Don't truncate /proc/PID/environ at 4096 characters

[linux-2.6/x86.git] / fs / proc / base.c

/*
 *  linux/fs/proc/base.c
 *
 *  Copyright (C) 1991, 1992 Linus Torvalds
 *
 *  proc base directory handling functions
 *
 *  1999, Al Viro. Rewritten. Now it covers the whole per-process part.
 *  Instead of using magical inumbers to determine the kind of object
 *  we allocate and fill in-core inodes upon lookup. They don't even
 *  go into icache. We cache the reference to task_struct upon lookup too.
 *  Eventually it should become a filesystem in its own. We don't use the
 *  rest of procfs anymore.
 *
 *
 *  Changelog:
 *  17-Jan-2005
 *  Allan Bezerra
 *  Bruna Moreira <bruna.moreira@indt.org.br>
 *  Edjard Mota <edjard.mota@indt.org.br>
 *  Ilias Biris <ilias.biris@indt.org.br>
 *  Mauricio Lin <mauricio.lin@indt.org.br>
 *
 *  Embedded Linux Lab - 10LE Instituto Nokia de Tecnologia - INdT
 *
 *  A new process specific entry (smaps) included in /proc. It shows the
 *  size of rss for each memory area. The maps entry lacks information
 *  about physical memory size (rss) for each mapped file, i.e.,
 *  rss information for executables and library files.
 *  This additional information is useful for any tools that need to know
 *  about physical memory consumption for a process specific library.
 *
 *  Changelog:
 *  21-Feb-2005
 *  Embedded Linux Lab - 10LE Instituto Nokia de Tecnologia - INdT
 *  Pud inclusion in the page table walking.
 *
 *  ChangeLog:
 *  10-Mar-2005
 *  10LE Instituto Nokia de Tecnologia - INdT:
 *  A better way to walks through the page table as suggested by Hugh Dickins.
 *
 *  Simo Piiroinen <simo.piiroinen@nokia.com>:
 *  Smaps information related to shared, private, clean and dirty pages.
 *
 *  Paul Mundt <paul.mundt@nokia.com>:
 *  Overall revision about smaps.
 */

#include <asm/uaccess.h>

#include <linux/errno.h>
#include <linux/time.h>
#include <linux/proc_fs.h>
#include <linux/stat.h>
#include <linux/init.h>
#include <linux/capability.h>
#include <linux/file.h>
#include <linux/string.h>
#include <linux/seq_file.h>
#include <linux/namei.h>
#include <linux/mnt_namespace.h>
#include <linux/mm.h>
#include <linux/rcupdate.h>
#include <linux/kallsyms.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/security.h>
#include <linux/ptrace.h>
#include <linux/cpuset.h>
#include <linux/audit.h>
#include <linux/poll.h>
#include <linux/nsproxy.h>
#include <linux/oom.h>
#include <linux/elf.h>
#include "internal.h"

/* NOTE:
 *      Implementing inode permission operations in /proc is almost
 *      certainly an error.  Permission checks need to happen during
 *      each system call not at open time.  The reason is that most of
 *      what we wish to check for permissions in /proc varies at runtime.
 *
 *      The classic example of a problem is opening file descriptors
 *      in /proc for a task before it execs a suid executable.
 */


/* Worst case buffer size needed for holding an integer. */
#define PROC_NUMBUF 13

struct pid_entry {
        char *name;
        int len;
        mode_t mode;
        const struct inode_operations *iop;
        const struct file_operations *fop;
        union proc_op op;
};

#define NOD(NAME, MODE, IOP, FOP, OP) {                 \
        .name = (NAME),                                 \
        .len  = sizeof(NAME) - 1,                       \
        .mode = MODE,                                   \
        .iop  = IOP,                                    \
        .fop  = FOP,                                    \
        .op   = OP,                                     \
}

