2.6.24-rc7

 kernel

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
new file mode 100644
index 0000000..1a3c239
--- /dev/null
+++ b/kernel/cgroup.c
@@ -0,0 +1,2803 @@
+/*
+ *  Generic process-grouping system.
+ *
+ *  Based originally on the cpuset system, extracted by Paul Menage
+ *  Copyright (C) 2006 Google, Inc
+ *
+ *  Copyright notices from the original cpuset code:
+ *  --------------------------------------------------
+ *  Copyright (C) 2003 BULL SA.
+ *  Copyright (C) 2004-2006 Silicon Graphics, Inc.
+ *
+ *  Portions derived from Patrick Mochel's sysfs code.
+ *  sysfs is Copyright (c) 2001-3 Patrick Mochel
+ *
+ *  2003-10-10 Written by Simon Derr.
+ *  2003-10-22 Updates by Stephen Hemminger.
+ *  2004 May-July Rework by Paul Jackson.
+ *  ---------------------------------------------------
+ *
+ *  This file is subject to the terms and conditions of the GNU General Public
+ *  License.  See the file COPYING in the main directory of the Linux
+ *  distribution for more details.
+ */
+
+#include <linux/cgroup.h>
+#include <linux/errno.h>
+#include <linux/fs.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/mm.h>
+#include <linux/mutex.h>
+#include <linux/mount.h>
+#include <linux/pagemap.h>
+#include <linux/proc_fs.h>
+#include <linux/rcupdate.h>
+#include <linux/sched.h>
+#include <linux/backing-dev.h>
+#include <linux/seq_file.h>
+#include <linux/slab.h>
+#include <linux/magic.h>
+#include <linux/spinlock.h>
+#include <linux/string.h>
+#include <linux/sort.h>
+#include <linux/kmod.h>
+#include <linux/delayacct.h>
+#include <linux/cgroupstats.h>
+
+#include <asm/atomic.h>
+
+static DEFINE_MUTEX(cgroup_mutex);
+
+/* Generate an array of cgroup subsystem pointers */
+#define SUBSYS(_x) &_x ## _subsys,
+
+static struct cgroup_subsys *subsys[] = {
+#include <linux/cgroup_subsys.h>
+};
+
+/*
+ * A cgroupfs_root represents the root of a cgroup hierarchy,
+ * and may be associated with a superblock to form an active
+ * hierarchy
+ */
+struct cgroupfs_root {
+   struct super_block *sb;
+
+   /*
+    * The bitmask of subsystems intended to be attached to this
+    * hierarchy
+    */
+   unsigned long subsys_bits;
+
+   /* The bitmask of subsystems currently attached to this hierarchy */
+   unsigned long actual_subsys_bits;
+
+   /* A list running through the attached subsystems */
+   struct list_head subsys_list;
+
+   /* The root cgroup for this hierarchy */
+   struct cgroup top_cgroup;
+
+   /* Tracks how many cgroups are currently defined in hierarchy.*/
+   int number_of_cgroups;
+
+   /* A list running through the mounted hierarchies */
+   struct list_head root_list;
+
+   /* Hierarchy-specific flags */
+   unsigned long flags;
+
+   /* The path to use for release notifications. No locking
+    * between setting and use - so if userspace updates this
+    * while child cgroups exist, you could miss a
+    * notification. We ensure that it's always a valid
+    * NUL-terminated string */
+   char release_agent_path[PATH_MAX];
+};
+
+
+/*
+ * The "rootnode" hierarchy is the "dummy hierarchy", reserved for the
+ * subsystems that are otherwise unattached - it never has more than a
+ * single cgroup, and all tasks are part of that cgroup.
+ */
+static struct cgroupfs_root rootnode;
+
+/* The list of hierarchy roots */
+
+static LIST_HEAD(roots);
+static int root_count;
+
+/* dummytop is a shorthand for the dummy hierarchy's top cgroup */
+#define dummytop (&rootnode.top_cgroup)
+
+/* This flag indicates whether tasks in the fork and exit paths should
+ * take callback_mutex and check for fork/exit handlers to call. This
+ * avoids us having to do extra work in the fork/exit path if none of the
+ * subsystems need to be called.
+ */
+static int need_forkexit_callback;
+
+/* bits in struct cgroup flags field */
+enum {
+   /* Control Group is dead */
+   CGRP_REMOVED,
+   /* Control Group has previously had a child cgroup or a task,
+    * but no longer (only if CGRP_NOTIFY_ON_RELEASE is set) */
+   CGRP_RELEASABLE,
+   /* Control Group requires release notifications to userspace */
+   CGRP_NOTIFY_ON_RELEASE,
+};
+
+/* convenient tests for these bits */
+inline int cgroup_is_removed(const struct cgroup *cgrp)
+{
+   return test_bit(CGRP_REMOVED, &cgrp->flags);
+}
+
+/* bits in struct cgroupfs_root flags field */
+enum {
+   ROOT_NOPREFIX, /* mounted subsystems have no named prefix */
+};
+
+inline int cgroup_is_releasable(const struct cgroup *cgrp)
+{
+   const int bits =
+      (1 << CGRP_RELEASABLE) |
+      (1 << CGRP_NOTIFY_ON_RELEASE);
+   return (cgrp->flags & bits) == bits;
+}
+
+inline int notify_on_release(const struct cgroup *cgrp)
+{
+   return test_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+}
+
+/*
+ * for_each_subsys() allows you to iterate on each subsystem attached to
+ * an active hierarchy
+ */
+#define for_each_subsys(_root, _ss) \
+list_for_each_entry(_ss, &_root->subsys_list, sibling)
+
+/* for_each_root() allows you to iterate across the active hierarchies */
+#define for_each_root(_root) \
+list_for_each_entry(_root, &roots, root_list)
+
+/* the list of cgroups eligible for automatic release. Protected by
+ * release_list_lock */
+static LIST_HEAD(release_list);
+static DEFINE_SPINLOCK(release_list_lock);
+static void cgroup_release_agent(struct work_struct *work);
+static DECLARE_WORK(release_agent_work, cgroup_release_agent);
+static void check_for_release(struct cgroup *cgrp);
+
+/* Link structure for associating css_set objects with cgroups */
+struct cg_cgroup_link {
+   /*
+    * List running through cg_cgroup_links associated with a
+    * cgroup, anchored on cgroup->css_sets
+    */
+   struct list_head cgrp_link_list;
+   /*
+    * List running through cg_cgroup_links pointing at a
+    * single css_set object, anchored on css_set->cg_links
+    */
+   struct list_head cg_link_list;
+   struct css_set *cg;
+};
+
+/* The default css_set - used by init and its children prior to any
+ * hierarchies being mounted. It contains a pointer to the root state
+ * for each subsystem. Also used to anchor the list of css_sets. Not
+ * reference-counted, to improve performance when child cgroups
+ * haven't been created.
+ */
+
+static struct css_set init_css_set;
+static struct cg_cgroup_link init_css_set_link;
+
+/* css_set_lock protects the list of css_set objects, and the
+ * chain of tasks off each css_set.  Nests outside task->alloc_lock
+ * due to cgroup_iter_start() */
+static DEFINE_RWLOCK(css_set_lock);
+static int css_set_count;
+
+/* We don't maintain the lists running through each css_set to its
+ * task until after the first call to cgroup_iter_start(). This
+ * reduces the fork()/exit() overhead for people who have cgroups
+ * compiled into their kernel but not actually in use */
+static int use_task_css_set_links;
+
+/* When we create or destroy a css_set, the operation simply
+ * takes/releases a reference count on all the cgroups referenced
+ * by subsystems in this css_set. This can end up multiple-counting
+ * some cgroups, but that's OK - the ref-count is just a
+ * busy/not-busy indicator; ensuring that we only count each cgroup
+ * once would require taking a global lock to ensure that no
+ * subsystems moved between hierarchies while we were doing so.
+ *
+ * Possible TODO: decide at boot time based on the number of
+ * registered subsystems and the number of CPUs or NUMA nodes whether
+ * it's better for performance to ref-count every subsystem, or to
+ * take a global lock and only add one ref count to each hierarchy.
+ */
+
+/*
+ * unlink a css_set from the list and free it
+ */
+static void unlink_css_set(struct css_set *cg)
+{
+   write_lock(&css_set_lock);
+   list_del(&cg->list);
+   css_set_count--;
+   while (!list_empty(&cg->cg_links)) {
+      struct cg_cgroup_link *link;
+      link = list_entry(cg->cg_links.next,
+              struct cg_cgroup_link, cg_link_list);
+      list_del(&link->cg_link_list);
+      list_del(&link->cgrp_link_list);
+      kfree(link);
+   }
+   write_unlock(&css_set_lock);
+}
+
+static void __release_css_set(struct kref *k, int taskexit)
+{
+   int i;
+   struct css_set *cg = container_of(k, struct css_set, ref);
+
+   unlink_css_set(cg);
+
+   rcu_read_lock();
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup *cgrp = cg->subsys[i]->cgroup;
+      if (atomic_dec_and_test(&cgrp->count) &&
+          notify_on_release(cgrp)) {
+         if (taskexit)
+            set_bit(CGRP_RELEASABLE, &cgrp->flags);
+         check_for_release(cgrp);
+      }
+   }
+   rcu_read_unlock();
+   kfree(cg);
+}
+
+static void release_css_set(struct kref *k)
+{
+   __release_css_set(k, 0);
+}
+
+static void release_css_set_taskexit(struct kref *k)
+{
+   __release_css_set(k, 1);
+}
+
+/*
+ * refcounted get/put for css_set objects
+ */
+static inline void get_css_set(struct css_set *cg)
+{
+   kref_get(&cg->ref);
+}
+
+static inline void put_css_set(struct css_set *cg)
+{
+   kref_put(&cg->ref, release_css_set);
+}
+
+static inline void put_css_set_taskexit(struct css_set *cg)
+{
+   kref_put(&cg->ref, release_css_set_taskexit);
+}
+
+/*
+ * find_existing_css_set() is a helper for
+ * find_css_set(), and checks to see whether an existing
+ * css_set is suitable. This currently walks a linked-list for
+ * simplicity; a later patch will use a hash table for better
+ * performance
+ *
+ * oldcg: the cgroup group that we're using before the cgroup
+ * transition
+ *
+ * cgrp: the cgroup that we're moving into
+ *
+ * template: location in which to build the desired set of subsystem
+ * state objects for the new cgroup group
+ */
+
+static struct css_set *find_existing_css_set(
+   struct css_set *oldcg,
+   struct cgroup *cgrp,
+   struct cgroup_subsys_state *template[])
+{
+   int i;
+   struct cgroupfs_root *root = cgrp->root;
+   struct list_head *l = &init_css_set.list;
+
+   /* Built the set of subsystem state objects that we want to
+    * see in the new css_set */
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      if (root->subsys_bits & (1ull << i)) {
+         /* Subsystem is in this hierarchy. So we want
+          * the subsystem state from the new
+          * cgroup */
+         template[i] = cgrp->subsys[i];
+      } else {
+         /* Subsystem is not in this hierarchy, so we
+          * don't want to change the subsystem state */
+         template[i] = oldcg->subsys[i];
+      }
+   }
+
+   /* Look through existing cgroup groups to find one to reuse */
+   do {
+      struct css_set *cg =
+         list_entry(l, struct css_set, list);
+
+      if (!memcmp(template, cg->subsys, sizeof(cg->subsys))) {
+         /* All subsystems matched */
+         return cg;
+      }
+      /* Try the next cgroup group */
+      l = l->next;
+   } while (l != &init_css_set.list);
+
+   /* No existing cgroup group matched */
+   return NULL;
+}
+
+/*
+ * allocate_cg_links() allocates "count" cg_cgroup_link structures
+ * and chains them on tmp through their cgrp_link_list fields. Returns 0 on
+ * success or a negative error
+ */
+
+static int allocate_cg_links(int count, struct list_head *tmp)
+{
+   struct cg_cgroup_link *link;
+   int i;
+   INIT_LIST_HEAD(tmp);
+   for (i = 0; i < count; i++) {
