[PATCH] properly stop devices before poweroff

[linux-2.6/mini2440.git] / kernel / cpuset.c

/*
 *  kernel/cpuset.c
 *
 *  Processor and Memory placement constraints for sets of tasks.
 *
 *  Copyright (C) 2003 BULL SA.
 *  Copyright (C) 2004 Silicon Graphics, Inc.
 *
 *  Portions derived from Patrick Mochel's sysfs code.
 *  sysfs is Copyright (c) 2001-3 Patrick Mochel
 *  Portions Copyright (c) 2004 Silicon Graphics, Inc.
 *
 *  2003-10-10 Written by Simon Derr <simon.derr@bull.net>
 *  2003-10-22 Updates by Stephen Hemminger.
 *  2004 May-July Rework by Paul Jackson <pj@sgi.com>
 *
 *  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/config.h>
#include <linux/cpu.h>
#include <linux/cpumask.h>
#include <linux/cpuset.h>
#include <linux/err.h>
#include <linux/errno.h>
#include <linux/file.h>
#include <linux/fs.h>
#include <linux/init.h>
#include <linux/interrupt.h>
#include <linux/kernel.h>
#include <linux/kmod.h>
#include <linux/list.h>
#include <linux/mm.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/pagemap.h>
#include <linux/proc_fs.h>
#include <linux/sched.h>
#include <linux/seq_file.h>
#include <linux/slab.h>
#include <linux/smp_lock.h>
#include <linux/spinlock.h>
#include <linux/stat.h>
#include <linux/string.h>
#include <linux/time.h>
#include <linux/backing-dev.h>
#include <linux/sort.h>

#include <asm/uaccess.h>
#include <asm/atomic.h>
#include <asm/semaphore.h>

#define CPUSET_SUPER_MAGIC              0x27e0eb

struct cpuset {
        unsigned long flags;            /* "unsigned long" so bitops work */
        cpumask_t cpus_allowed;         /* CPUs allowed to tasks in cpuset */
        nodemask_t mems_allowed;        /* Memory Nodes allowed to tasks */

        atomic_t count;                 /* count tasks using this cpuset */

        /*
         * We link our 'sibling' struct into our parents 'children'.
         * Our children link their 'sibling' into our 'children'.
         */
        struct list_head sibling;       /* my parents children */
        struct list_head children;      /* my children */

        struct cpuset *parent;          /* my parent */
        struct dentry *dentry;          /* cpuset fs entry */

        /*
         * Copy of global cpuset_mems_generation as of the most
         * recent time this cpuset changed its mems_allowed.
         */
         int mems_generation;
};

/* bits in struct cpuset flags field */
typedef enum {
        CS_CPU_EXCLUSIVE,
        CS_MEM_EXCLUSIVE,
        CS_REMOVED,
        CS_NOTIFY_ON_RELEASE
} cpuset_flagbits_t;

/* convenient tests for these bits */
static inline int is_cpu_exclusive(const struct cpuset *cs)
{
        return !!test_bit(CS_CPU_EXCLUSIVE, &cs->flags);
}

static inline int is_mem_exclusive(const struct cpuset *cs)
{
        return !!test_bit(CS_MEM_EXCLUSIVE, &cs->flags);
}

static inline int is_removed(const struct cpuset *cs)
{
        return !!test_bit(CS_REMOVED, &cs->flags);
}

static inline int notify_on_release(const struct cpuset *cs)
{
        return !!test_bit(CS_NOTIFY_ON_RELEASE, &cs->flags);
}

/*
 * Increment this atomic integer everytime any cpuset changes its
 * mems_allowed value.  Users of cpusets can track this generation
 * number, and avoid having to lock and reload mems_allowed unless
 * the cpuset they're using changes generation.
 *
 * A single, global generation is needed because attach_task() could
 * reattach a task to a different cpuset, which must not have its
 * generation numbers aliased with those of that tasks previous cpuset.
 *
 * Generations are needed for mems_allowed because one task cannot
 * modify anothers memory placement.  So we must enable every task,
 * on every visit to __alloc_pages(), to efficiently check whether
 * its current->cpuset->mems_allowed has changed, requiring an update
 * of its current->mems_allowed.
 */
static atomic_t cpuset_mems_generation = ATOMIC_INIT(1);

static struct cpuset top_cpuset = {
        .flags = ((1 << CS_CPU_EXCLUSIVE) | (1 << CS_MEM_EXCLUSIVE)),
        .cpus_allowed = CPU_MASK_ALL,
        .mems_allowed = NODE_MASK_ALL,
        .count = ATOMIC_INIT(0),
        .sibling = LIST_HEAD_INIT(top_cpuset.sibling),
        .children = LIST_HEAD_INIT(top_cpuset.children),
        .parent = NULL,
        .dentry = NULL,
        .mems_generation = 0,
};

static struct vfsmount *cpuset_mount;
static struct super_block *cpuset_sb = NULL;

