->name);
+			if (paggp != NULL) {
+				(void)php->detach(p, paggp);
+				pagg_free(paggp);
+			}
+			up_write(&p->pagg_sem);
+			read_lock(&tasklist_lock);
+
+			/* If a PAGG got removed from the list while we're going through
+			 * each process, the tasks list for the process would be empty.  In
+			 * that case, break out of this for_each_process so we can do it
+			 * again. */
+			if (list_empty(&p->tasks)) {
+				put_task_struct(p);
+				break;
+			} else
+				put_task_struct(p);
+
+		}
+		read_unlock(&tasklist_lock);
+	}
+}
+
+/**
+ * pagg_hook_register - Register a new pagg hook and enter it the list
+ * @pagg_hook_new: The new pagg hook to register
+ *
+ * Used to register a new pagg hook and enter it into the pagg_hook_list.
+ * The service name for a pagg hook is restricted to 32 characters.
+ *
+ * If an "init()" function is supplied in the hook being registered then a
+ * pagg will be attached to all existing tasks and the supplied "init()"
+ * function will be applied to it.  If any call to the supplied "init()"
+ * function returns a non zero result the registration will be aborted. As
+ * part of the abort process, all paggs belonging to the new client will be
+ * removed from all tasks and the supplied "detach()" function will be
+ * called on them.  
+ *
+ * If a memory error is encountered, the pagg hook is unregistered and any
+ * tasks that have been attached to the initial pagg container are detached
+ * from that container.
+ *
+ */
+int
+pagg_hook_register(struct pagg_hook *pagg_hook_new)
+{
+	struct pagg_hook *pagg_hook = NULL;
+
+	/* Add new pagg module to access list */
+	if (!pagg_hook_new)
+		return -EINVAL;			/* error */
+	if (!list_empty(&pagg_hook_new->entry))
+		return -EINVAL;			/* error */
+	if (pagg_hook_new->name == NULL || strlen(pagg_hook_new->name) > PAGG_NAMELN)
+		return -EINVAL;			/* error */
+
+	/* Try to insert new hook entry into the pagg hook list */
+	down_write(&pagg_hook_list_sem);
+
+	pagg_hook = get_pagg_hook(pagg_hook_new->name);
+
+	if (pagg_hook) {
+		up_write(&pagg_hook_list_sem);
+		printk(KERN_WARNING "Attempt to register duplicate"
+				" PAGG support (name=%s)\n", pagg_hook_new->name);
+		return -EBUSY;
+	}
+
+	/* Okay, we can insert into the pagg hook list */
+	list_add_tail(&pagg_hook_new->entry, &pagg_hook_list);
+	/* set the ref count to zero */
+	atomic_set(&pagg_hook_new->refcnt, 0);
+
+	/* Now we can call the initializer function (if present) for each task */
+	if (pagg_hook_new->init != NULL) {
+		int init_result = 0;
+		int task_exited;
+
+		/* Because of internal race conditions we can't gaurantee
+		 * getting every task in just one pass so we just keep going
+		 * until we don't find any unitialized tasks.  The inefficiency
+		 * of this should be tempered by the fact that this happens
+		 * at most once for each registered client.
+		 */
+		do {
+			struct task_struct *p = NULL;
+
+			read_lock(&tasklist_lock);
+			for_each_process(p) {
+				struct pagg *paggp;
+
+				get_task_struct(p);
+				read_unlock(&tasklist_lock);
+				down_write(&p->pagg_sem);
+				paggp = pagg_get(p, pagg_hook_new->name);
+				if (paggp == NULL) {
+					paggp = pagg_alloc(p, pagg_hook_new);
+					if (paggp != NULL)
+						init_result = pagg_hook_new->init(p, paggp);
+					else
+						init_result = -ENOMEM;
+				}
+				up_write(&p->pagg_sem);
+				read_lock(&tasklist_lock);
+				/* Like in remove_client_paggs_from_all_tasks, if the task
+				 * disappeared on us while we were going through the
+				 * for_each_process loop, we need to start over with that loop.
+				 * That's why we have the list_empty here */
+				task_exited = list_empty(&p->tasks);
+				put_task_struct(p);
+				if ((init_result != 0) || task_exited) {
+					break;
+				}
+			}
+			read_unlock(&tasklist_lock);
+		} while ((init_result == 0) && task_exited);
+
+		/*
+		 * if anything went wrong during initialisation abandon the
+		 * registration process
+		 */
+		if (init_result != 0) {
+			remove_client_paggs_from_all_tasks(pagg_hook_new);
+			list_del_init(&pagg_hook_new->entry);
+			up_write(&pagg_hook_list_sem);
+
+			printk(KERN_WARNING "Registering PAGG support for"
+				" (name=%s) failed\n", pagg_hook_new->name);
+
+			return init_result; /* hook init function error result */
+		}
+	}
+
+	up_write(&pagg_hook_list_sem);
+
+	printk(KERN_INFO "Registering PAGG support for (name=%s)\n",
+			pagg_hook_new->name);
+
+	return 0;					/* success */
+
+}
+
+/**
+ * pagg_hook_unregister - Unregister pagg hook and remove it from the list
+ * @pagg_hook_old: The hook to unregister and remove
+ *
+ * Used to unregister pagg hooks and remove them from the pagg_hook_list.