+      link = kmalloc(sizeof(*link), GFP_KERNEL);
+      if (!link) {
+         while (!list_empty(tmp)) {
+            link = list_entry(tmp->next,
+                    struct cg_cgroup_link,
+                    cgrp_link_list);
+            list_del(&link->cgrp_link_list);
+            kfree(link);
+         }
+         return -ENOMEM;
+      }
+      list_add(&link->cgrp_link_list, tmp);
+   }
+   return 0;
+}
+
+static void free_cg_links(struct list_head *tmp)
+{
+   while (!list_empty(tmp)) {
+      struct cg_cgroup_link *link;
+      link = list_entry(tmp->next,
+              struct cg_cgroup_link,
+              cgrp_link_list);
+      list_del(&link->cgrp_link_list);
+      kfree(link);
+   }
+}
+
+/*
+ * find_css_set() takes an existing cgroup group and a
+ * cgroup object, and returns a css_set object that's
+ * equivalent to the old group, but with the given cgroup
+ * substituted into the appropriate hierarchy. Must be called with
+ * cgroup_mutex held
+ */
+
+static struct css_set *find_css_set(
+   struct css_set *oldcg, struct cgroup *cgrp)
+{
+   struct css_set *res;
+   struct cgroup_subsys_state *template[CGROUP_SUBSYS_COUNT];
+   int i;
+
+   struct list_head tmp_cg_links;
+   struct cg_cgroup_link *link;
+
+   /* First see if we already have a cgroup group that matches
+    * the desired set */
+   write_lock(&css_set_lock);
+   res = find_existing_css_set(oldcg, cgrp, template);
+   if (res)
+      get_css_set(res);
+   write_unlock(&css_set_lock);
+
+   if (res)
+      return res;
+
+   res = kmalloc(sizeof(*res), GFP_KERNEL);
+   if (!res)
+      return NULL;
+
+   /* Allocate all the cg_cgroup_link objects that we'll need */
+   if (allocate_cg_links(root_count, &tmp_cg_links) < 0) {
+      kfree(res);
+      return NULL;
+   }
+
+   kref_init(&res->ref);
+   INIT_LIST_HEAD(&res->cg_links);
+   INIT_LIST_HEAD(&res->tasks);
+
+   /* Copy the set of subsystem state objects generated in
+    * find_existing_css_set() */
+   memcpy(res->subsys, template, sizeof(res->subsys));
+
+   write_lock(&css_set_lock);
+   /* Add reference counts and links from the new css_set. */
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup *cgrp = res->subsys[i]->cgroup;
+      struct cgroup_subsys *ss = subsys[i];
+      atomic_inc(&cgrp->count);
+      /*
+       * We want to add a link once per cgroup, so we
+       * only do it for the first subsystem in each
+       * hierarchy
+       */
+      if (ss->root->subsys_list.next == &ss->sibling) {
+         BUG_ON(list_empty(&tmp_cg_links));
+         link = list_entry(tmp_cg_links.next,
+                 struct cg_cgroup_link,
+                 cgrp_link_list);
+         list_del(&link->cgrp_link_list);
+         list_add(&link->cgrp_link_list, &cgrp->css_sets);
+         link->cg = res;
+         list_add(&link->cg_link_list, &res->cg_links);
+      }
+   }
+   if (list_empty(&rootnode.subsys_list)) {
+      link = list_entry(tmp_cg_links.next,
+              struct cg_cgroup_link,
+              cgrp_link_list);
+      list_del(&link->cgrp_link_list);
+      list_add(&link->cgrp_link_list, &dummytop->css_sets);
+      link->cg = res;
+      list_add(&link->cg_link_list, &res->cg_links);
+   }
+
+   BUG_ON(!list_empty(&tmp_cg_links));
+
+   /* Link this cgroup group into the list */
+   list_add(&res->list, &init_css_set.list);
+   css_set_count++;
+   INIT_LIST_HEAD(&res->tasks);
+   write_unlock(&css_set_lock);
+
+   return res;
+}
+
+/*
+ * There is one global cgroup mutex. We also require taking
+ * task_lock() when dereferencing a task's cgroup subsys pointers.
+ * See "The task_lock() exception", at the end of this comment.
+ *
+ * A task must hold cgroup_mutex to modify cgroups.
+ *
+ * Any task can increment and decrement the count field without lock.
+ * So in general, code holding cgroup_mutex can't rely on the count
+ * field not changing.  However, if the count goes to zero, then only
+ * attach_task() can increment it again.  Because a count of zero
+ * means that no tasks are currently attached, therefore there is no
+ * way a task attached to that cgroup can fork (the other way to
+ * increment the count).  So code holding cgroup_mutex can safely
+ * assume that if the count is zero, it will stay zero. Similarly, if
+ * a task holds cgroup_mutex on a cgroup with zero count, it
+ * knows that the cgroup won't be removed, as cgroup_rmdir()
+ * needs that mutex.
+ *
+ * The cgroup_common_file_write handler for operations that modify
+ * the cgroup hierarchy holds cgroup_mutex across the entire operation,
+ * single threading all such cgroup modifications across the system.
+ *
+ * The fork and exit callbacks cgroup_fork() and cgroup_exit(), don't
+ * (usually) take cgroup_mutex.  These are the two most performance
+ * critical pieces of code here.  The exception occurs on cgroup_exit(),
+ * when a task in a notify_on_release cgroup exits.  Then cgroup_mutex
+ * is taken, and if the cgroup count is zero, a usermode call made
+ * to /sbin/cgroup_release_agent with the name of the cgroup (path
+ * relative to the root of cgroup file system) as the argument.
+ *
+ * A cgroup can only be deleted if both its 'count' of using tasks
+ * is zero, and its list of 'children' cgroups is empty.  Since all
+ * tasks in the system use _some_ cgroup, and since there is always at
+ * least one task in the system (init, pid == 1), therefore, top_cgroup
+ * always has either children cgroups and/or using tasks.  So we don't
+ * need a special hack to ensure that top_cgroup cannot be deleted.
+ *
+ *   The task_lock() exception
+ *
+ * The need for this exception arises from the action of
+ * attach_task(), which overwrites one tasks cgroup pointer with
+ * another.  It does so using cgroup_mutexe, however there are
+ * several performance critical places that need to reference
+ * task->cgroup without the expense of grabbing a system global
+ * mutex.  Therefore except as noted below, when dereferencing or, as
+ * in attach_task(), modifying a task'ss cgroup pointer we use
+ * task_lock(), which acts on a spinlock (task->alloc_lock) already in
+ * the task_struct routinely used for such matters.
+ *
+ * P.S.  One more locking exception.  RCU is used to guard the
+ * update of a tasks cgroup pointer by attach_task()
+ */
+
+/**
+ * cgroup_lock - lock out any changes to cgroup structures
+ *
+ */
+
+void cgroup_lock(void)
+{
+   mutex_lock(&cgroup_mutex);
+}
+
+/**
+ * cgroup_unlock - release lock on cgroup changes
+ *
+ * Undo the lock taken in a previous cgroup_lock() call.
+ */
+
+void cgroup_unlock(void)
+{
+   mutex_unlock(&cgroup_mutex);
+}
+
+/*
+ * A couple of forward declarations required, due to cyclic reference loop:
+ * cgroup_mkdir -> cgroup_create -> cgroup_populate_dir ->
+ * cgroup_add_file -> cgroup_create_file -> cgroup_dir_inode_operations
+ * -> cgroup_mkdir.
+ */
+
+static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode);
+static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry);
+static int cgroup_populate_dir(struct cgroup *cgrp);
+static struct inode_operations cgroup_dir_inode_operations;
+static struct file_operations proc_cgroupstats_operations;
+
+static struct backing_dev_info cgroup_backing_dev_info = {
+   .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
+};
+
+static struct inode *cgroup_new_inode(mode_t mode, struct super_block *sb)
+{
+   struct inode *inode = new_inode(sb);
+
+   if (inode) {
+      inode->i_mode = mode;
+      inode->i_uid = current->fsuid;
+      inode->i_gid = current->fsgid;
+      inode->i_blocks = 0;
+      inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+      inode->i_mapping->backing_dev_info = &cgroup_backing_dev_info;
+   }
+   return inode;
+}
+
+static void cgroup_diput(struct dentry *dentry, struct inode *inode)
+{
+   /* is dentry a directory ? if so, kfree() associated cgroup */
+   if (S_ISDIR(inode->i_mode)) {
+      struct cgroup *cgrp = dentry->d_fsdata;
+      BUG_ON(!(cgroup_is_removed(cgrp)));
+      /* It's possible for external users to be holding css
+       * reference counts on a cgroup; css_put() needs to
+       * be able to access the cgroup after decrementing
+       * the reference count in order to know if it needs to
+       * queue the cgroup to be handled by the release
+       * agent */
+      synchronize_rcu();
+      kfree(cgrp);
+   }
+   iput(inode);
+}
+
+static void remove_dir(struct dentry *d)
+{
+   struct dentry *parent = dget(d->d_parent);
+
+   d_delete(d);
+   simple_rmdir(parent->d_inode, d);
+   dput(parent);
+}
+
+static void cgroup_clear_directory(struct dentry *dentry)
+{
+   struct list_head *node;
+
+   BUG_ON(!mutex_is_locked(&dentry->d_inode->i_mutex));
+   spin_lock(&dcache_lock);
+   node = dentry->d_subdirs.next;
+   while (node != &dentry->d_subdirs) {
+      struct dentry *d = list_entry(node, struct dentry, d_u.d_child);
+      list_del_init(node);
+      if (d->d_inode) {
+         /* This should never be called on a cgroup
+          * directory with child cgroups */
+         BUG_ON(d->d_inode->i_mode & S_IFDIR);
+         d = dget_locked(d);
+         spin_unlock(&dcache_lock);
+         d_delete(d);
+         simple_unlink(dentry->d_inode, d);
+         dput(d);
+         spin_lock(&dcache_lock);
+      }
+      node = dentry->d_subdirs.next;
+   }
+   spin_unlock(&dcache_lock);
+}
+
+/*
+ * NOTE : the dentry must have been dget()'ed
+ */
+static void cgroup_d_remove_dir(struct dentry *dentry)
+{
+   cgroup_clear_directory(dentry);
+
+   spin_lock(&dcache_lock);
+   list_del_init(&dentry->d_u.d_child);
+   spin_unlock(&dcache_lock);
+   remove_dir(dentry);
+}
+
+static int rebind_subsystems(struct cgroupfs_root *root,
+               unsigned long final_bits)
+{
+   unsigned long added_bits, removed_bits;
+   struct cgroup *cgrp = &root->top_cgroup;
+   int i;
+
+   removed_bits = root->actual_subsys_bits & ~final_bits;
+   added_bits = final_bits & ~root->actual_subsys_bits;
+   /* Check that any added subsystems are currently free */
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      unsigned long long bit = 1ull << i;
+      struct cgroup_subsys *ss = subsys[i];
+      if (!(bit & added_bits))
+         continue;
+      if (ss->root != &rootnode) {
+         /* Subsystem isn't free */
+         return -EBUSY;
+      }
+   }
+
+   /* Currently we don't handle adding/removing subsystems when
+    * any child cgroups exist. This is theoretically supportable
+    * but involves complex error handling, so it's being left until
+    * later */
+   if (!list_empty(&cgrp->children))
+      return -EBUSY;
+
+   /* Process each subsystem */
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup_subsys *ss = subsys[i];
+      unsigned long bit = 1UL << i;
+      if (bit & added_bits) {
+         /* We're binding this subsystem to this hierarchy */
+         BUG_ON(cgrp->subsys[i]);
+         BUG_ON(!dummytop->subsys[i]);
+         BUG_ON(dummytop->subsys[i]->cgroup != dummytop);
+         cgrp->subsys[i] = dummytop->subsys[i];
+         cgrp->subsys[i]->cgroup = cgrp;
+         list_add(&ss->sibling, &root->subsys_list);
+         rcu_assign_pointer(ss->root, root);