#define DIR(NAME, MODE, OTYPE)                                                  \
        NOD(NAME, (S_IFDIR|(MODE)),                                             \
                &proc_##OTYPE##_inode_operations, &proc_##OTYPE##_operations,   \
                {} )
#define LNK(NAME, OTYPE)                                        \
        NOD(NAME, (S_IFLNK|S_IRWXUGO),                          \
                &proc_pid_link_inode_operations, NULL,          \
                { .proc_get_link = &proc_##OTYPE##_link } )
#define REG(NAME, MODE, OTYPE)                          \
        NOD(NAME, (S_IFREG|(MODE)), NULL,               \
                &proc_##OTYPE##_operations, {})
#define INF(NAME, MODE, OTYPE)                          \
        NOD(NAME, (S_IFREG|(MODE)),                     \
                NULL, &proc_info_file_operations,       \
                { .proc_read = &proc_##OTYPE } )

int maps_protect;
EXPORT_SYMBOL(maps_protect);

static struct fs_struct *get_fs_struct(struct task_struct *task)
{
        struct fs_struct *fs;
        task_lock(task);
        fs = task->fs;
        if(fs)
                atomic_inc(&fs->count);
        task_unlock(task);
        return fs;
}

static int get_nr_threads(struct task_struct *tsk)
{
        /* Must be called with the rcu_read_lock held */
        unsigned long flags;
        int count = 0;

        if (lock_task_sighand(tsk, &flags)) {
                count = atomic_read(&tsk->signal->count);
                unlock_task_sighand(tsk, &flags);
        }
        return count;
}

static int proc_cwd_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
{
        struct task_struct *task = get_proc_task(inode);
        struct fs_struct *fs = NULL;
        int result = -ENOENT;

        if (task) {
                fs = get_fs_struct(task);
                put_task_struct(task);
        }
        if (fs) {
                read_lock(&fs->lock);
                *mnt = mntget(fs->pwdmnt);
                *dentry = dget(fs->pwd);
                read_unlock(&fs->lock);
                result = 0;
                put_fs_struct(fs);
        }
        return result;
}

static int proc_root_link(struct inode *inode, struct dentry **dentry, struct vfsmount **mnt)
{
        struct task_struct *task = get_proc_task(inode);
        struct fs_struct *fs = NULL;
        int result = -ENOENT;

        if (task) {
                fs = get_fs_struct(task);
                put_task_struct(task);
        }
        if (fs) {
                read_lock(&fs->lock);
                *mnt = mntget(fs->rootmnt);
                *dentry = dget(fs->root);
                read_unlock(&fs->lock);
                result = 0;
                put_fs_struct(fs);
        }
        return result;
}

#define MAY_PTRACE(task) \
        (task == current || \
        (task->parent == current && \
        (task->ptrace & PT_PTRACED) && \
         (task->state == TASK_STOPPED || task->state == TASK_TRACED) && \
         security_ptrace(current,task) == 0))

static int proc_pid_cmdline(struct task_struct *task, char * buffer)
{
        int res = 0;
        unsigned int len;
        struct mm_struct *mm = get_task_mm(task);
        if (!mm)
                goto out;
        if (!mm->arg_end)
                goto out_mm;    /* Shh! No looking before we're done */

        len = mm->arg_end - mm->arg_start;
 
        if (len > PAGE_SIZE)
                len = PAGE_SIZE;
 
        res = access_process_vm(task, mm->arg_start, buffer, len, 0);

        // If the nul at the end of args has been overwritten, then
        // assume application is using setproctitle(3).
        if (res > 0 && buffer[res-1] != '\0' && len < PAGE_SIZE) {
                len = strnlen(buffer, res);
                if (len < res) {
                    res = len;
                } else {
                        len = mm->env_end - mm->env_start;
                        if (len > PAGE_SIZE - res)
                                len = PAGE_SIZE - res;
                        res += access_process_vm(task, mm->env_start, buffer+res, len, 0);
                        res = strnlen(buffer, res);
                }
        }
out_mm:
        mmput(mm);
out:
        return res;
}

static int proc_pid_auxv(struct task_struct *task, char *buffer)
{
        int res = 0;
        struct mm_struct *mm = get_task_mm(task);
        if (mm) {
                unsigned int nwords = 0;
                do
                        nwords += 2;
                while (mm->saved_auxv[nwords - 2] != 0); /* AT_NULL */
                res = nwords * sizeof(mm->saved_auxv[0]);
                if (res > PAGE_SIZE)
                        res = PAGE_SIZE;
                memcpy(buffer, mm->saved_auxv, res);
                mmput(mm);
        }
        return res;
}


#ifdef CONFIG_KALLSYMS
/*
 * Provides a wchan file via kallsyms in a proper one-value-per-file format.
 * Returns the resolved symbol.  If that fails, simply return the address.
 */
static int proc_pid_wchan(struct task_struct *task, char *buffer)
{
        unsigned long wchan;
        char symname[KSYM_NAME_LEN];

        wchan = get_wchan(task);

        if (lookup_symbol_name(wchan, symname) < 0)
                return sprintf(buffer, "%lu", wchan);
        else
                return sprintf(buffer, "%s", symname);
}
#endif /* CONFIG_KALLSYMS */