/*
 * cpuset_sem should be held by anyone who is depending on the children
 * or sibling lists of any cpuset, or performing non-atomic operations
 * on the flags or *_allowed values of a cpuset, such as raising the
 * CS_REMOVED flag bit iff it is not already raised, or reading and
 * conditionally modifying the *_allowed values.  One kernel global
 * cpuset semaphore should be sufficient - these things don't change
 * that much.
 *
 * The code that modifies cpusets holds cpuset_sem across the entire
 * operation, from cpuset_common_file_write() down, single threading
 * all cpuset modifications (except for counter manipulations from
 * fork and exit) across the system.  This presumes that cpuset
 * modifications are rare - better kept simple and safe, even if slow.
 *
 * The code that reads cpusets, such as in cpuset_common_file_read()
 * and below, only holds cpuset_sem across small pieces of code, such
 * as when reading out possibly multi-word cpumasks and nodemasks, as
 * the risks are less, and the desire for performance a little greater.
 * The proc_cpuset_show() routine needs to hold cpuset_sem to insure
 * that no cs->dentry is NULL, as it walks up the cpuset tree to root.
 *
 * The hooks from fork and exit, cpuset_fork() and cpuset_exit(), don't
 * (usually) grab cpuset_sem.  These are the two most performance
 * critical pieces of code here.  The exception occurs on exit(),
 * when a task in a notify_on_release cpuset exits.  Then cpuset_sem
 * is taken, and if the cpuset count is zero, a usermode call made
 * to /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
 * A cpuset can only be deleted if both its 'count' of using tasks is
 * zero, and its list of 'children' cpusets is empty.  Since all tasks
 * in the system use _some_ cpuset, and since there is always at least
 * one task in the system (init, pid == 1), therefore, top_cpuset
 * always has either children cpusets and/or using tasks.  So no need
 * for any special hack to ensure that top_cpuset cannot be deleted.
 */

static DECLARE_MUTEX(cpuset_sem);

/*
 * A couple of forward declarations required, due to cyclic reference loop:
 *  cpuset_mkdir -> cpuset_create -> cpuset_populate_dir -> cpuset_add_file
 *  -> cpuset_create_file -> cpuset_dir_inode_operations -> cpuset_mkdir.
 */

static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode);
static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry);

static struct backing_dev_info cpuset_backing_dev_info = {
        .ra_pages = 0,          /* No readahead */
        .capabilities   = BDI_CAP_NO_ACCT_DIRTY | BDI_CAP_NO_WRITEBACK,
};

static struct inode *cpuset_new_inode(mode_t mode)
{
        struct inode *inode = new_inode(cpuset_sb);

        if (inode) {
                inode->i_mode = mode;
                inode->i_uid = current->fsuid;
                inode->i_gid = current->fsgid;
                inode->i_blksize = PAGE_CACHE_SIZE;
                inode->i_blocks = 0;
                inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
                inode->i_mapping->backing_dev_info = &cpuset_backing_dev_info;
        }
        return inode;
}

static void cpuset_diput(struct dentry *dentry, struct inode *inode)
{
        /* is dentry a directory ? if so, kfree() associated cpuset */
        if (S_ISDIR(inode->i_mode)) {
                struct cpuset *cs = dentry->d_fsdata;
                BUG_ON(!(is_removed(cs)));
                kfree(cs);
        }
        iput(inode);
}

static struct dentry_operations cpuset_dops = {
        .d_iput = cpuset_diput,
};

static struct dentry *cpuset_get_dentry(struct dentry *parent, const char *name)
{
        struct dentry *d = lookup_one_len(name, parent, strlen(name));
        if (!IS_ERR(d))
                d->d_op = &cpuset_dops;
        return d;
}

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);
}

/*
 * NOTE : the dentry must have been dget()'ed
 */
static void cpuset_d_remove_dir(struct dentry *dentry)
{
        struct list_head *node;

        spin_lock(&dcache_lock);
        node = dentry->d_subdirs.next;
        while (node != &dentry->d_subdirs) {
                struct dentry *d = list_entry(node, struct dentry, d_child);
                list_del_init(node);
                if (d->d_inode) {
                        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;
        }
        list_del_init(&dentry->d_child);
        spin_unlock(&dcache_lock);
        remove_dir(dentry);
}

static struct super_operations cpuset_ops = {
        .statfs = simple_statfs,
        .drop_inode = generic_delete_inode,
};

static int cpuset_fill_super(struct super_block *sb, void *unused_data,
                                                        int unused_silent)
{
        struct inode *inode;
        struct dentry *root;

        sb->s_blocksize = PAGE_CACHE_SIZE;
        sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
        sb->s_magic = CPUSET_SUPER_MAGIC;
        sb->s_op = &cpuset_ops;
        cpuset_sb = sb;

        inode = cpuset_new_inode(S_IFDIR | S_IRUGO | S_IXUGO | S_IWUSR);
        if (inode) {
                inode->i_op = &simple_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;
                /* directories start off with i_nlink == 2 (for "." entry) */
                inode->i_nlink++;
        } else {
                return -ENOMEM;
        }

        root = d_alloc_root(inode);
        if (!root) {
                iput(inode);
                return -ENOMEM;
        }
        sb->s_root = root;
        return 0;
}

static struct super_block *cpuset_get_sb(struct file_system_type *fs_type,
                                        int flags, const char *unused_dev_name,
                                        void *data)
{
        return get_sb_single(fs_type, flags, data, cpuset_fill_super);
}

static struct file_system_type cpuset_fs_type = {
        .name = "cpuset",
        .get_sb = cpuset_get_sb,
        .kill_sb = kill_litter_super,
};

/* struct cftype:
 *
 * The files in the cpuset filesystem mostly have a very simple read/write
 * handling, some common function will take care of it. Nevertheless some cases
 * (read tasks) are special and therefore I define this structure for every
 * kind of file.
 *
 *
 * When reading/writing to a file:
 *      - the cpuset to use in file->f_dentry->d_parent->d_fsdata
 *      - the 'cftype' of the file is file->f_dentry->d_fsdata
 */

struct cftype {
        char *name;
        int private;
        int (*open) (struct inode *inode, struct file *file);
        ssize_t (*read) (struct file *file, char __user *buf, size_t nbytes,
                                                        loff_t *ppos);
        int (*write) (struct file *file, const char __user *buf, size_t nbytes,
                                                        loff_t *ppos);
        int (*release) (struct inode *inode, struct file *file);
};

static inline struct cpuset *__d_cs(struct dentry *dentry)
{
        return dentry->d_fsdata;
}

static inline struct cftype *__d_cft(struct dentry *dentry)
{
        return dentry->d_fsdata;
}