+         if (ss->bind)
+            ss->bind(ss, cgrp);
+
+      } else if (bit & removed_bits) {
+         /* We're removing this subsystem */
+         BUG_ON(cgrp->subsys[i] != dummytop->subsys[i]);
+         BUG_ON(cgrp->subsys[i]->cgroup != cgrp);
+         if (ss->bind)
+            ss->bind(ss, dummytop);
+         dummytop->subsys[i]->cgroup = dummytop;
+         cgrp->subsys[i] = NULL;
+         rcu_assign_pointer(subsys[i]->root, &rootnode);
+         list_del(&ss->sibling);
+      } else if (bit & final_bits) {
+         /* Subsystem state should already exist */
+         BUG_ON(!cgrp->subsys[i]);
+      } else {
+         /* Subsystem state shouldn't exist */
+         BUG_ON(cgrp->subsys[i]);
+      }
+   }
+   root->subsys_bits = root->actual_subsys_bits = final_bits;
+   synchronize_rcu();
+
+   return 0;
+}
+
+static int cgroup_show_options(struct seq_file *seq, struct vfsmount *vfs)
+{
+   struct cgroupfs_root *root = vfs->mnt_sb->s_fs_info;
+   struct cgroup_subsys *ss;
+
+   mutex_lock(&cgroup_mutex);
+   for_each_subsys(root, ss)
+      seq_printf(seq, ",%s", ss->name);
+   if (test_bit(ROOT_NOPREFIX, &root->flags))
+      seq_puts(seq, ",noprefix");
+   if (strlen(root->release_agent_path))
+      seq_printf(seq, ",release_agent=%s", root->release_agent_path);
+   mutex_unlock(&cgroup_mutex);
+   return 0;
+}
+
+struct cgroup_sb_opts {
+   unsigned long subsys_bits;
+   unsigned long flags;
+   char *release_agent;
+};
+
+/* Convert a hierarchy specifier into a bitmask of subsystems and
+ * flags. */
+static int parse_cgroupfs_options(char *data,
+                 struct cgroup_sb_opts *opts)
+{
+   char *token, *o = data ?: "all";
+
+   opts->subsys_bits = 0;
+   opts->flags = 0;
+   opts->release_agent = NULL;
+
+   while ((token = strsep(&o, ",")) != NULL) {
+      if (!*token)
+         return -EINVAL;
+      if (!strcmp(token, "all")) {
+         opts->subsys_bits = (1 << CGROUP_SUBSYS_COUNT) - 1;
+      } else if (!strcmp(token, "noprefix")) {
+         set_bit(ROOT_NOPREFIX, &opts->flags);
+      } else if (!strncmp(token, "release_agent=", 14)) {
+         /* Specifying two release agents is forbidden */
+         if (opts->release_agent)
+            return -EINVAL;
+         opts->release_agent = kzalloc(PATH_MAX, GFP_KERNEL);
+         if (!opts->release_agent)
+            return -ENOMEM;
+         strncpy(opts->release_agent, token + 14, PATH_MAX - 1);
+         opts->release_agent[PATH_MAX - 1] = 0;
+      } else {
+         struct cgroup_subsys *ss;
+         int i;
+         for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+            ss = subsys[i];
+            if (!strcmp(token, ss->name)) {
+               set_bit(i, &opts->subsys_bits);
+               break;
+            }
+         }
+         if (i == CGROUP_SUBSYS_COUNT)
+            return -ENOENT;
+      }
+   }
+
+   /* We can't have an empty hierarchy */
+   if (!opts->subsys_bits)
+      return -EINVAL;
+
+   return 0;
+}
+
+static int cgroup_remount(struct super_block *sb, int *flags, char *data)
+{
+   int ret = 0;
+   struct cgroupfs_root *root = sb->s_fs_info;
+   struct cgroup *cgrp = &root->top_cgroup;
+   struct cgroup_sb_opts opts;
+
+   mutex_lock(&cgrp->dentry->d_inode->i_mutex);
+   mutex_lock(&cgroup_mutex);
+
+   /* See what subsystems are wanted */
+   ret = parse_cgroupfs_options(data, &opts);
+   if (ret)
+      goto out_unlock;
+
+   /* Don't allow flags to change at remount */
+   if (opts.flags != root->flags) {
+      ret = -EINVAL;
+      goto out_unlock;
+   }
+
+   ret = rebind_subsystems(root, opts.subsys_bits);
+
+   /* (re)populate subsystem files */
+   if (!ret)
+      cgroup_populate_dir(cgrp);
+
+   if (opts.release_agent)
+      strcpy(root->release_agent_path, opts.release_agent);
+ out_unlock:
+   if (opts.release_agent)
+      kfree(opts.release_agent);
+   mutex_unlock(&cgroup_mutex);
+   mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
+   return ret;
+}
+
+static struct super_operations cgroup_ops = {
+   .statfs = simple_statfs,
+   .drop_inode = generic_delete_inode,
+   .show_options = cgroup_show_options,
+   .remount_fs = cgroup_remount,
+};
+
+static void init_cgroup_root(struct cgroupfs_root *root)
+{
+   struct cgroup *cgrp = &root->top_cgroup;
+   INIT_LIST_HEAD(&root->subsys_list);
+   INIT_LIST_HEAD(&root->root_list);
+   root->number_of_cgroups = 1;
+   cgrp->root = root;
+   cgrp->top_cgroup = cgrp;
+   INIT_LIST_HEAD(&cgrp->sibling);
+   INIT_LIST_HEAD(&cgrp->children);
+   INIT_LIST_HEAD(&cgrp->css_sets);
+   INIT_LIST_HEAD(&cgrp->release_list);
+}
+
+static int cgroup_test_super(struct super_block *sb, void *data)
+{
+   struct cgroupfs_root *new = data;
+   struct cgroupfs_root *root = sb->s_fs_info;
+
+   /* First check subsystems */
+   if (new->subsys_bits != root->subsys_bits)
+       return 0;
+
+   /* Next check flags */
+   if (new->flags != root->flags)
+      return 0;
+
+   return 1;
+}
+
+static int cgroup_set_super(struct super_block *sb, void *data)
+{
+   int ret;
+   struct cgroupfs_root *root = data;
+
+   ret = set_anon_super(sb, NULL);
+   if (ret)
+      return ret;
+
+   sb->s_fs_info = root;
+   root->sb = sb;
+
+   sb->s_blocksize = PAGE_CACHE_SIZE;
+   sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
+   sb->s_magic = CGROUP_SUPER_MAGIC;
+   sb->s_op = &cgroup_ops;
+
+   return 0;
+}
+
+static int cgroup_get_rootdir(struct super_block *sb)
+{
+   struct inode *inode =
+      cgroup_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR, sb);
+   struct dentry *dentry;
+
+   if (!inode)
+      return -ENOMEM;
+
+   inode->i_op = &simple_dir_inode_operations;
+   inode->i_fop = &simple_dir_operations;
+   inode->i_op = &cgroup_dir_inode_operations;
+   /* directories start off with i_nlink == 2 (for "." entry) */
+   inc_nlink(inode);
+   dentry = d_alloc_root(inode);
+   if (!dentry) {
+      iput(inode);
+      return -ENOMEM;
+   }
+   sb->s_root = dentry;
+   return 0;
+}
+
+static int cgroup_get_sb(struct file_system_type *fs_type,
+          int flags, const char *unused_dev_name,
+          void *data, struct vfsmount *mnt)
+{
+   struct cgroup_sb_opts opts;
+   int ret = 0;
+   struct super_block *sb;
+   struct cgroupfs_root *root;
+   struct list_head tmp_cg_links, *l;
+   INIT_LIST_HEAD(&tmp_cg_links);
+
+   /* First find the desired set of subsystems */
+   ret = parse_cgroupfs_options(data, &opts);
+   if (ret) {
+      if (opts.release_agent)
+         kfree(opts.release_agent);
+      return ret;
+   }
+
+   root = kzalloc(sizeof(*root), GFP_KERNEL);
+   if (!root)
+      return -ENOMEM;
+
+   init_cgroup_root(root);
+   root->subsys_bits = opts.subsys_bits;
+   root->flags = opts.flags;
+   if (opts.release_agent) {
+      strcpy(root->release_agent_path, opts.release_agent);
+      kfree(opts.release_agent);
+   }
+
+   sb = sget(fs_type, cgroup_test_super, cgroup_set_super, root);
+
+   if (IS_ERR(sb)) {
+      kfree(root);
+      return PTR_ERR(sb);
+   }
+
+   if (sb->s_fs_info != root) {
+      /* Reusing an existing superblock */
+      BUG_ON(sb->s_root == NULL);
+      kfree(root);
+      root = NULL;
+   } else {
+      /* New superblock */
+      struct cgroup *cgrp = &root->top_cgroup;
+      struct inode *inode;
+
+      BUG_ON(sb->s_root != NULL);
+
+      ret = cgroup_get_rootdir(sb);
+      if (ret)
+         goto drop_new_super;
+      inode = sb->s_root->d_inode;
+
+      mutex_lock(&inode->i_mutex);
+      mutex_lock(&cgroup_mutex);
+
+      /*
+       * We're accessing css_set_count without locking
+       * css_set_lock here, but that's OK - it can only be
+       * increased by someone holding cgroup_lock, and
+       * that's us. The worst that can happen is that we
+       * have some link structures left over
+       */
+      ret = allocate_cg_links(css_set_count, &tmp_cg_links);
+      if (ret) {
+         mutex_unlock(&cgroup_mutex);
+         mutex_unlock(&inode->i_mutex);
+         goto drop_new_super;
+      }
+
+      ret = rebind_subsystems(root, root->subsys_bits);
+      if (ret == -EBUSY) {
+         mutex_unlock(&cgroup_mutex);
+         mutex_unlock(&inode->i_mutex);
+         goto drop_new_super;
+      }
+
+      /* EBUSY should be the only error here */
+      BUG_ON(ret);
+
+      list_add(&root->root_list, &roots);
+      root_count++;
+
+      sb->s_root->d_fsdata = &root->top_cgroup;
+      root->top_cgroup.dentry = sb->s_root;
+
+      /* Link the top cgroup in this hierarchy into all
+       * the css_set objects */
+      write_lock(&css_set_lock);
+      l = &init_css_set.list;
+      do {
+         struct css_set *cg;
+         struct cg_cgroup_link *link;
+         cg = list_entry(l, struct css_set, list);
+         BUG_ON(list_empty(&tmp_cg_links));
+         link = list_entry(tmp_cg_links.next,
+                 struct cg_cgroup_link,
+                 cgrp_link_list);
+         list_del(&link->cgrp_link_list);
+         link->cg = cg;
+         list_add(&link->cgrp_link_list,
+             &root->top_cgroup.css_sets);
+         list_add(&link->cg_link_list, &cg->cg_links);
+         l = l->next;
+      } while (l != &init_css_set.list);
+      write_unlock(&css_set_lock);
+
+      free_cg_links(&tmp_cg_links);
+
+      BUG_ON(!list_empty(&cgrp->sibling));
+      BUG_ON(!list_empty(&cgrp->children));
+      BUG_ON(root->number_of_cgroups != 1);
+
+      cgroup_populate_dir(cgrp);
+      mutex_unlock(&inode->i_mutex);
+      mutex_unlock(&cgroup_mutex);
+   }
+
+   return simple_set_mnt(mnt, sb);
+
+ drop_new_super:
+   up_write(&sb->s_umount);
+   deactivate_super(sb);
+   free_cg_links(&tmp_cg_links);
+   return ret;
+}
+
+static void cgroup_kill_sb(struct super_block *sb) {
+   struct cgroupfs_root *root = sb->s_fs_info;
+   struct cgroup *cgrp = &root->top_cgroup;
+   int ret;
+
+   BUG_ON(!root);
+
+   BUG_ON(root->number_of_cgroups != 1);
+   BUG_ON(!list_empty(&cgrp->children));
+   BUG_ON(!list_empty(&cgrp->sibling));
+
+   mutex_lock(&cgroup_mutex);
+
+   /* Rebind all subsystems back to the default hierarchy */
+   ret = rebind_subsystems(root, 0);
+   /* Shouldn't be able to fail ... */
+   BUG_ON(ret);
+
+   /*
+    * Release all the links from css_sets to this hierarchy's
+    * root cgroup
+    */
+   write_lock(&css_set_lock);
+   while (!list_empty(&cgrp->css_sets)) {
+      struct cg_cgroup_link *link;
+      link = list_entry(cgrp->css_sets.next,
+              struct cg_cgroup_link, cgrp_link_list);
+      list_del(&link->cg_link_list);
+      list_del(&link->cgrp_link_list);
+      kfree(link);
+   }
+   write_unlock(&css_set_lock);
+
+   if (!list_empty(&root->root_list)) {
+      list_del(&root->root_list);
+      root_count--;
+   }
+   mutex_unlock(&cgroup_mutex);
+
+   kfree(root);
+   kill_litter_super(sb);
+}
+
+static struct file_system_type cgroup_fs_type = {
+   .name = "cgroup",
+   .get_sb = cgroup_get_sb,
+   .kill_sb = cgroup_kill_sb,
+};
+
+static inline struct cgroup *__d_cgrp(struct dentry *dentry)
+{
+   return dentry->d_fsdata;
+}
+
+static inline struct cftype *__d_cft(struct dentry *dentry)
+{
+   return dentry->d_fsdata;
+}
+
+/*
+ * Called with cgroup_mutex held.  Writes path of cgroup into buf.