#ifdef CONFIG_SCHEDSTATS
/*
 * Provides /proc/PID/schedstat
 */
static int proc_pid_schedstat(struct task_struct *task, char *buffer)
{
        return sprintf(buffer, "%llu %llu %lu\n",
                        task->sched_info.cpu_time,
                        task->sched_info.run_delay,
                        task->sched_info.pcount);
}
#endif

/* The badness from the OOM killer */
unsigned long badness(struct task_struct *p, unsigned long uptime);
static int proc_oom_score(struct task_struct *task, char *buffer)
{
        unsigned long points;
        struct timespec uptime;

        do_posix_clock_monotonic_gettime(&uptime);
        read_lock(&tasklist_lock);
        points = badness(task, uptime.tv_sec);
        read_unlock(&tasklist_lock);
        return sprintf(buffer, "%lu\n", points);
}

/************************************************************************/
/*                       Here the fs part begins                        */
/************************************************************************/

/* permission checks */
static int proc_fd_access_allowed(struct inode *inode)
{
        struct task_struct *task;
        int allowed = 0;
        /* Allow access to a task's file descriptors if it is us or we
         * may use ptrace attach to the process and find out that
         * information.
         */
        task = get_proc_task(inode);
        if (task) {
                allowed = ptrace_may_attach(task);
                put_task_struct(task);
        }
        return allowed;
}

static int proc_setattr(struct dentry *dentry, struct iattr *attr)
{
        int error;
        struct inode *inode = dentry->d_inode;

        if (attr->ia_valid & ATTR_MODE)
                return -EPERM;

        error = inode_change_ok(inode, attr);
        if (!error)
                error = inode_setattr(inode, attr);
        return error;
}

static const struct inode_operations proc_def_inode_operations = {
        .setattr        = proc_setattr,
};

extern struct seq_operations mounts_op;
struct proc_mounts {
        struct seq_file m;
        int event;
};

static int mounts_open(struct inode *inode, struct file *file)
{
        struct task_struct *task = get_proc_task(inode);
        struct mnt_namespace *ns = NULL;
        struct proc_mounts *p;
        int ret = -EINVAL;

        if (task) {
                task_lock(task);
                if (task->nsproxy) {
                        ns = task->nsproxy->mnt_ns;
                        if (ns)
                                get_mnt_ns(ns);
                }
                task_unlock(task);
                put_task_struct(task);
        }

        if (ns) {
                ret = -ENOMEM;
                p = kmalloc(sizeof(struct proc_mounts), GFP_KERNEL);
                if (p) {
                        file->private_data = &p->m;
                        ret = seq_open(file, &mounts_op);
                        if (!ret) {
                                p->m.private = ns;
                                p->event = ns->event;
                                return 0;
                        }
                        kfree(p);
                }
                put_mnt_ns(ns);
        }
        return ret;
}

static int mounts_release(struct inode *inode, struct file *file)
{
        struct seq_file *m = file->private_data;
        struct mnt_namespace *ns = m->private;
        put_mnt_ns(ns);
        return seq_release(inode, file);
}

static unsigned mounts_poll(struct file *file, poll_table *wait)
{
        struct proc_mounts *p = file->private_data;
        struct mnt_namespace *ns = p->m.private;
        unsigned res = 0;

        poll_wait(file, &ns->poll, wait);

        spin_lock(&vfsmount_lock);
        if (p->event != ns->event) {
                p->event = ns->event;
                res = POLLERR;
        }
        spin_unlock(&vfsmount_lock);

        return res;
}

static const struct file_operations proc_mounts_operations = {
        .open           = mounts_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = mounts_release,
        .poll           = mounts_poll,
};

extern struct seq_operations mountstats_op;
static int mountstats_open(struct inode *inode, struct file *file)
{
        int ret = seq_open(file, &mountstats_op);

        if (!ret) {
                struct seq_file *m = file->private_data;
                struct mnt_namespace *mnt_ns = NULL;
                struct task_struct *task = get_proc_task(inode);

                if (task) {
                        task_lock(task);
                        if (task->nsproxy)
                                mnt_ns = task->nsproxy->mnt_ns;
                        if (mnt_ns)
                                get_mnt_ns(mnt_ns);
                        task_unlock(task);
                        put_task_struct(task);
                }

                if (mnt_ns)
                        m->private = mnt_ns;
                else {
                        seq_release(inode, file);
                        ret = -EINVAL;
                }
        }
        return ret;
}

static const struct file_operations proc_mountstats_operations = {
        .open           = mountstats_open,
        .read           = seq_read,
        .llseek         = seq_lseek,
        .release        = mounts_release,
};