+ * Once the pagg hook entry in the pagg_hook_list is found, paggs associated
+ * with the hook (if any) will have their detach function called and will
+ * be detached.
+ * 
+ */
+int
+pagg_hook_unregister(struct pagg_hook *pagg_hook_old)
+{
+	struct pagg_hook *pagg_hook;
+
+	/* Check the validity of the arguments */
+	if (!pagg_hook_old)
+		return -EINVAL;			/* error */
+	if (list_empty(&pagg_hook_old->entry))
+		return -EINVAL;			/* error */
+	if (pagg_hook_old->name == NULL)
+		return -EINVAL;			/* error */
+
+	down_write(&pagg_hook_list_sem);
+
+	pagg_hook = get_pagg_hook(pagg_hook_old->name);
+
+	if (pagg_hook && pagg_hook == pagg_hook_old) {
+		remove_client_paggs_from_all_tasks(pagg_hook);
+		list_del_init(&pagg_hook->entry);
+		up_write(&pagg_hook_list_sem);
+
+		printk(KERN_INFO "Unregistering PAGG support for"
+				" (name=%s)\n", pagg_hook_old->name);
+
+		return 0;			/* success */
+	}
+
+	up_write(&pagg_hook_list_sem);
+
+	printk(KERN_WARNING "Attempt to unregister PAGG support (name=%s)"
+			" failed - not found\n", pagg_hook_old->name);
+	
+	return -EINVAL;				/* error */
+}
+
+
+/**
+ * __pagg_attach - Attach a new task to the same containers of its parent
+ * @to_task: The child task that will inherit the parent's containers
+ * @from_task: The parent task 
+ *
+ * Used to attach a new task to the same pagg containers to which it's parent
+ * is attached.
+ *
+ * The "from" argument is the parent task.  The "to" argument is the child
+ * task. 
+ *
+ */
+void 
+__pagg_attach(struct task_struct *to_task, struct task_struct *from_task)
+{
+	struct pagg *from_pagg;
+
+	/* lock the parents pagg_list we are copying from */
+	down_read(&from_task->pagg_sem); /* read lock the pagg list */
+
+	list_for_each_entry(from_pagg, &from_task->pagg_list, entry) {
+		struct pagg *to_pagg = NULL;
+
+		to_pagg = pagg_alloc(to_task, from_pagg->hook);
+		if (!to_pagg) {
+			goto error_return;
+		}
+		if (to_pagg->hook->attach(to_task, to_pagg, from_pagg->data) != 0 ) 
+			goto error_return;
+	}
+
+	up_read(&from_task->pagg_sem); /* unlock the pagg list */
+
+	return;					/* success */
+
+  error_return:
+	/* 
+	 * Clean up all the pagg attachments made on behalf of the new
+	 * task.  Set new task pagg ptr to NULL for return.
+	 */
+	up_read(&from_task->pagg_sem); /* unlock the pagg list */
+	__pagg_detach(to_task);
+	return;				/* failure */
+}
+
+/**
+ * __pagg_detach - Detach a task from all pagg containers it is attached to
+ * @task: Task to detach from pagg containers
+ *
+ * Used to detach a task from all pagg containers to which it is attached.
+ * 
+ */
+void 
+__pagg_detach(struct task_struct *task)
+{
+	struct pagg *pagg;
+	struct pagg *paggtmp;
+
+	/* Remove ref. to paggs from task immediately */
+	down_write(&task->pagg_sem); /* write lock pagg list */
+
+	list_for_each_entry_safe(pagg, paggtmp, &task->pagg_list, entry) {
+		pagg->hook->detach(task, pagg);
+		pagg_free(pagg);
+	}
+                                                                                
+	up_write(&task->pagg_sem); /* write unlock the pagg list */
+                                                                                
+	return;   /* 0 = success, else return last code for failure */
+}
+
+
+/**
+ * __pagg_exec - Execute callback when a process in a container execs
+ * @task: We go through the pagg list in the given task
+ *
+ * Used to when a process that is in a pagg container does an exec.
+ *
+ * The "from" argument is the task.  The "name" argument is the name
+ * of the process being exec'ed.
+ *
+ */
+int 
+__pagg_exec(struct task_struct *task) 
+{
+	struct pagg	*pagg;
+
+	/* lock the parents pagg_list we are copying from */
+	down_read(&task->pagg_sem); /* lock the pagg list */
+
+	list_for_each_entry(pagg, &task->pagg_list, entry) {
+		if (pagg->hook->exec) /* conditional because it's optional */
+			pagg->hook->exec(task, pagg);
+	}
+
+	up_read(&task->pagg_sem); /* unlock the pagg list */
+	return 0;
+}
+
+
+EXPORT_SYMBOL(pagg_get);
+EXPORT_SYMBOL(pagg_alloc);
+EXPORT_SYMBOL(pagg_free);
+EXPORT_SYMBOL(pagg_hook_register);
+EXPORT_SYMBOL(pagg_hook_unregister);