+ * Returns 0 on success, -errno on error.
+ */
+int cgroup_path(const struct cgroup *cgrp, char *buf, int buflen)
+{
+   char *start;
+
+   if (cgrp == dummytop) {
+      /*
+       * Inactive subsystems have no dentry for their root
+       * cgroup
+       */
+      strcpy(buf, "/");
+      return 0;
+   }
+
+   start = buf + buflen;
+
+   *--start = '\0';
+   for (;;) {
+      int len = cgrp->dentry->d_name.len;
+      if ((start -= len) < buf)
+         return -ENAMETOOLONG;
+      memcpy(start, cgrp->dentry->d_name.name, len);
+      cgrp = cgrp->parent;
+      if (!cgrp)
+         break;
+      if (!cgrp->parent)
+         continue;
+      if (--start < buf)
+         return -ENAMETOOLONG;
+      *start = '/';
+   }
+   memmove(buf, start, buf + buflen - start);
+   return 0;
+}
+
+/*
+ * Return the first subsystem attached to a cgroup's hierarchy, and
+ * its subsystem id.
+ */
+
+static void get_first_subsys(const struct cgroup *cgrp,
+         struct cgroup_subsys_state **css, int *subsys_id)
+{
+   const struct cgroupfs_root *root = cgrp->root;
+   const struct cgroup_subsys *test_ss;
+   BUG_ON(list_empty(&root->subsys_list));
+   test_ss = list_entry(root->subsys_list.next,
+              struct cgroup_subsys, sibling);
+   if (css) {
+      *css = cgrp->subsys[test_ss->subsys_id];
+      BUG_ON(!*css);
+   }
+   if (subsys_id)
+      *subsys_id = test_ss->subsys_id;
+}
+
+/*
+ * Attach task 'tsk' to cgroup 'cgrp'
+ *
+ * Call holding cgroup_mutex.  May take task_lock of
+ * the task 'pid' during call.
+ */
+static int attach_task(struct cgroup *cgrp, struct task_struct *tsk)
+{
+   int retval = 0;
+   struct cgroup_subsys *ss;
+   struct cgroup *oldcgrp;
+   struct css_set *cg = tsk->cgroups;
+   struct css_set *newcg;
+   struct cgroupfs_root *root = cgrp->root;
+   int subsys_id;
+
+   get_first_subsys(cgrp, NULL, &subsys_id);
+
+   /* Nothing to do if the task is already in that cgroup */
+   oldcgrp = task_cgroup(tsk, subsys_id);
+   if (cgrp == oldcgrp)
+      return 0;
+
+   for_each_subsys(root, ss) {
+      if (ss->can_attach) {
+         retval = ss->can_attach(ss, cgrp, tsk);
+         if (retval) {
+            return retval;
+         }
+      }
+   }
+
+   /*
+    * Locate or allocate a new css_set for this task,
+    * based on its final set of cgroups
+    */
+   newcg = find_css_set(cg, cgrp);
+   if (!newcg) {
+      return -ENOMEM;
+   }
+
+   task_lock(tsk);
+   if (tsk->flags & PF_EXITING) {
+      task_unlock(tsk);
+      put_css_set(newcg);
+      return -ESRCH;
+   }
+   rcu_assign_pointer(tsk->cgroups, newcg);
+   task_unlock(tsk);
+
+   /* Update the css_set linked lists if we're using them */
+   write_lock(&css_set_lock);
+   if (!list_empty(&tsk->cg_list)) {
+      list_del(&tsk->cg_list);
+      list_add(&tsk->cg_list, &newcg->tasks);
+   }
+   write_unlock(&css_set_lock);
+
+   for_each_subsys(root, ss) {
+      if (ss->attach) {
+         ss->attach(ss, cgrp, oldcgrp, tsk);
+      }
+   }
+   set_bit(CGRP_RELEASABLE, &oldcgrp->flags);
+   synchronize_rcu();
+   put_css_set(cg);
+   return 0;
+}
+
+/*
+ * Attach task with pid 'pid' to cgroup 'cgrp'. Call with
+ * cgroup_mutex, may take task_lock of task
+ */
+static int attach_task_by_pid(struct cgroup *cgrp, char *pidbuf)
+{
+   pid_t pid;
+   struct task_struct *tsk;
+   int ret;
+
+   if (sscanf(pidbuf, "%d", &pid) != 1)
+      return -EIO;
+
+   if (pid) {
+      rcu_read_lock();
+      tsk = find_task_by_pid(pid);
+      if (!tsk || tsk->flags & PF_EXITING) {
+         rcu_read_unlock();
+         return -ESRCH;
+      }
+      get_task_struct(tsk);
+      rcu_read_unlock();
+
+      if ((current->euid) && (current->euid != tsk->uid)
+          && (current->euid != tsk->suid)) {
+         put_task_struct(tsk);
+         return -EACCES;
+      }
+   } else {
+      tsk = current;
+      get_task_struct(tsk);
+   }
+
+   ret = attach_task(cgrp, tsk);
+   put_task_struct(tsk);
+   return ret;
+}
+
+/* The various types of files and directories in a cgroup file system */
+
+enum cgroup_filetype {
+   FILE_ROOT,
+   FILE_DIR,
+   FILE_TASKLIST,
+   FILE_NOTIFY_ON_RELEASE,
+   FILE_RELEASABLE,
+   FILE_RELEASE_AGENT,
+};
+
+static ssize_t cgroup_write_uint(struct cgroup *cgrp, struct cftype *cft,
+             struct file *file,
+             const char __user *userbuf,
+             size_t nbytes, loff_t *unused_ppos)
+{
+   char buffer[64];
+   int retval = 0;
+   u64 val;
+   char *end;
+
+   if (!nbytes)
+      return -EINVAL;
+   if (nbytes >= sizeof(buffer))
+      return -E2BIG;
+   if (copy_from_user(buffer, userbuf, nbytes))
+      return -EFAULT;
+
+   buffer[nbytes] = 0;     /* nul-terminate */
+
+   /* strip newline if necessary */
+   if (nbytes && (buffer[nbytes-1] == '\n'))
+      buffer[nbytes-1] = 0;
+   val = simple_strtoull(buffer, &end, 0);
+   if (*end)
+      return -EINVAL;
+
+   /* Pass to subsystem */
+   retval = cft->write_uint(cgrp, cft, val);
+   if (!retval)
+      retval = nbytes;
+   return retval;
+}
+
+static ssize_t cgroup_common_file_write(struct cgroup *cgrp,
+                  struct cftype *cft,
+                  struct file *file,
+                  const char __user *userbuf,
+                  size_t nbytes, loff_t *unused_ppos)
+{
+   enum cgroup_filetype type = cft->private;
+   char *buffer;
+   int retval = 0;
+
+   if (nbytes >= PATH_MAX)
+      return -E2BIG;
+
+   /* +1 for nul-terminator */
+   buffer = kmalloc(nbytes + 1, GFP_KERNEL);
+   if (buffer == NULL)
+      return -ENOMEM;
+
+   if (copy_from_user(buffer, userbuf, nbytes)) {
+      retval = -EFAULT;
+      goto out1;
+   }
+   buffer[nbytes] = 0;   /* nul-terminate */
+
+   mutex_lock(&cgroup_mutex);
+
+   if (cgroup_is_removed(cgrp)) {
+      retval = -ENODEV;
+      goto out2;
+   }
+
+   switch (type) {
+   case FILE_TASKLIST:
+      retval = attach_task_by_pid(cgrp, buffer);
+      break;
+   case FILE_NOTIFY_ON_RELEASE:
+      clear_bit(CGRP_RELEASABLE, &cgrp->flags);
+      if (simple_strtoul(buffer, NULL, 10) != 0)
+         set_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+      else
+         clear_bit(CGRP_NOTIFY_ON_RELEASE, &cgrp->flags);
+      break;
+   case FILE_RELEASE_AGENT:
+   {
+      struct cgroupfs_root *root = cgrp->root;
+      /* Strip trailing newline */
+      if (nbytes && (buffer[nbytes-1] == '\n')) {
+         buffer[nbytes-1] = 0;
+      }
+      if (nbytes < sizeof(root->release_agent_path)) {
+         /* We never write anything other than '\0'
+          * into the last char of release_agent_path,
+          * so it always remains a NUL-terminated
+          * string */
+         strncpy(root->release_agent_path, buffer, nbytes);
+         root->release_agent_path[nbytes] = 0;
+      } else {
+         retval = -ENOSPC;
+      }
+      break;
+   }
+   default:
+      retval = -EINVAL;
+      goto out2;
+   }
+
+   if (retval == 0)
+      retval = nbytes;
+out2:
+   mutex_unlock(&cgroup_mutex);
+out1:
+   kfree(buffer);
+   return retval;
+}
+
+static ssize_t cgroup_file_write(struct file *file, const char __user *buf,
+                  size_t nbytes, loff_t *ppos)
+{
+   struct cftype *cft = __d_cft(file->f_dentry);
+   struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+
+   if (!cft)
+      return -ENODEV;
+   if (cft->write)
+      return cft->write(cgrp, cft, file, buf, nbytes, ppos);
+   if (cft->write_uint)
+      return cgroup_write_uint(cgrp, cft, file, buf, nbytes, ppos);
+   return -EINVAL;
+}
+
+static ssize_t cgroup_read_uint(struct cgroup *cgrp, struct cftype *cft,
+               struct file *file,
+               char __user *buf, size_t nbytes,
+               loff_t *ppos)
+{
+   char tmp[64];
+   u64 val = cft->read_uint(cgrp, cft);
+   int len = sprintf(tmp, "%llu\n", (unsigned long long) val);
+
+   return simple_read_from_buffer(buf, nbytes, ppos, tmp, len);
+}
+
+static ssize_t cgroup_common_file_read(struct cgroup *cgrp,
+                 struct cftype *cft,
+                 struct file *file,
+                 char __user *buf,
+                 size_t nbytes, loff_t *ppos)
+{
+   enum cgroup_filetype type = cft->private;
+   char *page;
+   ssize_t retval = 0;
+   char *s;
+
+   if (!(page = (char *)__get_free_page(GFP_KERNEL)))
+      return -ENOMEM;
+
+   s = page;
+
+   switch (type) {
+   case FILE_RELEASE_AGENT:
+   {
+      struct cgroupfs_root *root;
+      size_t n;
+      mutex_lock(&cgroup_mutex);
+      root = cgrp->root;
+      n = strnlen(root->release_agent_path,
+             sizeof(root->release_agent_path));
+      n = min(n, (size_t) PAGE_SIZE);
+      strncpy(s, root->release_agent_path, n);
+      mutex_unlock(&cgroup_mutex);
+      s += n;
+      break;
+   }
+   default:
+      retval = -EINVAL;
+      goto out;
+   }
+   *s++ = '\n';
+
+   retval = simple_read_from_buffer(buf, nbytes, ppos, page, s - page);
+out:
+   free_page((unsigned long)page);
+   return retval;
+}
+
+static ssize_t cgroup_file_read(struct file *file, char __user *buf,
+               size_t nbytes, loff_t *ppos)
+{
+   struct cftype *cft = __d_cft(file->f_dentry);
+   struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+
+   if (!cft)
+      return -ENODEV;
+
+   if (cft->read)
+      return cft->read(cgrp, cft, file, buf, nbytes, ppos);
+   if (cft->read_uint)
+      return cgroup_read_uint(cgrp, cft, file, buf, nbytes, ppos);
+   return -EINVAL;
+}
+
+static int cgroup_file_open(struct inode *inode, struct file *file)
+{
+   int err;
+   struct cftype *cft;
+
+   err = generic_file_open(inode, file);
+   if (err)
+      return err;
+
+   cft = __d_cft(file->f_dentry);
+   if (!cft)
+      return -ENODEV;
+   if (cft->open)
+      err = cft->open(inode, file);
+   else
+      err = 0;
+
+   return err;
+}
+
+static int cgroup_file_release(struct inode *inode, struct file *file)
+{
+   struct cftype *cft = __d_cft(file->f_dentry);
+   if (cft->release)
+      return cft->release(inode, file);
+   return 0;
+}
+
+/*
+ * cgroup_rename - Only allow simple rename of directories in place.