/*
 * Call with cpuset_sem held.  Writes path of cpuset into buf.
 * Returns 0 on success, -errno on error.
 */

static int cpuset_path(const struct cpuset *cs, char *buf, int buflen)
{
        char *start;

        start = buf + buflen;

        *--start = '\0';
        for (;;) {
                int len = cs->dentry->d_name.len;
                if ((start -= len) < buf)
                        return -ENAMETOOLONG;
                memcpy(start, cs->dentry->d_name.name, len);
                cs = cs->parent;
                if (!cs)
                        break;
                if (!cs->parent)
                        continue;
                if (--start < buf)
                        return -ENAMETOOLONG;
                *start = '/';
        }
        memmove(buf, start, buf + buflen - start);
        return 0;
}

/*
 * Notify userspace when a cpuset is released, by running
 * /sbin/cpuset_release_agent with the name of the cpuset (path
 * relative to the root of cpuset file system) as the argument.
 *
 * Most likely, this user command will try to rmdir this cpuset.
 *
 * This races with the possibility that some other task will be
 * attached to this cpuset before it is removed, or that some other
 * user task will 'mkdir' a child cpuset of this cpuset.  That's ok.
 * The presumed 'rmdir' will fail quietly if this cpuset is no longer
 * unused, and this cpuset 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.
 *
 * Note final arg to call_usermodehelper() is 0 - that means
 * don't wait.  Since we are holding the global cpuset_sem here,
 * and we are asking another thread (started from keventd) to rmdir a
 * cpuset, we can't wait - or we'd deadlock with the removing thread
 * on cpuset_sem.
 */

static int cpuset_release_agent(char *cpuset_str)
{
        char *argv[3], *envp[3];
        int i;

        i = 0;
        argv[i++] = "/sbin/cpuset_release_agent";
        argv[i++] = cpuset_str;
        argv[i] = NULL;

        i = 0;
        /* minimal command environment */
        envp[i++] = "HOME=/";
        envp[i++] = "PATH=/sbin:/bin:/usr/sbin:/usr/bin";
        envp[i] = NULL;

        return call_usermodehelper(argv[0], argv, envp, 0);
}

/*
 * Either cs->count of using tasks transitioned to zero, or the
 * cs->children list of child cpusets just became empty.  If this
 * cs is notify_on_release() and now both the user count is zero and
 * the list of children is empty, send notice to user land.
 */

static void check_for_release(struct cpuset *cs)
{
        if (notify_on_release(cs) && atomic_read(&cs->count) == 0 &&
            list_empty(&cs->children)) {
                char *buf;

                buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
                if (!buf)
                        return;
                if (cpuset_path(cs, buf, PAGE_SIZE) < 0)
                        goto out;
                cpuset_release_agent(buf);
out:
                kfree(buf);
        }
}

/*
 * Return in *pmask the portion of a cpusets's cpus_allowed that
 * are online.  If none are online, walk up the cpuset hierarchy
 * until we find one that does have some online cpus.  If we get
 * all the way to the top and still haven't found any online cpus,
 * return cpu_online_map.  Or if passed a NULL cs from an exit'ing
 * task, return cpu_online_map.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of cpu_online_map.
 *
 * Call with cpuset_sem held.
 */

static void guarantee_online_cpus(const struct cpuset *cs, cpumask_t *pmask)
{
        while (cs && !cpus_intersects(cs->cpus_allowed, cpu_online_map))
                cs = cs->parent;
        if (cs)
                cpus_and(*pmask, cs->cpus_allowed, cpu_online_map);
        else
                *pmask = cpu_online_map;
        BUG_ON(!cpus_intersects(*pmask, cpu_online_map));
}

/*
 * Return in *pmask the portion of a cpusets's mems_allowed that
 * are online.  If none are online, walk up the cpuset hierarchy
 * until we find one that does have some online mems.  If we get
 * all the way to the top and still haven't found any online mems,
 * return node_online_map.
 *
 * One way or another, we guarantee to return some non-empty subset
 * of node_online_map.
 *
 * Call with cpuset_sem held.
 */

static void guarantee_online_mems(const struct cpuset *cs, nodemask_t *pmask)
{
        while (cs && !nodes_intersects(cs->mems_allowed, node_online_map))
                cs = cs->parent;
        if (cs)
                nodes_and(*pmask, cs->mems_allowed, node_online_map);
        else
                *pmask = node_online_map;
        BUG_ON(!nodes_intersects(*pmask, node_online_map));
}

/*
 * Refresh current tasks mems_allowed and mems_generation from
 * current tasks cpuset.  Call with cpuset_sem held.
 *
 * Be sure to call refresh_mems() on any cpuset operation which
 * (1) holds cpuset_sem, and (2) might possibly alloc memory.
 * Call after obtaining cpuset_sem lock, before any possible
 * allocation.  Otherwise one risks trying to allocate memory
 * while the task cpuset_mems_generation is not the same as
 * the mems_generation in its cpuset, which would deadlock on
 * cpuset_sem in cpuset_update_current_mems_allowed().
 *
 * Since we hold cpuset_sem, once refresh_mems() is called, the
 * test (current->cpuset_mems_generation != cs->mems_generation)
 * in cpuset_update_current_mems_allowed() will remain false,
 * until we drop cpuset_sem.  Anyone else who would change our
 * cpusets mems_generation needs to lock cpuset_sem first.
 */

static void refresh_mems(void)
{
        struct cpuset *cs = current->cpuset;

        if (current->cpuset_mems_generation != cs->mems_generation) {
                guarantee_online_mems(cs, &current->mems_allowed);
                current->cpuset_mems_generation = cs->mems_generation;
        }
}