#define PROC_BLOCK_SIZE (3*1024)                /* 4K page size but our output routines use some slack for overruns */

static ssize_t proc_info_read(struct file * file, char __user * buf,
                          size_t count, loff_t *ppos)
{
        struct inode * inode = file->f_path.dentry->d_inode;
        unsigned long page;
        ssize_t length;
        struct task_struct *task = get_proc_task(inode);

        length = -ESRCH;
        if (!task)
                goto out_no_task;

        if (count > PROC_BLOCK_SIZE)
                count = PROC_BLOCK_SIZE;

        length = -ENOMEM;
        if (!(page = __get_free_page(GFP_TEMPORARY)))
                goto out;

        length = PROC_I(inode)->op.proc_read(task, (char*)page);

        if (length >= 0)
                length = simple_read_from_buffer(buf, count, ppos, (char *)page, length);
        free_page(page);
out:
        put_task_struct(task);
out_no_task:
        return length;
}

static const struct file_operations proc_info_file_operations = {
        .read           = proc_info_read,
};

static int mem_open(struct inode* inode, struct file* file)
{
        file->private_data = (void*)((long)current->self_exec_id);
        return 0;
}

static ssize_t mem_read(struct file * file, char __user * buf,
                        size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
        char *page;
        unsigned long src = *ppos;
        int ret = -ESRCH;
        struct mm_struct *mm;

        if (!task)
                goto out_no_task;

        if (!MAY_PTRACE(task) || !ptrace_may_attach(task))
                goto out;

        ret = -ENOMEM;
        page = (char *)__get_free_page(GFP_TEMPORARY);
        if (!page)
                goto out;

        ret = 0;
 
        mm = get_task_mm(task);
        if (!mm)
                goto out_free;

        ret = -EIO;
 
        if (file->private_data != (void*)((long)current->self_exec_id))
                goto out_put;

        ret = 0;
 
        while (count > 0) {
                int this_len, retval;

                this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
                retval = access_process_vm(task, src, page, this_len, 0);
                if (!retval || !MAY_PTRACE(task) || !ptrace_may_attach(task)) {
                        if (!ret)
                                ret = -EIO;
                        break;
                }

                if (copy_to_user(buf, page, retval)) {
                        ret = -EFAULT;
                        break;
                }
 
                ret += retval;
                src += retval;
                buf += retval;
                count -= retval;
        }
        *ppos = src;

out_put:
        mmput(mm);
out_free:
        free_page((unsigned long) page);
out:
        put_task_struct(task);
out_no_task:
        return ret;
}

#define mem_write NULL

#ifndef mem_write
/* This is a security hazard */
static ssize_t mem_write(struct file * file, const char __user *buf,
                         size_t count, loff_t *ppos)
{
        int copied;
        char *page;
        struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
        unsigned long dst = *ppos;

        copied = -ESRCH;
        if (!task)
                goto out_no_task;

        if (!MAY_PTRACE(task) || !ptrace_may_attach(task))
                goto out;

        copied = -ENOMEM;
        page = (char *)__get_free_page(GFP_TEMPORARY);
        if (!page)
                goto out;

        copied = 0;
        while (count > 0) {
                int this_len, retval;

                this_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
                if (copy_from_user(page, buf, this_len)) {
                        copied = -EFAULT;
                        break;
                }
                retval = access_process_vm(task, dst, page, this_len, 1);
                if (!retval) {
                        if (!copied)
                                copied = -EIO;
                        break;
                }
                copied += retval;
                buf += retval;
                dst += retval;
                count -= retval;                        
        }
        *ppos = dst;
        free_page((unsigned long) page);
out:
        put_task_struct(task);
out_no_task:
        return copied;
}
#endif

static loff_t mem_lseek(struct file * file, loff_t offset, int orig)
{
        switch (orig) {
        case 0:
                file->f_pos = offset;
                break;
        case 1:
                file->f_pos += offset;
                break;
        default:
                return -EINVAL;
        }
        force_successful_syscall_return();
        return file->f_pos;
}