+ */
+static int cgroup_rename(struct inode *old_dir, struct dentry *old_dentry,
+             struct inode *new_dir, struct dentry *new_dentry)
+{
+   if (!S_ISDIR(old_dentry->d_inode->i_mode))
+      return -ENOTDIR;
+   if (new_dentry->d_inode)
+      return -EEXIST;
+   if (old_dir != new_dir)
+      return -EIO;
+   return simple_rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
+static struct file_operations cgroup_file_operations = {
+   .read = cgroup_file_read,
+   .write = cgroup_file_write,
+   .llseek = generic_file_llseek,
+   .open = cgroup_file_open,
+   .release = cgroup_file_release,
+};
+
+static struct inode_operations cgroup_dir_inode_operations = {
+   .lookup = simple_lookup,
+   .mkdir = cgroup_mkdir,
+   .rmdir = cgroup_rmdir,
+   .rename = cgroup_rename,
+};
+
+static int cgroup_create_file(struct dentry *dentry, int mode,
+            struct super_block *sb)
+{
+   static struct dentry_operations cgroup_dops = {
+      .d_iput = cgroup_diput,
+   };
+
+   struct inode *inode;
+
+   if (!dentry)
+      return -ENOENT;
+   if (dentry->d_inode)
+      return -EEXIST;
+
+   inode = cgroup_new_inode(mode, sb);
+   if (!inode)
+      return -ENOMEM;
+
+   if (S_ISDIR(mode)) {
+      inode->i_op = &cgroup_dir_inode_operations;
+      inode->i_fop = &simple_dir_operations;
+
+      /* start off with i_nlink == 2 (for "." entry) */
+      inc_nlink(inode);
+
+      /* start with the directory inode held, so that we can
+       * populate it without racing with another mkdir */
+      mutex_lock_nested(&inode->i_mutex, I_MUTEX_CHILD);
+   } else if (S_ISREG(mode)) {
+      inode->i_size = 0;
+      inode->i_fop = &cgroup_file_operations;
+   }
+   dentry->d_op = &cgroup_dops;
+   d_instantiate(dentry, inode);
+   dget(dentry);   /* Extra count - pin the dentry in core */
+   return 0;
+}
+
+/*
+ *   cgroup_create_dir - create a directory for an object.
+ *   cgrp:   the cgroup we create the directory for.
+ *      It must have a valid ->parent field
+ *      And we are going to fill its ->dentry field.
+ *   dentry: dentry of the new cgroup
+ *   mode:   mode to set on new directory.
+ */
+static int cgroup_create_dir(struct cgroup *cgrp, struct dentry *dentry,
+            int mode)
+{
+   struct dentry *parent;
+   int error = 0;
+
+   parent = cgrp->parent->dentry;
+   error = cgroup_create_file(dentry, S_IFDIR | mode, cgrp->root->sb);
+   if (!error) {
+      dentry->d_fsdata = cgrp;
+      inc_nlink(parent->d_inode);
+      cgrp->dentry = dentry;
+      dget(dentry);
+   }
+   dput(dentry);
+
+   return error;
+}
+
+int cgroup_add_file(struct cgroup *cgrp,
+             struct cgroup_subsys *subsys,
+             const struct cftype *cft)
+{
+   struct dentry *dir = cgrp->dentry;
+   struct dentry *dentry;
+   int error;
+
+   char name[MAX_CGROUP_TYPE_NAMELEN + MAX_CFTYPE_NAME + 2] = { 0 };
+   if (subsys && !test_bit(ROOT_NOPREFIX, &cgrp->root->flags)) {
+      strcpy(name, subsys->name);
+      strcat(name, ".");
+   }
+   strcat(name, cft->name);
+   BUG_ON(!mutex_is_locked(&dir->d_inode->i_mutex));
+   dentry = lookup_one_len(name, dir, strlen(name));
+   if (!IS_ERR(dentry)) {
+      error = cgroup_create_file(dentry, 0644 | S_IFREG,
+                  cgrp->root->sb);
+      if (!error)
+         dentry->d_fsdata = (void *)cft;
+      dput(dentry);
+   } else
+      error = PTR_ERR(dentry);
+   return error;
+}
+
+int cgroup_add_files(struct cgroup *cgrp,
+         struct cgroup_subsys *subsys,
+         const struct cftype cft[],
+         int count)
+{
+   int i, err;
+   for (i = 0; i < count; i++) {
+      err = cgroup_add_file(cgrp, subsys, &cft[i]);
+      if (err)
+         return err;
+   }
+   return 0;
+}
+
+/* Count the number of tasks in a cgroup. */
+
+int cgroup_task_count(const struct cgroup *cgrp)
+{
+   int count = 0;
+   struct list_head *l;
+
+   read_lock(&css_set_lock);
+   l = cgrp->css_sets.next;
+   while (l != &cgrp->css_sets) {
+      struct cg_cgroup_link *link =
+         list_entry(l, struct cg_cgroup_link, cgrp_link_list);
+      count += atomic_read(&link->cg->ref.refcount);
+      l = l->next;
+   }
+   read_unlock(&css_set_lock);
+   return count;
+}
+
+/*
+ * Advance a list_head iterator.  The iterator should be positioned at
+ * the start of a css_set
+ */
+static void cgroup_advance_iter(struct cgroup *cgrp,
+                 struct cgroup_iter *it)
+{
+   struct list_head *l = it->cg_link;
+   struct cg_cgroup_link *link;
+   struct css_set *cg;
+
+   /* Advance to the next non-empty css_set */
+   do {
+      l = l->next;
+      if (l == &cgrp->css_sets) {
+         it->cg_link = NULL;
+         return;
+      }
+      link = list_entry(l, struct cg_cgroup_link, cgrp_link_list);
+      cg = link->cg;
+   } while (list_empty(&cg->tasks));
+   it->cg_link = l;
+   it->task = cg->tasks.next;
+}
+
+void cgroup_iter_start(struct cgroup *cgrp, struct cgroup_iter *it)
+{
+   /*
+    * The first time anyone tries to iterate across a cgroup,
+    * we need to enable the list linking each css_set to its
+    * tasks, and fix up all existing tasks.
+    */
+   if (!use_task_css_set_links) {
+      struct task_struct *p, *g;
+      write_lock(&css_set_lock);
+      use_task_css_set_links = 1;
+       do_each_thread(g, p) {
+         task_lock(p);
+         if (list_empty(&p->cg_list))
+            list_add(&p->cg_list, &p->cgroups->tasks);
+         task_unlock(p);
+       } while_each_thread(g, p);
+      write_unlock(&css_set_lock);
+   }
+   read_lock(&css_set_lock);
+   it->cg_link = &cgrp->css_sets;
+   cgroup_advance_iter(cgrp, it);
+}
+
+struct task_struct *cgroup_iter_next(struct cgroup *cgrp,
+               struct cgroup_iter *it)
+{
+   struct task_struct *res;
+   struct list_head *l = it->task;
+
+   /* If the iterator cg is NULL, we have no tasks */
+   if (!it->cg_link)
+      return NULL;
+   res = list_entry(l, struct task_struct, cg_list);
+   /* Advance iterator to find next entry */
+   l = l->next;
+   if (l == &res->cgroups->tasks) {
+      /* We reached the end of this task list - move on to
+       * the next cg_cgroup_link */
+      cgroup_advance_iter(cgrp, it);
+   } else {
+      it->task = l;
+   }
+   return res;
+}
+
+void cgroup_iter_end(struct cgroup *cgrp, struct cgroup_iter *it)
+{
+   read_unlock(&css_set_lock);
+}
+
+/*
+ * Stuff for reading the 'tasks' file.
+ *
+ * Reading this file can return large amounts of data if a cgroup has
+ * *lots* of attached tasks. So it may need several calls to read(),
+ * but we cannot guarantee that the information we produce is correct
+ * unless we produce it entirely atomically.
+ *
+ * Upon tasks file open(), a struct ctr_struct is allocated, that
+ * will have a pointer to an array (also allocated here).  The struct
+ * ctr_struct * is stored in file->private_data.  Its resources will
+ * be freed by release() when the file is closed.  The array is used
+ * to sprintf the PIDs and then used by read().
+ */
+struct ctr_struct {
+   char *buf;
+   int bufsz;
+};
+
+/*
+ * Load into 'pidarray' up to 'npids' of the tasks using cgroup
+ * 'cgrp'.  Return actual number of pids loaded.  No need to
+ * task_lock(p) when reading out p->cgroup, since we're in an RCU
+ * read section, so the css_set can't go away, and is
+ * immutable after creation.
+ */
+static int pid_array_load(pid_t *pidarray, int npids, struct cgroup *cgrp)
+{
+   int n = 0;
+   struct cgroup_iter it;
+   struct task_struct *tsk;
+   cgroup_iter_start(cgrp, &it);
+   while ((tsk = cgroup_iter_next(cgrp, &it))) {
+      if (unlikely(n == npids))
+         break;
+      pidarray[n++] = task_pid_nr(tsk);
+   }
+   cgroup_iter_end(cgrp, &it);
+   return n;
+}
+
+/**
+ * Build and fill cgroupstats so that taskstats can export it to user
+ * space.