/*
 * is_cpuset_subset(p, q) - Is cpuset p a subset of cpuset q?
 *
 * One cpuset is a subset of another if all its allowed CPUs and
 * Memory Nodes are a subset of the other, and its exclusive flags
 * are only set if the other's are set.
 */

static int is_cpuset_subset(const struct cpuset *p, const struct cpuset *q)
{
        return  cpus_subset(p->cpus_allowed, q->cpus_allowed) &&
                nodes_subset(p->mems_allowed, q->mems_allowed) &&
                is_cpu_exclusive(p) <= is_cpu_exclusive(q) &&
                is_mem_exclusive(p) <= is_mem_exclusive(q);
}

/*
 * validate_change() - Used to validate that any proposed cpuset change
 *                     follows the structural rules for cpusets.
 *
 * If we replaced the flag and mask values of the current cpuset
 * (cur) with those values in the trial cpuset (trial), would
 * our various subset and exclusive rules still be valid?  Presumes
 * cpuset_sem held.
 *
 * 'cur' is the address of an actual, in-use cpuset.  Operations
 * such as list traversal that depend on the actual address of the
 * cpuset in the list must use cur below, not trial.
 *
 * 'trial' is the address of bulk structure copy of cur, with
 * perhaps one or more of the fields cpus_allowed, mems_allowed,
 * or flags changed to new, trial values.
 *
 * Return 0 if valid, -errno if not.
 */

static int validate_change(const struct cpuset *cur, const struct cpuset *trial)
{
        struct cpuset *c, *par;

        /* Each of our child cpusets must be a subset of us */
        list_for_each_entry(c, &cur->children, sibling) {
                if (!is_cpuset_subset(c, trial))
                        return -EBUSY;
        }

        /* Remaining checks don't apply to root cpuset */
        if ((par = cur->parent) == NULL)
                return 0;

        /* We must be a subset of our parent cpuset */
        if (!is_cpuset_subset(trial, par))
                return -EACCES;

        /* If either I or some sibling (!= me) is exclusive, we can't overlap */
        list_for_each_entry(c, &par->children, sibling) {
                if ((is_cpu_exclusive(trial) || is_cpu_exclusive(c)) &&
                    c != cur &&
                    cpus_intersects(trial->cpus_allowed, c->cpus_allowed))
                        return -EINVAL;
                if ((is_mem_exclusive(trial) || is_mem_exclusive(c)) &&
                    c != cur &&
                    nodes_intersects(trial->mems_allowed, c->mems_allowed))
                        return -EINVAL;
        }

        return 0;
}

static int update_cpumask(struct cpuset *cs, char *buf)
{
        struct cpuset trialcs;
        int retval;

        trialcs = *cs;
        retval = cpulist_parse(buf, trialcs.cpus_allowed);
        if (retval < 0)
                return retval;
        cpus_and(trialcs.cpus_allowed, trialcs.cpus_allowed, cpu_online_map);
        if (cpus_empty(trialcs.cpus_allowed))
                return -ENOSPC;
        retval = validate_change(cs, &trialcs);
        if (retval == 0)
                cs->cpus_allowed = trialcs.cpus_allowed;
        return retval;
}

static int update_nodemask(struct cpuset *cs, char *buf)
{
        struct cpuset trialcs;
        int retval;

        trialcs = *cs;
        retval = nodelist_parse(buf, trialcs.mems_allowed);
        if (retval < 0)
                return retval;
        nodes_and(trialcs.mems_allowed, trialcs.mems_allowed, node_online_map);
        if (nodes_empty(trialcs.mems_allowed))
                return -ENOSPC;
        retval = validate_change(cs, &trialcs);
        if (retval == 0) {
                cs->mems_allowed = trialcs.mems_allowed;
                atomic_inc(&cpuset_mems_generation);
                cs->mems_generation = atomic_read(&cpuset_mems_generation);
        }
        return retval;
}

/*
 * update_flag - read a 0 or a 1 in a file and update associated flag
 * bit: the bit to update (CS_CPU_EXCLUSIVE, CS_MEM_EXCLUSIVE,
 *                                              CS_NOTIFY_ON_RELEASE)
 * cs:  the cpuset to update
 * buf: the buffer where we read the 0 or 1
 */

static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, char *buf)
{
        int turning_on;
        struct cpuset trialcs;
        int err;

        turning_on = (simple_strtoul(buf, NULL, 10) != 0);

        trialcs = *cs;
        if (turning_on)
                set_bit(bit, &trialcs.flags);
        else
                clear_bit(bit, &trialcs.flags);

        err = validate_change(cs, &trialcs);
        if (err == 0) {
                if (turning_on)
                        set_bit(bit, &cs->flags);
                else
                        clear_bit(bit, &cs->flags);
        }
        return err;
}

static int attach_task(struct cpuset *cs, char *buf)
{
        pid_t pid;
        struct task_struct *tsk;
        struct cpuset *oldcs;
        cpumask_t cpus;

        if (sscanf(buf, "%d", &pid) != 1)
                return -EIO;
        if (cpus_empty(cs->cpus_allowed) || nodes_empty(cs->mems_allowed))
                return -ENOSPC;

        if (pid) {
                read_lock(&tasklist_lock);

                tsk = find_task_by_pid(pid);
                if (!tsk) {
                        read_unlock(&tasklist_lock);
                        return -ESRCH;
                }

                get_task_struct(tsk);
                read_unlock(&tasklist_lock);

                if ((current->euid) && (current->euid != tsk->uid)
                    && (current->euid != tsk->suid)) {
                        put_task_struct(tsk);
                        return -EACCES;
                }
        } else {
                tsk = current;
                get_task_struct(tsk);
        }

        task_lock(tsk);
        oldcs = tsk->cpuset;
        if (!oldcs) {
                task_unlock(tsk);
                put_task_struct(tsk);
                return -ESRCH;
        }
        atomic_inc(&cs->count);
        tsk->cpuset = cs;
        task_unlock(tsk);

        guarantee_online_cpus(cs, &cpus);
        set_cpus_allowed(tsk, cpus);

        put_task_struct(tsk);
        if (atomic_dec_and_test(&oldcs->count))
                check_for_release(oldcs);
        return 0;
}