static const struct file_operations proc_mem_operations = {
        .llseek         = mem_lseek,
        .read           = mem_read,
        .write          = mem_write,
        .open           = mem_open,
};

static ssize_t environ_read(struct file *file, char __user *buf,
                        size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_dentry->d_inode);
        char *page;
        unsigned long src = *ppos;
        int ret = -ESRCH;
        struct mm_struct *mm;

        if (!task)
                goto out_no_task;

        if (!ptrace_may_attach(task))
                goto out;

        ret = -ENOMEM;
        page = (char *)__get_free_page(GFP_TEMPORARY);
        if (!page)
                goto out;

        ret = 0;

        mm = get_task_mm(task);
        if (!mm)
                goto out_free;

        while (count > 0) {
                int this_len, retval, max_len;

                this_len = mm->env_end - (mm->env_start + src);

                if (this_len <= 0)
                        break;

                max_len = (count > PAGE_SIZE) ? PAGE_SIZE : count;
                this_len = (this_len > max_len) ? max_len : this_len;

                retval = access_process_vm(task, (mm->env_start + src),
                        page, this_len, 0);

                if (retval <= 0) {
                        ret = retval;
                        break;
                }

                if (copy_to_user(buf, page, retval)) {
                        ret = -EFAULT;
                        break;
                }

                ret += retval;
                src += retval;
                buf += retval;
                count -= retval;
        }
        *ppos = src;

        mmput(mm);
out_free:
        free_page((unsigned long) page);
out:
        put_task_struct(task);
out_no_task:
        return ret;
}

static const struct file_operations proc_environ_operations = {
        .read           = environ_read,
};

static ssize_t oom_adjust_read(struct file *file, char __user *buf,
                                size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_path.dentry->d_inode);
        char buffer[PROC_NUMBUF];
        size_t len;
        int oom_adjust;

        if (!task)
                return -ESRCH;
        oom_adjust = task->oomkilladj;
        put_task_struct(task);

        len = snprintf(buffer, sizeof(buffer), "%i\n", oom_adjust);

        return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

static ssize_t oom_adjust_write(struct file *file, const char __user *buf,
                                size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char buffer[PROC_NUMBUF], *end;
        int oom_adjust;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;
        oom_adjust = simple_strtol(buffer, &end, 0);
        if ((oom_adjust < OOM_ADJUST_MIN || oom_adjust > OOM_ADJUST_MAX) &&
             oom_adjust != OOM_DISABLE)
                return -EINVAL;
        if (*end == '\n')
                end++;
        task = get_proc_task(file->f_path.dentry->d_inode);
        if (!task)
                return -ESRCH;
        if (oom_adjust < task->oomkilladj && !capable(CAP_SYS_RESOURCE)) {
                put_task_struct(task);
                return -EACCES;
        }
        task->oomkilladj = oom_adjust;
        put_task_struct(task);
        if (end - buffer == 0)
                return -EIO;
        return end - buffer;
}

static const struct file_operations proc_oom_adjust_operations = {
        .read           = oom_adjust_read,
        .write          = oom_adjust_write,
};

#ifdef CONFIG_MMU
static ssize_t clear_refs_write(struct file *file, const char __user *buf,
                                size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char buffer[PROC_NUMBUF], *end;
        struct mm_struct *mm;

        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;
        if (!simple_strtol(buffer, &end, 0))
                return -EINVAL;
        if (*end == '\n')
                end++;
        task = get_proc_task(file->f_path.dentry->d_inode);
        if (!task)
                return -ESRCH;
        mm = get_task_mm(task);
        if (mm) {
                clear_refs_smap(mm);
                mmput(mm);
        }
        put_task_struct(task);
        if (end - buffer == 0)
                return -EIO;
        return end - buffer;
}

static struct file_operations proc_clear_refs_operations = {
        .write          = clear_refs_write,
};
#endif