+ *
+ * @stats: cgroupstats to fill information into
+ * @dentry: A dentry entry belonging to the cgroup for which stats have
+ * been requested.
+ */
+int cgroupstats_build(struct cgroupstats *stats, struct dentry *dentry)
+{
+   int ret = -EINVAL;
+   struct cgroup *cgrp;
+   struct cgroup_iter it;
+   struct task_struct *tsk;
+   /*
+    * Validate dentry by checking the superblock operations
+    */
+   if (dentry->d_sb->s_op != &cgroup_ops)
+       goto err;
+
+   ret = 0;
+   cgrp = dentry->d_fsdata;
+   rcu_read_lock();
+
+   cgroup_iter_start(cgrp, &it);
+   while ((tsk = cgroup_iter_next(cgrp, &it))) {
+      switch (tsk->state) {
+      case TASK_RUNNING:
+         stats->nr_running++;
+         break;
+      case TASK_INTERRUPTIBLE:
+         stats->nr_sleeping++;
+         break;
+      case TASK_UNINTERRUPTIBLE:
+         stats->nr_uninterruptible++;
+         break;
+      case TASK_STOPPED:
+         stats->nr_stopped++;
+         break;
+      default:
+         if (delayacct_is_task_waiting_on_io(tsk))
+            stats->nr_io_wait++;
+         break;
+      }
+   }
+   cgroup_iter_end(cgrp, &it);
+
+   rcu_read_unlock();
+err:
+   return ret;
+}
+
+static int cmppid(const void *a, const void *b)
+{
+   return *(pid_t *)a - *(pid_t *)b;
+}
+
+/*
+ * Convert array 'a' of 'npids' pid_t's to a string of newline separated
+ * decimal pids in 'buf'.  Don't write more than 'sz' chars, but return
+ * count 'cnt' of how many chars would be written if buf were large enough.
+ */
+static int pid_array_to_buf(char *buf, int sz, pid_t *a, int npids)
+{
+   int cnt = 0;
+   int i;
+
+   for (i = 0; i < npids; i++)
+      cnt += snprintf(buf + cnt, max(sz - cnt, 0), "%d\n", a[i]);
+   return cnt;
+}
+
+/*
+ * Handle an open on 'tasks' file.  Prepare a buffer listing the
+ * process id's of tasks currently attached to the cgroup being opened.
+ *
+ * Does not require any specific cgroup mutexes, and does not take any.
+ */
+static int cgroup_tasks_open(struct inode *unused, struct file *file)
+{
+   struct cgroup *cgrp = __d_cgrp(file->f_dentry->d_parent);
+   struct ctr_struct *ctr;
+   pid_t *pidarray;
+   int npids;
+   char c;
+
+   if (!(file->f_mode & FMODE_READ))
+      return 0;
+
+   ctr = kmalloc(sizeof(*ctr), GFP_KERNEL);
+   if (!ctr)
+      goto err0;
+
+   /*
+    * If cgroup gets more users after we read count, we won't have
+    * enough space - tough.  This race is indistinguishable to the
+    * caller from the case that the additional cgroup users didn't
+    * show up until sometime later on.
+    */
+   npids = cgroup_task_count(cgrp);
+   if (npids) {
+      pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
+      if (!pidarray)
+         goto err1;
+
+      npids = pid_array_load(pidarray, npids, cgrp);
+      sort(pidarray, npids, sizeof(pid_t), cmppid, NULL);
+
+      /* Call pid_array_to_buf() twice, first just to get bufsz */
+      ctr->bufsz = pid_array_to_buf(&c, sizeof(c), pidarray, npids) + 1;
+      ctr->buf = kmalloc(ctr->bufsz, GFP_KERNEL);
+      if (!ctr->buf)
+         goto err2;
+      ctr->bufsz = pid_array_to_buf(ctr->buf, ctr->bufsz, pidarray, npids);
+
+      kfree(pidarray);
+   } else {
+      ctr->buf = 0;
+      ctr->bufsz = 0;
+   }
+   file->private_data = ctr;
+   return 0;
+
+err2:
+   kfree(pidarray);
+err1:
+   kfree(ctr);
+err0:
+   return -ENOMEM;
+}
+
+static ssize_t cgroup_tasks_read(struct cgroup *cgrp,
+                struct cftype *cft,
+                struct file *file, char __user *buf,
+                size_t nbytes, loff_t *ppos)
+{
+   struct ctr_struct *ctr = file->private_data;
+
+   return simple_read_from_buffer(buf, nbytes, ppos, ctr->buf, ctr->bufsz);
+}
+
+static int cgroup_tasks_release(struct inode *unused_inode,
+               struct file *file)
+{
+   struct ctr_struct *ctr;
+
+   if (file->f_mode & FMODE_READ) {
+      ctr = file->private_data;
+      kfree(ctr->buf);
+      kfree(ctr);
+   }
+   return 0;
+}
+
+static u64 cgroup_read_notify_on_release(struct cgroup *cgrp,
+                   struct cftype *cft)
+{
+   return notify_on_release(cgrp);
+}
+
+static u64 cgroup_read_releasable(struct cgroup *cgrp, struct cftype *cft)
+{
+   return test_bit(CGRP_RELEASABLE, &cgrp->flags);
+}
+
+/*
+ * for the common functions, 'private' gives the type of file
+ */
+static struct cftype files[] = {
+   {
+      .name = "tasks",
+      .open = cgroup_tasks_open,
+      .read = cgroup_tasks_read,
+      .write = cgroup_common_file_write,
+      .release = cgroup_tasks_release,
+      .private = FILE_TASKLIST,
+   },
+
+   {
+      .name = "notify_on_release",
+      .read_uint = cgroup_read_notify_on_release,
+      .write = cgroup_common_file_write,
+      .private = FILE_NOTIFY_ON_RELEASE,
+   },
+
+   {
+      .name = "releasable",
+      .read_uint = cgroup_read_releasable,
+      .private = FILE_RELEASABLE,
+   }
+};
+
+static struct cftype cft_release_agent = {
+   .name = "release_agent",
+   .read = cgroup_common_file_read,
+   .write = cgroup_common_file_write,
+   .private = FILE_RELEASE_AGENT,
+};
+
+static int cgroup_populate_dir(struct cgroup *cgrp)
+{
+   int err;
+   struct cgroup_subsys *ss;
+
+   /* First clear out any existing files */
+   cgroup_clear_directory(cgrp->dentry);
+
+   err = cgroup_add_files(cgrp, NULL, files, ARRAY_SIZE(files));
+   if (err < 0)
+      return err;
+
+   if (cgrp == cgrp->top_cgroup) {
+      if ((err = cgroup_add_file(cgrp, NULL, &cft_release_agent)) < 0)
+         return err;
+   }
+
+   for_each_subsys(cgrp->root, ss) {
+      if (ss->populate && (err = ss->populate(ss, cgrp)) < 0)
+         return err;
+   }
+
+   return 0;
+}
+
+static void init_cgroup_css(struct cgroup_subsys_state *css,
+                struct cgroup_subsys *ss,
+                struct cgroup *cgrp)
+{
+   css->cgroup = cgrp;
+   atomic_set(&css->refcnt, 0);
+   css->flags = 0;
+   if (cgrp == dummytop)
+      set_bit(CSS_ROOT, &css->flags);
+   BUG_ON(cgrp->subsys[ss->subsys_id]);
+   cgrp->subsys[ss->subsys_id] = css;
+}
+
+/*
+ *   cgroup_create - create a cgroup
+ *   parent:   cgroup that will be parent of the new cgroup.
+ *   name:      name of the new cgroup. Will be strcpy'ed.
+ *   mode:      mode to set on new inode
+ *
+ *   Must be called with the mutex on the parent inode held
+ */
+
+static long cgroup_create(struct cgroup *parent, struct dentry *dentry,
+              int mode)
+{
+   struct cgroup *cgrp;
+   struct cgroupfs_root *root = parent->root;
+   int err = 0;
+   struct cgroup_subsys *ss;
+   struct super_block *sb = root->sb;
+
+   cgrp = kzalloc(sizeof(*cgrp), GFP_KERNEL);
+   if (!cgrp)
+      return -ENOMEM;
+
+   /* Grab a reference on the superblock so the hierarchy doesn't
+    * get deleted on unmount if there are child cgroups.  This
+    * can be done outside cgroup_mutex, since the sb can't
+    * disappear while someone has an open control file on the
+    * fs */
+   atomic_inc(&sb->s_active);
+
+   mutex_lock(&cgroup_mutex);
+
+   cgrp->flags = 0;
+   INIT_LIST_HEAD(&cgrp->sibling);
+   INIT_LIST_HEAD(&cgrp->children);
+   INIT_LIST_HEAD(&cgrp->css_sets);
+   INIT_LIST_HEAD(&cgrp->release_list);
+
+   cgrp->parent = parent;
+   cgrp->root = parent->root;
+   cgrp->top_cgroup = parent->top_cgroup;
+
+   for_each_subsys(root, ss) {
+      struct cgroup_subsys_state *css = ss->create(ss, cgrp);
+      if (IS_ERR(css)) {
+         err = PTR_ERR(css);
+         goto err_destroy;
+      }
+      init_cgroup_css(css, ss, cgrp);
+   }
+
+   list_add(&cgrp->sibling, &cgrp->parent->children);
+   root->number_of_cgroups++;
+
+   err = cgroup_create_dir(cgrp, dentry, mode);
+   if (err < 0)
+      goto err_remove;
+
+   /* The cgroup directory was pre-locked for us */
+   BUG_ON(!mutex_is_locked(&cgrp->dentry->d_inode->i_mutex));
+
+   err = cgroup_populate_dir(cgrp);
+   /* If err < 0, we have a half-filled directory - oh well ;) */
+
+   mutex_unlock(&cgroup_mutex);
+   mutex_unlock(&cgrp->dentry->d_inode->i_mutex);
+
+   return 0;
+
+ err_remove:
+
+   list_del(&cgrp->sibling);
+   root->number_of_cgroups--;
+
+ err_destroy:
+
+   for_each_subsys(root, ss) {
+      if (cgrp->subsys[ss->subsys_id])
+         ss->destroy(ss, cgrp);
+   }
+
+   mutex_unlock(&cgroup_mutex);
+
+   /* Release the reference count that we took on the superblock */
+   deactivate_super(sb);
+
+   kfree(cgrp);
+   return err;
+}
+
+static int cgroup_mkdir(struct inode *dir, struct dentry *dentry, int mode)
+{
+   struct cgroup *c_parent = dentry->d_parent->d_fsdata;
+
+   /* the vfs holds inode->i_mutex already */
+   return cgroup_create(c_parent, dentry, mode | S_IFDIR);
+}
+
+static inline int cgroup_has_css_refs(struct cgroup *cgrp)
+{
+   /* Check the reference count on each subsystem. Since we
+    * already established that there are no tasks in the
+    * cgroup, if the css refcount is also 0, then there should
+    * be no outstanding references, so the subsystem is safe to
+    * destroy. We scan across all subsystems rather than using
+    * the per-hierarchy linked list of mounted subsystems since
+    * we can be called via check_for_release() with no
+    * synchronization other than RCU, and the subsystem linked
+    * list isn't RCU-safe */
+   int i;
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup_subsys *ss = subsys[i];
+      struct cgroup_subsys_state *css;
+      /* Skip subsystems not in this hierarchy */
+      if (ss->root != cgrp->root)
+         continue;
+      css = cgrp->subsys[ss->subsys_id];
+      /* When called from check_for_release() it's possible
+       * that by this point the cgroup has been removed
+       * and the css deleted. But a false-positive doesn't
+       * matter, since it can only happen if the cgroup
+       * has been deleted and hence no longer needs the
+       * release agent to be called anyway. */
+      if (css && atomic_read(&css->refcnt)) {
+         return 1;
+      }
+   }
+   return 0;
+}
+
+static int cgroup_rmdir(struct inode *unused_dir, struct dentry *dentry)
+{