/* The various types of files and directories in a cpuset file system */

typedef enum {
        FILE_ROOT,
        FILE_DIR,
        FILE_CPULIST,
        FILE_MEMLIST,
        FILE_CPU_EXCLUSIVE,
        FILE_MEM_EXCLUSIVE,
        FILE_NOTIFY_ON_RELEASE,
        FILE_TASKLIST,
} cpuset_filetype_t;

static ssize_t cpuset_common_file_write(struct file *file, const char __user *userbuf,
                                        size_t nbytes, loff_t *unused_ppos)
{
        struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
        struct cftype *cft = __d_cft(file->f_dentry);
        cpuset_filetype_t type = cft->private;
        char *buffer;
        int retval = 0;

        /* Crude upper limit on largest legitimate cpulist user might write. */
        if (nbytes > 100 + 6 * NR_CPUS)
                return -E2BIG;

        /* +1 for nul-terminator */
        if ((buffer = kmalloc(nbytes + 1, GFP_KERNEL)) == 0)
                return -ENOMEM;

        if (copy_from_user(buffer, userbuf, nbytes)) {
                retval = -EFAULT;
                goto out1;
        }
        buffer[nbytes] = 0;     /* nul-terminate */

        down(&cpuset_sem);

        if (is_removed(cs)) {
                retval = -ENODEV;
                goto out2;
        }

        switch (type) {
        case FILE_CPULIST:
                retval = update_cpumask(cs, buffer);
                break;
        case FILE_MEMLIST:
                retval = update_nodemask(cs, buffer);
                break;
        case FILE_CPU_EXCLUSIVE:
                retval = update_flag(CS_CPU_EXCLUSIVE, cs, buffer);
                break;
        case FILE_MEM_EXCLUSIVE:
                retval = update_flag(CS_MEM_EXCLUSIVE, cs, buffer);
                break;
        case FILE_NOTIFY_ON_RELEASE:
                retval = update_flag(CS_NOTIFY_ON_RELEASE, cs, buffer);
                break;
        case FILE_TASKLIST:
                retval = attach_task(cs, buffer);
                break;
        default:
                retval = -EINVAL;
                goto out2;
        }

        if (retval == 0)
                retval = nbytes;
out2:
        up(&cpuset_sem);
out1:
        kfree(buffer);
        return retval;
}

static ssize_t cpuset_file_write(struct file *file, const char __user *buf,
                                                size_t nbytes, loff_t *ppos)
{
        ssize_t retval = 0;
        struct cftype *cft = __d_cft(file->f_dentry);
        if (!cft)
                return -ENODEV;

        /* special function ? */
        if (cft->write)
                retval = cft->write(file, buf, nbytes, ppos);
        else
                retval = cpuset_common_file_write(file, buf, nbytes, ppos);

        return retval;
}

/*
 * These ascii lists should be read in a single call, by using a user
 * buffer large enough to hold the entire map.  If read in smaller
 * chunks, there is no guarantee of atomicity.  Since the display format
 * used, list of ranges of sequential numbers, is variable length,
 * and since these maps can change value dynamically, one could read
 * gibberish by doing partial reads while a list was changing.
 * A single large read to a buffer that crosses a page boundary is
 * ok, because the result being copied to user land is not recomputed
 * across a page fault.
 */

static int cpuset_sprintf_cpulist(char *page, struct cpuset *cs)
{
        cpumask_t mask;

        down(&cpuset_sem);
        mask = cs->cpus_allowed;
        up(&cpuset_sem);

        return cpulist_scnprintf(page, PAGE_SIZE, mask);
}

static int cpuset_sprintf_memlist(char *page, struct cpuset *cs)
{
        nodemask_t mask;

        down(&cpuset_sem);
        mask = cs->mems_allowed;
        up(&cpuset_sem);

        return nodelist_scnprintf(page, PAGE_SIZE, mask);
}

static ssize_t cpuset_common_file_read(struct file *file, char __user *buf,
                                size_t nbytes, loff_t *ppos)
{
        struct cftype *cft = __d_cft(file->f_dentry);
        struct cpuset *cs = __d_cs(file->f_dentry->d_parent);
        cpuset_filetype_t type = cft->private;
        char *page;
        ssize_t retval = 0;
        char *s;
        char *start;
        size_t n;

        if (!(page = (char *)__get_free_page(GFP_KERNEL)))
                return -ENOMEM;

        s = page;

        switch (type) {
        case FILE_CPULIST:
                s += cpuset_sprintf_cpulist(s, cs);
                break;
        case FILE_MEMLIST:
                s += cpuset_sprintf_memlist(s, cs);
                break;
        case FILE_CPU_EXCLUSIVE:
                *s++ = is_cpu_exclusive(cs) ? '1' : '0';
                break;
        case FILE_MEM_EXCLUSIVE:
                *s++ = is_mem_exclusive(cs) ? '1' : '0';
                break;
        case FILE_NOTIFY_ON_RELEASE:
                *s++ = notify_on_release(cs) ? '1' : '0';
                break;
        default:
                retval = -EINVAL;
                goto out;
        }
        *s++ = '\n';
        *s = '\0';

        start = page + *ppos;
        n = s - start;
        retval = n - copy_to_user(buf, start, min(n, nbytes));
        *ppos += retval;
out:
        free_page((unsigned long)page);
        return retval;
}

static ssize_t cpuset_file_read(struct file *file, char __user *buf, size_t nbytes,
                                                                loff_t *ppos)
{
        ssize_t retval = 0;
        struct cftype *cft = __d_cft(file->f_dentry);
        if (!cft)
                return -ENODEV;