#ifdef CONFIG_AUDITSYSCALL
#define TMPBUFLEN 21
static ssize_t proc_loginuid_read(struct file * file, char __user * buf,
                                  size_t count, loff_t *ppos)
{
        struct inode * inode = file->f_path.dentry->d_inode;
        struct task_struct *task = get_proc_task(inode);
        ssize_t length;
        char tmpbuf[TMPBUFLEN];

        if (!task)
                return -ESRCH;
        length = scnprintf(tmpbuf, TMPBUFLEN, "%u",
                                audit_get_loginuid(task->audit_context));
        put_task_struct(task);
        return simple_read_from_buffer(buf, count, ppos, tmpbuf, length);
}

static ssize_t proc_loginuid_write(struct file * file, const char __user * buf,
                                   size_t count, loff_t *ppos)
{
        struct inode * inode = file->f_path.dentry->d_inode;
        char *page, *tmp;
        ssize_t length;
        uid_t loginuid;

        if (!capable(CAP_AUDIT_CONTROL))
                return -EPERM;

        if (current != pid_task(proc_pid(inode), PIDTYPE_PID))
                return -EPERM;

        if (count >= PAGE_SIZE)
                count = PAGE_SIZE - 1;

        if (*ppos != 0) {
                /* No partial writes. */
                return -EINVAL;
        }
        page = (char*)__get_free_page(GFP_TEMPORARY);
        if (!page)
                return -ENOMEM;
        length = -EFAULT;
        if (copy_from_user(page, buf, count))
                goto out_free_page;

        page[count] = '\0';
        loginuid = simple_strtoul(page, &tmp, 10);
        if (tmp == page) {
                length = -EINVAL;
                goto out_free_page;

        }
        length = audit_set_loginuid(current, loginuid);
        if (likely(length == 0))
                length = count;

out_free_page:
        free_page((unsigned long) page);
        return length;
}

static const struct file_operations proc_loginuid_operations = {
        .read           = proc_loginuid_read,
        .write          = proc_loginuid_write,
};
#endif

#ifdef CONFIG_FAULT_INJECTION
static ssize_t proc_fault_inject_read(struct file * file, char __user * buf,
                                      size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_dentry->d_inode);
        char buffer[PROC_NUMBUF];
        size_t len;
        int make_it_fail;

        if (!task)
                return -ESRCH;
        make_it_fail = task->make_it_fail;
        put_task_struct(task);

        len = snprintf(buffer, sizeof(buffer), "%i\n", make_it_fail);

        return simple_read_from_buffer(buf, count, ppos, buffer, len);
}

static ssize_t proc_fault_inject_write(struct file * file,
                        const char __user * buf, size_t count, loff_t *ppos)
{
        struct task_struct *task;
        char buffer[PROC_NUMBUF], *end;
        int make_it_fail;

        if (!capable(CAP_SYS_RESOURCE))
                return -EPERM;
        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                return -EFAULT;
        make_it_fail = simple_strtol(buffer, &end, 0);
        if (*end == '\n')
                end++;
        task = get_proc_task(file->f_dentry->d_inode);
        if (!task)
                return -ESRCH;
        task->make_it_fail = make_it_fail;
        put_task_struct(task);
        if (end - buffer == 0)
                return -EIO;
        return end - buffer;
}

static const struct file_operations proc_fault_inject_operations = {
        .read           = proc_fault_inject_read,
        .write          = proc_fault_inject_write,
};
#endif

#ifdef CONFIG_SCHED_DEBUG
/*
 * Print out various scheduling related per-task fields:
 */
static int sched_show(struct seq_file *m, void *v)
{
        struct inode *inode = m->private;
        struct task_struct *p;

        WARN_ON(!inode);

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;
        proc_sched_show_task(p, m);

        put_task_struct(p);

        return 0;
}

static ssize_t
sched_write(struct file *file, const char __user *buf,
            size_t count, loff_t *offset)
{
        struct inode *inode = file->f_path.dentry->d_inode;
        struct task_struct *p;

        WARN_ON(!inode);

        p = get_proc_task(inode);
        if (!p)
                return -ESRCH;
        proc_sched_set_task(p);

        put_task_struct(p);

        return count;
}

static int sched_open(struct inode *inode, struct file *filp)
{
        int ret;

        ret = single_open(filp, sched_show, NULL);
        if (!ret) {
                struct seq_file *m = filp->private_data;

                m->private = inode;
        }
        return ret;
}

static const struct file_operations proc_pid_sched_operations = {
        .open           = sched_open,
        .read           = seq_read,
        .write          = sched_write,
        .llseek         = seq_lseek,
        .release        = single_release,
};

#endif

static void *proc_pid_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        struct inode *inode = dentry->d_inode;
        int error = -EACCES;

        /* We don't need a base pointer in the /proc filesystem */
        path_release(nd);