+   struct cgroup *cgrp = dentry->d_fsdata;
+   struct dentry *d;
+   struct cgroup *parent;
+   struct cgroup_subsys *ss;
+   struct super_block *sb;
+   struct cgroupfs_root *root;
+
+   /* the vfs holds both inode->i_mutex already */
+
+   mutex_lock(&cgroup_mutex);
+   if (atomic_read(&cgrp->count) != 0) {
+      mutex_unlock(&cgroup_mutex);
+      return -EBUSY;
+   }
+   if (!list_empty(&cgrp->children)) {
+      mutex_unlock(&cgroup_mutex);
+      return -EBUSY;
+   }
+
+   parent = cgrp->parent;
+   root = cgrp->root;
+   sb = root->sb;
+
+   if (cgroup_has_css_refs(cgrp)) {
+      mutex_unlock(&cgroup_mutex);
+      return -EBUSY;
+   }
+
+   for_each_subsys(root, ss) {
+      if (cgrp->subsys[ss->subsys_id])
+         ss->destroy(ss, cgrp);
+   }
+
+   spin_lock(&release_list_lock);
+   set_bit(CGRP_REMOVED, &cgrp->flags);
+   if (!list_empty(&cgrp->release_list))
+      list_del(&cgrp->release_list);
+   spin_unlock(&release_list_lock);
+   /* delete my sibling from parent->children */
+   list_del(&cgrp->sibling);
+   spin_lock(&cgrp->dentry->d_lock);
+   d = dget(cgrp->dentry);
+   cgrp->dentry = NULL;
+   spin_unlock(&d->d_lock);
+
+   cgroup_d_remove_dir(d);
+   dput(d);
+   root->number_of_cgroups--;
+
+   set_bit(CGRP_RELEASABLE, &parent->flags);
+   check_for_release(parent);
+
+   mutex_unlock(&cgroup_mutex);
+   /* Drop the active superblock reference that we took when we
+    * created the cgroup */
+   deactivate_super(sb);
+   return 0;
+}
+
+static void cgroup_init_subsys(struct cgroup_subsys *ss)
+{
+   struct cgroup_subsys_state *css;
+   struct list_head *l;
+
+   printk(KERN_INFO "Initializing cgroup subsys %s\n", ss->name);
+
+   /* Create the top cgroup state for this subsystem */
+   ss->root = &rootnode;
+   css = ss->create(ss, dummytop);
+   /* We don't handle early failures gracefully */
+   BUG_ON(IS_ERR(css));
+   init_cgroup_css(css, ss, dummytop);
+
+   /* Update all cgroup groups to contain a subsys
+    * pointer to this state - since the subsystem is
+    * newly registered, all tasks and hence all cgroup
+    * groups are in the subsystem's top cgroup. */
+   write_lock(&css_set_lock);
+   l = &init_css_set.list;
+   do {
+      struct css_set *cg =
+         list_entry(l, struct css_set, list);
+      cg->subsys[ss->subsys_id] = dummytop->subsys[ss->subsys_id];
+      l = l->next;
+   } while (l != &init_css_set.list);
+   write_unlock(&css_set_lock);
+
+    /* If this subsystem requested that it be notified with fork
+     * events, we should send it one now for every process in the
+     * system */
+   if (ss->fork) {
+      struct task_struct *g, *p;
+
+      read_lock(&tasklist_lock);
+      do_each_thread(g, p) {
+         ss->fork(ss, p);
+      } while_each_thread(g, p);
+      read_unlock(&tasklist_lock);
+   }
+
+   need_forkexit_callback |= ss->fork || ss->exit;
+
+   ss->active = 1;
+}
+
+/**
+ * cgroup_init_early - initialize cgroups at system boot, and
+ * initialize any subsystems that request early init.
+ */
+int __init cgroup_init_early(void)
+{
+   int i;
+   kref_init(&init_css_set.ref);
+   kref_get(&init_css_set.ref);
+   INIT_LIST_HEAD(&init_css_set.list);
+   INIT_LIST_HEAD(&init_css_set.cg_links);
+   INIT_LIST_HEAD(&init_css_set.tasks);
+   css_set_count = 1;
+   init_cgroup_root(&rootnode);
+   list_add(&rootnode.root_list, &roots);
+   root_count = 1;
+   init_task.cgroups = &init_css_set;
+
+   init_css_set_link.cg = &init_css_set;
+   list_add(&init_css_set_link.cgrp_link_list,
+       &rootnode.top_cgroup.css_sets);
+   list_add(&init_css_set_link.cg_link_list,
+       &init_css_set.cg_links);
+
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup_subsys *ss = subsys[i];
+
+      BUG_ON(!ss->name);
+      BUG_ON(strlen(ss->name) > MAX_CGROUP_TYPE_NAMELEN);
+      BUG_ON(!ss->create);
+      BUG_ON(!ss->destroy);
+      if (ss->subsys_id != i) {
+         printk(KERN_ERR "cgroup: Subsys %s id == %d\n",
+                ss->name, ss->subsys_id);
+         BUG();
+      }
+
+      if (ss->early_init)
+         cgroup_init_subsys(ss);
+   }
+   return 0;
+}
+
+/**
+ * cgroup_init - register cgroup filesystem and /proc file, and
+ * initialize any subsystems that didn't request early init.
+ */
+int __init cgroup_init(void)
+{
+   int err;
+   int i;
+   struct proc_dir_entry *entry;
+
+   err = bdi_init(&cgroup_backing_dev_info);
+   if (err)
+      return err;
+
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup_subsys *ss = subsys[i];
+      if (!ss->early_init)
+         cgroup_init_subsys(ss);
+   }
+
+   err = register_filesystem(&cgroup_fs_type);
+   if (err < 0)
+      goto out;
+
+   entry = create_proc_entry("cgroups", 0, NULL);
+   if (entry)
+      entry->proc_fops = &proc_cgroupstats_operations;
+
+out:
+   if (err)
+      bdi_destroy(&cgroup_backing_dev_info);
+
+   return err;
+}
+
+/*
+ * proc_cgroup_show()
+ *  - Print task's cgroup paths into seq_file, one line for each hierarchy
+ *  - Used for /proc/<pid>/cgroup.
+ *  - No need to task_lock(tsk) on this tsk->cgroup reference, as it
+ *    doesn't really matter if tsk->cgroup changes after we read it,
+ *    and we take cgroup_mutex, keeping attach_task() from changing it
+ *    anyway.  No need to check that tsk->cgroup != NULL, thanks to
+ *    the_top_cgroup_hack in cgroup_exit(), which sets an exiting tasks
+ *    cgroup to top_cgroup.
+ */
+
+/* TODO: Use a proper seq_file iterator */
+static int proc_cgroup_show(struct seq_file *m, void *v)
+{
+   struct pid *pid;
+   struct task_struct *tsk;
+   char *buf;
+   int retval;
+   struct cgroupfs_root *root;
+
+   retval = -ENOMEM;
+   buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+   if (!buf)
+      goto out;
+
+   retval = -ESRCH;
+   pid = m->private;
+   tsk = get_pid_task(pid, PIDTYPE_PID);
+   if (!tsk)
+      goto out_free;
+
+   retval = 0;
+
+   mutex_lock(&cgroup_mutex);
+
+   for_each_root(root) {
+      struct cgroup_subsys *ss;
+      struct cgroup *cgrp;
+      int subsys_id;
+      int count = 0;
+
+      /* Skip this hierarchy if it has no active subsystems */
+      if (!root->actual_subsys_bits)
+         continue;
+      for_each_subsys(root, ss)
+         seq_printf(m, "%s%s", count++ ? "," : "", ss->name);
+      seq_putc(m, ':');
+      get_first_subsys(&root->top_cgroup, NULL, &subsys_id);
+      cgrp = task_cgroup(tsk, subsys_id);
+      retval = cgroup_path(cgrp, buf, PAGE_SIZE);
+      if (retval < 0)
+         goto out_unlock;
+      seq_puts(m, buf);
+      seq_putc(m, '\n');
+   }
+
+out_unlock:
+   mutex_unlock(&cgroup_mutex);
+   put_task_struct(tsk);
+out_free:
+   kfree(buf);
+out:
+   return retval;
+}
+
+static int cgroup_open(struct inode *inode, struct file *file)
+{
+   struct pid *pid = PROC_I(inode)->pid;
+   return single_open(file, proc_cgroup_show, pid);
+}
+
+struct file_operations proc_cgroup_operations = {
+   .open      = cgroup_open,
+   .read      = seq_read,
+   .llseek      = seq_lseek,
+   .release   = single_release,
+};
+
+/* Display information about each subsystem and each hierarchy */
+static int proc_cgroupstats_show(struct seq_file *m, void *v)
+{
+   int i;
+
+   seq_puts(m, "#subsys_name\thierarchy\tnum_cgroups\n");
+   mutex_lock(&cgroup_mutex);
+   for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+      struct cgroup_subsys *ss = subsys[i];
+      seq_printf(m, "%s\t%lu\t%d\n",
+            ss->name, ss->root->subsys_bits,
+            ss->root->number_of_cgroups);
+   }
+   mutex_unlock(&cgroup_mutex);
+   return 0;
+}
+
+static int cgroupstats_open(struct inode *inode, struct file *file)
+{
+   return single_open(file, proc_cgroupstats_show, 0);
+}
+
+static struct file_operations proc_cgroupstats_operations = {
+   .open = cgroupstats_open,
+   .read = seq_read,
+   .llseek = seq_lseek,
+   .release = single_release,
+};
+
+/**
+ * cgroup_fork - attach newly forked task to its parents cgroup.
+ * @tsk: pointer to task_struct of forking parent process.
+ *
+ * Description: A task inherits its parent's cgroup at fork().
+ *
+ * A pointer to the shared css_set was automatically copied in
+ * fork.c by dup_task_struct().  However, we ignore that copy, since
+ * it was not made under the protection of RCU or cgroup_mutex, so
+ * might no longer be a valid cgroup pointer.  attach_task() might
+ * have already changed current->cgroups, allowing the previously
+ * referenced cgroup group to be removed and freed.
+ *
+ * At the point that cgroup_fork() is called, 'current' is the parent
+ * task, and the passed argument 'child' points to the child task.
+ */
+void cgroup_fork(struct task_struct *child)
+{
+   task_lock(current);
+   child->cgroups = current->cgroups;
+   get_css_set(child->cgroups);
+   task_unlock(current);
+   INIT_LIST_HEAD(&child->cg_list);
+}
+
+/**
+ * cgroup_fork_callbacks - called on a new task very soon before
+ * adding it to the tasklist. No need to take any locks since no-one
+ * can be operating on this task
+ */
+void cgroup_fork_callbacks(struct task_struct *child)
+{
+   if (need_forkexit_callback) {
+      int i;
+      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+         struct cgroup_subsys *ss = subsys[i];
+         if (ss->fork)
+            ss->fork(ss, child);
+      }
+   }
+}
+
+/**
+ * cgroup_post_fork - called on a new task after adding it to the
+ * task list. Adds the task to the list running through its css_set
+ * if necessary. Has to be after the task is visible on the task list
+ * in case we race with the first call to cgroup_iter_start() - to
+ * guarantee that the new task ends up on its list. */
+void cgroup_post_fork(struct task_struct *child)
+{
+   if (use_task_css_set_links) {
+      write_lock(&css_set_lock);
+      if (list_empty(&child->cg_list))
+         list_add(&child->cg_list, &child->cgroups->tasks);
+      write_unlock(&css_set_lock);
+   }
+}
+/**
+ * cgroup_exit - detach cgroup from exiting task
+ * @tsk: pointer to task_struct of exiting process
+ *
+ * Description: Detach cgroup from @tsk and release it.