        /* special function ? */
        if (cft->read)
                retval = cft->read(file, buf, nbytes, ppos);
        else
                retval = cpuset_common_file_read(file, buf, nbytes, ppos);

        return retval;
}

static int cpuset_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 cpuset_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;
}

static struct file_operations cpuset_file_operations = {
        .read = cpuset_file_read,
        .write = cpuset_file_write,
        .llseek = generic_file_llseek,
        .open = cpuset_file_open,
        .release = cpuset_file_release,
};

static struct inode_operations cpuset_dir_inode_operations = {
        .lookup = simple_lookup,
        .mkdir = cpuset_mkdir,
        .rmdir = cpuset_rmdir,
};

static int cpuset_create_file(struct dentry *dentry, int mode)
{
        struct inode *inode;

        if (!dentry)
                return -ENOENT;
        if (dentry->d_inode)
                return -EEXIST;

        inode = cpuset_new_inode(mode);
        if (!inode)
                return -ENOMEM;

        if (S_ISDIR(mode)) {
                inode->i_op = &cpuset_dir_inode_operations;
                inode->i_fop = &simple_dir_operations;

                /* start off with i_nlink == 2 (for "." entry) */
                inode->i_nlink++;
        } else if (S_ISREG(mode)) {
                inode->i_size = 0;
                inode->i_fop = &cpuset_file_operations;
        }

        d_instantiate(dentry, inode);
        dget(dentry);   /* Extra count - pin the dentry in core */
        return 0;
}

/*
 *      cpuset_create_dir - create a directory for an object.
 *      cs:     the cpuset we create the directory for.
 *              It must have a valid ->parent field
 *              And we are going to fill its ->dentry field.
 *      name:   The name to give to the cpuset directory. Will be copied.
 *      mode:   mode to set on new directory.
 */

static int cpuset_create_dir(struct cpuset *cs, const char *name, int mode)
{
        struct dentry *dentry = NULL;
        struct dentry *parent;
        int error = 0;

        parent = cs->parent->dentry;
        dentry = cpuset_get_dentry(parent, name);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);
        error = cpuset_create_file(dentry, S_IFDIR | mode);
        if (!error) {
                dentry->d_fsdata = cs;
                parent->d_inode->i_nlink++;
                cs->dentry = dentry;
        }
        dput(dentry);

        return error;
}

static int cpuset_add_file(struct dentry *dir, const struct cftype *cft)
{
        struct dentry *dentry;
        int error;

        down(&dir->d_inode->i_sem);
        dentry = cpuset_get_dentry(dir, cft->name);
        if (!IS_ERR(dentry)) {
                error = cpuset_create_file(dentry, 0644 | S_IFREG);
                if (!error)
                        dentry->d_fsdata = (void *)cft;
                dput(dentry);
        } else
                error = PTR_ERR(dentry);
        up(&dir->d_inode->i_sem);
        return error;
}

/*
 * Stuff for reading the 'tasks' file.
 *
 * Reading this file can return large amounts of data if a cpuset 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().
 */

/* cpusets_tasks_read array */

struct ctr_struct {
        char *buf;
        int bufsz;
};

/*
 * Load into 'pidarray' up to 'npids' of the tasks using cpuset 'cs'.
 * Return actual number of pids loaded.
 */
static inline int pid_array_load(pid_t *pidarray, int npids, struct cpuset *cs)
{
        int n = 0;
        struct task_struct *g, *p;

        read_lock(&tasklist_lock);

        do_each_thread(g, p) {
                if (p->cpuset == cs) {
                        pidarray[n++] = p->pid;
                        if (unlikely(n == npids))
                                goto array_full;
                }
        } while_each_thread(g, p);

array_full:
        read_unlock(&tasklist_lock);
        return n;
}

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;
}

static int cpuset_tasks_open(struct inode *unused, struct file *file)
{
        struct cpuset *cs = __d_cs(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 cpuset 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 cpuset users didn't
         * show up until sometime later on.
         */
        npids = atomic_read(&cs->count);
        pidarray = kmalloc(npids * sizeof(pid_t), GFP_KERNEL);
        if (!pidarray)
                goto err1;

        npids = pid_array_load(pidarray, npids, cs);
        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);
        file->private_data = ctr;
        return 0;

err2:
        kfree(pidarray);
err1:
        kfree(ctr);
err0:
        return -ENOMEM;
}

static ssize_t cpuset_tasks_read(struct file *file, char __user *buf,
                                                size_t nbytes, loff_t *ppos)
{
        struct ctr_struct *ctr = file->private_data;

        if (*ppos + nbytes > ctr->bufsz)
                nbytes = ctr->bufsz - *ppos;
        if (copy_to_user(buf, ctr->buf + *ppos, nbytes))
                return -EFAULT;
        *ppos += nbytes;
        return nbytes;
}

static int cpuset_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;
}

/*
 * for the common functions, 'private' gives the type of file
 */

static struct cftype cft_tasks = {
        .name = "tasks",
        .open = cpuset_tasks_open,
        .read = cpuset_tasks_read,
        .release = cpuset_tasks_release,
        .private = FILE_TASKLIST,
};

static struct cftype cft_cpus = {
        .name = "cpus",
        .private = FILE_CPULIST,
};

static struct cftype cft_mems = {
        .name = "mems",
        .private = FILE_MEMLIST,
};

static struct cftype cft_cpu_exclusive = {
        .name = "cpu_exclusive",
        .private = FILE_CPU_EXCLUSIVE,
};