+ *
+ * Note that cgroups marked notify_on_release force every task in
+ * them to take the global cgroup_mutex mutex when exiting.
+ * This could impact scaling on very large systems.  Be reluctant to
+ * use notify_on_release cgroups where very high task exit scaling
+ * is required on large systems.
+ *
+ * the_top_cgroup_hack:
+ *
+ *    Set the exiting tasks cgroup to the root cgroup (top_cgroup).
+ *
+ *    We call cgroup_exit() while the task is still competent to
+ *    handle notify_on_release(), then leave the task attached to the
+ *    root cgroup in each hierarchy for the remainder of its exit.
+ *
+ *    To do this properly, we would increment the reference count on
+ *    top_cgroup, and near the very end of the kernel/exit.c do_exit()
+ *    code we would add a second cgroup function call, to drop that
+ *    reference.  This would just create an unnecessary hot spot on
+ *    the top_cgroup reference count, to no avail.
+ *
+ *    Normally, holding a reference to a cgroup without bumping its
+ *    count is unsafe.   The cgroup could go away, or someone could
+ *    attach us to a different cgroup, decrementing the count on
+ *    the first cgroup that we never incremented.  But in this case,
+ *    top_cgroup isn't going away, and either task has PF_EXITING set,
+ *    which wards off any attach_task() attempts, or task is a failed
+ *    fork, never visible to attach_task.
+ *
+ */
+void cgroup_exit(struct task_struct *tsk, int run_callbacks)
+{
+   int i;
+   struct css_set *cg;
+
+   if (run_callbacks && need_forkexit_callback) {
+      for (i = 0; i < CGROUP_SUBSYS_COUNT; i++) {
+         struct cgroup_subsys *ss = subsys[i];
+         if (ss->exit)
+            ss->exit(ss, tsk);
+      }
+   }
+
+   /*
+    * Unlink from the css_set task list if necessary.
+    * Optimistically check cg_list before taking
+    * css_set_lock
+    */
+   if (!list_empty(&tsk->cg_list)) {
+      write_lock(&css_set_lock);
+      if (!list_empty(&tsk->cg_list))
+         list_del(&tsk->cg_list);
+      write_unlock(&css_set_lock);
+   }
+
+   /* Reassign the task to the init_css_set. */
+   task_lock(tsk);
+   cg = tsk->cgroups;
+   tsk->cgroups = &init_css_set;
+   task_unlock(tsk);
+   if (cg)
+      put_css_set_taskexit(cg);
+}
+
+/**
+ * cgroup_clone - duplicate the current cgroup in the hierarchy
+ * that the given subsystem is attached to, and move this task into
+ * the new child
+ */
+int cgroup_clone(struct task_struct *tsk, struct cgroup_subsys *subsys)
+{
+   struct dentry *dentry;
+   int ret = 0;
+   char nodename[MAX_CGROUP_TYPE_NAMELEN];
+   struct cgroup *parent, *child;
+   struct inode *inode;
+   struct css_set *cg;
+   struct cgroupfs_root *root;
+   struct cgroup_subsys *ss;
+
+   /* We shouldn't be called by an unregistered subsystem */
+   BUG_ON(!subsys->active);
+
+   /* First figure out what hierarchy and cgroup we're dealing
+    * with, and pin them so we can drop cgroup_mutex */
+   mutex_lock(&cgroup_mutex);
+ again:
+   root = subsys->root;
+   if (root == &rootnode) {
+      printk(KERN_INFO
+             "Not cloning cgroup for unused subsystem %s\n",
+             subsys->name);
+      mutex_unlock(&cgroup_mutex);
+      return 0;
+   }
+   cg = tsk->cgroups;
+   parent = task_cgroup(tsk, subsys->subsys_id);
+
+   snprintf(nodename, MAX_CGROUP_TYPE_NAMELEN, "node_%d", tsk->pid);
+
+   /* Pin the hierarchy */
+   atomic_inc(&parent->root->sb->s_active);
+
+   /* Keep the cgroup alive */
+   get_css_set(cg);
+   mutex_unlock(&cgroup_mutex);
+
+   /* Now do the VFS work to create a cgroup */
+   inode = parent->dentry->d_inode;
+
+   /* Hold the parent directory mutex across this operation to
+    * stop anyone else deleting the new cgroup */
+   mutex_lock(&inode->i_mutex);
+   dentry = lookup_one_len(nodename, parent->dentry, strlen(nodename));
+   if (IS_ERR(dentry)) {
+      printk(KERN_INFO
+             "cgroup: Couldn't allocate dentry for %s: %ld\n", nodename,
+             PTR_ERR(dentry));
+      ret = PTR_ERR(dentry);
+      goto out_release;
+   }
+
+   /* Create the cgroup directory, which also creates the cgroup */
+   ret = vfs_mkdir(inode, dentry, S_IFDIR | 0755);
+   child = __d_cgrp(dentry);
+   dput(dentry);
+   if (ret) {
+      printk(KERN_INFO
+             "Failed to create cgroup %s: %d\n", nodename,
+             ret);
+      goto out_release;
+   }
+
+   if (!child) {
+      printk(KERN_INFO
+             "Couldn't find new cgroup %s\n", nodename);
+      ret = -ENOMEM;
+      goto out_release;
+   }
+
+   /* The cgroup now exists. Retake cgroup_mutex and check
+    * that we're still in the same state that we thought we
+    * were. */
+   mutex_lock(&cgroup_mutex);
+   if ((root != subsys->root) ||
+       (parent != task_cgroup(tsk, subsys->subsys_id))) {
+      /* Aargh, we raced ... */
+      mutex_unlock(&inode->i_mutex);
+      put_css_set(cg);
+
+      deactivate_super(parent->root->sb);
+      /* The cgroup is still accessible in the VFS, but
+       * we're not going to try to rmdir() it at this
+       * point. */
+      printk(KERN_INFO
+             "Race in cgroup_clone() - leaking cgroup %s\n",
+             nodename);
+      goto again;
+   }
+
+   /* do any required auto-setup */
+   for_each_subsys(root, ss) {
+      if (ss->post_clone)
+         ss->post_clone(ss, child);
+   }
+
+   /* All seems fine. Finish by moving the task into the new cgroup */
+   ret = attach_task(child, tsk);
+   mutex_unlock(&cgroup_mutex);
+
+ out_release:
+   mutex_unlock(&inode->i_mutex);
+
+   mutex_lock(&cgroup_mutex);
+   put_css_set(cg);
+   mutex_unlock(&cgroup_mutex);
+   deactivate_super(parent->root->sb);
+   return ret;
+}
+
+/*
+ * See if "cgrp" is a descendant of the current task's cgroup in
+ * the appropriate hierarchy
+ *
+ * If we are sending in dummytop, then presumably we are creating
+ * the top cgroup in the subsystem.
+ *
+ * Called only by the ns (nsproxy) cgroup.
+ */
+int cgroup_is_descendant(const struct cgroup *cgrp)
+{
+   int ret;
+   struct cgroup *target;
+   int subsys_id;
+
+   if (cgrp == dummytop)
+      return 1;
+
+   get_first_subsys(cgrp, NULL, &subsys_id);
+   target = task_cgroup(current, subsys_id);
+   while (cgrp != target && cgrp!= cgrp->top_cgroup)
+      cgrp = cgrp->parent;
+   ret = (cgrp == target);
+   return ret;
+}
+
+static void check_for_release(struct cgroup *cgrp)
+{
+   /* All of these checks rely on RCU to keep the cgroup
+    * structure alive */
+   if (cgroup_is_releasable(cgrp) && !atomic_read(&cgrp->count)
+       && list_empty(&cgrp->children) && !cgroup_has_css_refs(cgrp)) {
+      /* Control Group is currently removeable. If it's not
+       * already queued for a userspace notification, queue
+       * it now */
+      int need_schedule_work = 0;
+      spin_lock(&release_list_lock);
+      if (!cgroup_is_removed(cgrp) &&
+          list_empty(&cgrp->release_list)) {
+         list_add(&cgrp->release_list, &release_list);
+         need_schedule_work = 1;
+      }
+      spin_unlock(&release_list_lock);
+      if (need_schedule_work)
+         schedule_work(&release_agent_work);
+   }
+}
+
+void __css_put(struct cgroup_subsys_state *css)
+{
+   struct cgroup *cgrp = css->cgroup;
+   rcu_read_lock();
+   if (atomic_dec_and_test(&css->refcnt) && notify_on_release(cgrp)) {
+      set_bit(CGRP_RELEASABLE, &cgrp->flags);
+      check_for_release(cgrp);
+   }
+   rcu_read_unlock();
+}
+
+/*
+ * Notify userspace when a cgroup is released, by running the
+ * configured release agent with the name of the cgroup (path
+ * relative to the root of cgroup file system) as the argument.
+ *
+ * Most likely, this user command will try to rmdir this cgroup.
+ *
+ * This races with the possibility that some other task will be
+ * attached to this cgroup before it is removed, or that some other
+ * user task will 'mkdir' a child cgroup of this cgroup.  That's ok.
+ * The presumed 'rmdir' will fail quietly if this cgroup is no longer
+ * unused, and this cgroup will be reprieved from its death sentence,
+ * to continue to serve a useful existence.  Next time it's released,
+ * we will get notified again, if it still has 'notify_on_release' set.
+ *
+ * The final arg to call_usermodehelper() is UMH_WAIT_EXEC, which
+ * means only wait until the task is successfully execve()'d.  The
+ * separate release agent task is forked by call_usermodehelper(),
+ * then control in this thread returns here, without waiting for the
+ * release agent task.  We don't bother to wait because the caller of
+ * this routine has no use for the exit status of the release agent
+ * task, so no sense holding our caller up for that.
+ *
+ */
+
+static void cgroup_release_agent(struct work_struct *work)
+{
+   BUG_ON(work != &release_agent_work);
+   mutex_lock(&cgroup_mutex);
+   spin_lock(&release_list_lock);
+   while (!list_empty(&release_list)) {
+      char *argv[3], *envp[3];
+      int i;
+      char *pathbuf;
+      struct cgroup *cgrp = list_entry(release_list.next,
+                      struct cgroup,
+                      release_list);
+      list_del_init(&cgrp->release_list);
+      spin_unlock(&release_list_lock);
+      pathbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
+      if (!pathbuf) {
+         spin_lock(&release_list_lock);
+         continue;
+      }
+
+      if (cgroup_path(cgrp, pathbuf, PAGE_SIZE) < 0) {
+         kfree(pathbuf);
+         spin_lock(&release_list_lock);
+         continue;
+      }
+
+      i = 0;
+      argv[i++] = cgrp->root->release_agent_path;
+      argv[i++] = (char *)pathbuf;
+      argv[i] = NULL;
+
+      i = 0;
+      /* minimal command environment */
+      envp[i++] = "HOME=/";
+      envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
+      envp[i] = NULL;
+
+      /* Drop the lock while we invoke the usermode helper,
+       * since the exec could involve hitting disk and hence
+       * be a slow process */
+      mutex_unlock(&cgroup_mutex);
+      call_usermodehelper(argv[0], argv, envp, UMH_WAIT_EXEC);
+      kfree(pathbuf);
+      mutex_lock(&cgroup_mutex);
+      spin_lock(&release_list_lock);
+   }
+   spin_unlock(&release_list_lock);
+   mutex_unlock(&cgroup_mutex);
+}