static struct cftype cft_mem_exclusive = {
        .name = "mem_exclusive",
        .private = FILE_MEM_EXCLUSIVE,
};

static struct cftype cft_notify_on_release = {
        .name = "notify_on_release",
        .private = FILE_NOTIFY_ON_RELEASE,
};

static int cpuset_populate_dir(struct dentry *cs_dentry)
{
        int err;

        if ((err = cpuset_add_file(cs_dentry, &cft_cpus)) < 0)
                return err;
        if ((err = cpuset_add_file(cs_dentry, &cft_mems)) < 0)
                return err;
        if ((err = cpuset_add_file(cs_dentry, &cft_cpu_exclusive)) < 0)
                return err;
        if ((err = cpuset_add_file(cs_dentry, &cft_mem_exclusive)) < 0)
                return err;
        if ((err = cpuset_add_file(cs_dentry, &cft_notify_on_release)) < 0)
                return err;
        if ((err = cpuset_add_file(cs_dentry, &cft_tasks)) < 0)
                return err;
        return 0;
}

/*
 *      cpuset_create - create a cpuset
 *      parent: cpuset that will be parent of the new cpuset.
 *      name:           name of the new cpuset. Will be strcpy'ed.
 *      mode:           mode to set on new inode
 *
 *      Must be called with the semaphore on the parent inode held
 */

static long cpuset_create(struct cpuset *parent, const char *name, int mode)
{
        struct cpuset *cs;
        int err;

        cs = kmalloc(sizeof(*cs), GFP_KERNEL);
        if (!cs)
                return -ENOMEM;

        down(&cpuset_sem);
        refresh_mems();
        cs->flags = 0;
        if (notify_on_release(parent))
                set_bit(CS_NOTIFY_ON_RELEASE, &cs->flags);
        cs->cpus_allowed = CPU_MASK_NONE;
        cs->mems_allowed = NODE_MASK_NONE;
        atomic_set(&cs->count, 0);
        INIT_LIST_HEAD(&cs->sibling);
        INIT_LIST_HEAD(&cs->children);
        atomic_inc(&cpuset_mems_generation);
        cs->mems_generation = atomic_read(&cpuset_mems_generation);

        cs->parent = parent;

        list_add(&cs->sibling, &cs->parent->children);

        err = cpuset_create_dir(cs, name, mode);
        if (err < 0)
                goto err;

        /*
         * Release cpuset_sem before cpuset_populate_dir() because it
         * will down() this new directory's i_sem and if we race with
         * another mkdir, we might deadlock.
         */
        up(&cpuset_sem);

        err = cpuset_populate_dir(cs->dentry);
        /* If err < 0, we have a half-filled directory - oh well ;) */
        return 0;
err:
        list_del(&cs->sibling);
        up(&cpuset_sem);
        kfree(cs);
        return err;
}

static int cpuset_mkdir(struct inode *dir, struct dentry *dentry, int mode)
{
        struct cpuset *c_parent = dentry->d_parent->d_fsdata;

        /* the vfs holds inode->i_sem already */
        return cpuset_create(c_parent, dentry->d_name.name, mode | S_IFDIR);
}

static int cpuset_rmdir(struct inode *unused_dir, struct dentry *dentry)
{
        struct cpuset *cs = dentry->d_fsdata;
        struct dentry *d;
        struct cpuset *parent;

        /* the vfs holds both inode->i_sem already */

        down(&cpuset_sem);
        refresh_mems();
        if (atomic_read(&cs->count) > 0) {
                up(&cpuset_sem);
                return -EBUSY;
        }
        if (!list_empty(&cs->children)) {
                up(&cpuset_sem);
                return -EBUSY;
        }
        spin_lock(&cs->dentry->d_lock);
        parent = cs->parent;
        set_bit(CS_REMOVED, &cs->flags);
        list_del(&cs->sibling); /* delete my sibling from parent->children */
        if (list_empty(&parent->children))
                check_for_release(parent);
        d = dget(cs->dentry);
        cs->dentry = NULL;
        spin_unlock(&d->d_lock);
        cpuset_d_remove_dir(d);
        dput(d);
        up(&cpuset_sem);
        return 0;
}

/**
 * cpuset_init - initialize cpusets at system boot
 *
 * Description: Initialize top_cpuset and the cpuset internal file system,
 **/

int __init cpuset_init(void)
{
        struct dentry *root;
        int err;

        top_cpuset.cpus_allowed = CPU_MASK_ALL;
        top_cpuset.mems_allowed = NODE_MASK_ALL;

        atomic_inc(&cpuset_mems_generation);
        top_cpuset.mems_generation = atomic_read(&cpuset_mems_generation);

        init_task.cpuset = &top_cpuset;

        err = register_filesystem(&cpuset_fs_type);
        if (err < 0)
                goto out;
        cpuset_mount = kern_mount(&cpuset_fs_type);
        if (IS_ERR(cpuset_mount)) {
                printk(KERN_ERR "cpuset: could not mount!\n");
                err = PTR_ERR(cpuset_mount);
                cpuset_mount = NULL;
                goto out;
        }
        root = cpuset_mount->mnt_sb->s_root;
        root->d_fsdata = &top_cpuset;
        root->d_inode->i_nlink++;
        top_cpuset.dentry = root;
        root->d_inode->i_op = &cpuset_dir_inode_operations;
        err = cpuset_populate_dir(root);
out:
        return err;
}

/**
 * cpuset_init_smp - initialize cpus_allowed
 *
 * Description: Finish top cpuset after cpu, node maps are initialized
 **/

void __init cpuset_init_smp(void)
{
        top_cpuset.cpus_allowed = cpu_online_map;
        top_cpuset.mems_allowed = node_online_map;
}

/**
 * cpuset_fork - attach newly forked task to its parents cpuset.
 * @p: pointer to task_struct of forking parent process.
 *
 * Description: By default, on fork, a task inherits its
 * parents cpuset.  The pointer to the shared cpuset is
 * automatically copied in fork.c by dup_task_struct().
 * This cpuset_fork() routine need only increment the usage
 * counter in that cpuset.
 **/

void cpuset_fork(struct task_struct *tsk)
{
        atomic_inc(&tsk->cpuset->count);
}

/**
 * cpuset_exit - detach cpuset from exiting task
 * @tsk: pointer to task_struct of exiting process
 *
 * Description: Detach cpuset from @tsk and release it.
 *
 * Note that cpusets marked notify_on_release force every task
 * in them to take the global cpuset_sem semaphore when exiting.
 * This could impact scaling on very large systems.  Be reluctant
 * to use notify_on_release cpusets where very high task exit
 * scaling is required on large systems.
 *
 * Don't even think about derefencing 'cs' after the cpuset use
 * count goes to zero, except inside a critical section guarded
 * by the cpuset_sem semaphore.  If you don't hold cpuset_sem,
 * then a zero cpuset use count is a license to any other task to
 * nuke the cpuset immediately.
 *
 **/

void cpuset_exit(struct task_struct *tsk)
{
        struct cpuset *cs;

        task_lock(tsk);
        cs = tsk->cpuset;
        tsk->cpuset = NULL;
        task_unlock(tsk);

        if (notify_on_release(cs)) {
                down(&cpuset_sem);
                if (atomic_dec_and_test(&cs->count))
                        check_for_release(cs);
                up(&cpuset_sem);
        } else {
                atomic_dec(&cs->count);
        }
}

/**
 * cpuset_cpus_allowed - return cpus_allowed mask from a tasks cpuset.
 * @tsk: pointer to task_struct from which to obtain cpuset->cpus_allowed.
 *
 * Description: Returns the cpumask_t cpus_allowed of the cpuset
 * attached to the specified @tsk.  Guaranteed to return some non-empty
 * subset of cpu_online_map, even if this means going outside the
 * tasks cpuset.
 **/

cpumask_t cpuset_cpus_allowed(const struct task_struct *tsk)
{
        cpumask_t mask;

        down(&cpuset_sem);
        task_lock((struct task_struct *)tsk);
        guarantee_online_cpus(tsk->cpuset, &mask);
        task_unlock((struct task_struct *)tsk);
        up(&cpuset_sem);

        return mask;
}

void cpuset_init_current_mems_allowed(void)
{
        current->mems_allowed = NODE_MASK_ALL;
}

/*
 * If the current tasks cpusets mems_allowed changed behind our backs,
 * update current->mems_allowed and mems_generation to the new value.
 * Do not call this routine if in_interrupt().
 */

void cpuset_update_current_mems_allowed(void)
{
        struct cpuset *cs = current->cpuset;

        if (!cs)
                return;         /* task is exiting */
        if (current->cpuset_mems_generation != cs->mems_generation) {
                down(&cpuset_sem);
                refresh_mems();
                up(&cpuset_sem);
        }
}

void cpuset_restrict_to_mems_allowed(unsigned long *nodes)
{
        bitmap_and(nodes, nodes, nodes_addr(current->mems_allowed),
                                                        MAX_NUMNODES);
}

/*
 * Are any of the nodes on zonelist zl allowed in current->mems_allowed?
 */
int cpuset_zonelist_valid_mems_allowed(struct zonelist *zl)
{
        int i;

        for (i = 0; zl->zones[i]; i++) {
                int nid = zl->zones[i]->zone_pgdat->node_id;

                if (node_isset(nid, current->mems_allowed))
                        return 1;
        }
        return 0;
}

/*
 * Is 'current' valid, and is zone z allowed in current->mems_allowed?
 */
int cpuset_zone_allowed(struct zone *z)
{
        return in_interrupt() ||
                node_isset(z->zone_pgdat->node_id, current->mems_allowed);
}

/*
 * proc_cpuset_show()
 *  - Print tasks cpuset path into seq_file.
 *  - Used for /proc/<pid>/cpuset.
 */

static int proc_cpuset_show(struct seq_file *m, void *v)
{
        struct cpuset *cs;
        struct task_struct *tsk;
        char *buf;
        int retval = 0;

        buf = kmalloc(PAGE_SIZE, GFP_KERNEL);
        if (!buf)
                return -ENOMEM;

        tsk = m->private;
        down(&cpuset_sem);
        task_lock(tsk);
        cs = tsk->cpuset;
        task_unlock(tsk);
        if (!cs) {
                retval = -EINVAL;
                goto out;
        }

        retval = cpuset_path(cs, buf, PAGE_SIZE);
        if (retval < 0)
                goto out;
        seq_puts(m, buf);
        seq_putc(m, '\n');
out:
        up(&cpuset_sem);
        kfree(buf);
        return retval;
}

static int cpuset_open(struct inode *inode, struct file *file)
{
        struct task_struct *tsk = PROC_I(inode)->task;
        return single_open(file, proc_cpuset_show, tsk);
}

struct file_operations proc_cpuset_operations = {
        .open           = cpuset_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = single_release,
};

/* Display task cpus_allowed, mems_allowed in /proc/<pid>/status file. */
char *cpuset_task_status_allowed(struct task_struct *task, char *buffer)
{
        buffer += sprintf(buffer, "Cpus_allowed:\t");
        buffer += cpumask_scnprintf(buffer, PAGE_SIZE, task->cpus_allowed);
        buffer += sprintf(buffer, "\n");
        buffer += sprintf(buffer, "Mems_allowed:\t");
        buffer += nodemask_scnprintf(buffer, PAGE_SIZE, task->mems_allowed);
        buffer += sprintf(buffer, "\n");
        return buffer;
}