        /* Are we allowed to snoop on the tasks file descriptors? */
        if (!proc_fd_access_allowed(inode))
                goto out;

        error = PROC_I(inode)->op.proc_get_link(inode, &nd->dentry, &nd->mnt);
        nd->last_type = LAST_BIND;
out:
        return ERR_PTR(error);
}

static int do_proc_readlink(struct dentry *dentry, struct vfsmount *mnt,
                            char __user *buffer, int buflen)
{
        struct inode * inode;
        char *tmp = (char*)__get_free_page(GFP_TEMPORARY);
        char *path;
        int len;

        if (!tmp)
                return -ENOMEM;

        inode = dentry->d_inode;
        path = d_path(dentry, mnt, tmp, PAGE_SIZE);
        len = PTR_ERR(path);
        if (IS_ERR(path))
                goto out;
        len = tmp + PAGE_SIZE - 1 - path;

        if (len > buflen)
                len = buflen;
        if (copy_to_user(buffer, path, len))
                len = -EFAULT;
 out:
        free_page((unsigned long)tmp);
        return len;
}

static int proc_pid_readlink(struct dentry * dentry, char __user * buffer, int buflen)
{
        int error = -EACCES;
        struct inode *inode = dentry->d_inode;
        struct dentry *de;
        struct vfsmount *mnt = NULL;

        /* Are we allowed to snoop on the tasks file descriptors? */
        if (!proc_fd_access_allowed(inode))
                goto out;

        error = PROC_I(inode)->op.proc_get_link(inode, &de, &mnt);
        if (error)
                goto out;

        error = do_proc_readlink(de, mnt, buffer, buflen);
        dput(de);
        mntput(mnt);
out:
        return error;
}

static const struct inode_operations proc_pid_link_inode_operations = {
        .readlink       = proc_pid_readlink,
        .follow_link    = proc_pid_follow_link,
        .setattr        = proc_setattr,
};


/* building an inode */

static int task_dumpable(struct task_struct *task)
{
        int dumpable = 0;
        struct mm_struct *mm;

        task_lock(task);
        mm = task->mm;
        if (mm)
                dumpable = get_dumpable(mm);
        task_unlock(task);
        if(dumpable == 1)
                return 1;
        return 0;
}


static struct inode *proc_pid_make_inode(struct super_block * sb, struct task_struct *task)
{
        struct inode * inode;
        struct proc_inode *ei;

        /* We need a new inode */

        inode = new_inode(sb);
        if (!inode)
                goto out;

        /* Common stuff */
        ei = PROC_I(inode);
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
        inode->i_op = &proc_def_inode_operations;

        /*
         * grab the reference to task.
         */
        ei->pid = get_task_pid(task, PIDTYPE_PID);
        if (!ei->pid)
                goto out_unlock;

        inode->i_uid = 0;
        inode->i_gid = 0;
        if (task_dumpable(task)) {
                inode->i_uid = task->euid;
                inode->i_gid = task->egid;
        }
        security_task_to_inode(task, inode);

out:
        return inode;

out_unlock:
        iput(inode);
        return NULL;
}

static int pid_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
        struct task_struct *task;
        generic_fillattr(inode, stat);

        rcu_read_lock();
        stat->uid = 0;
        stat->gid = 0;
        task = pid_task(proc_pid(inode), PIDTYPE_PID);
        if (task) {
                if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
                    task_dumpable(task)) {
                        stat->uid = task->euid;
                        stat->gid = task->egid;
                }
        }
        rcu_read_unlock();
        return 0;
}

/* dentry stuff */

/*
 *      Exceptional case: normally we are not allowed to unhash a busy
 * directory. In this case, however, we can do it - no aliasing problems
 * due to the way we treat inodes.
 *
 * Rewrite the inode's ownerships here because the owning task may have
 * performed a setuid(), etc.
 *
 * Before the /proc/pid/status file was created the only way to read
 * the effective uid of a /process was to stat /proc/pid.  Reading
 * /proc/pid/status is slow enough that procps and other packages
 * kept stating /proc/pid.  To keep the rules in /proc simple I have
 * made this apply to all per process world readable and executable
 * directories.
 */
static int pid_revalidate(struct dentry *dentry, struct nameidata *nd)
{
        struct inode *inode = dentry->d_inode;
        struct task_struct *task = get_proc_task(inode);
        if (task) {
                if ((inode->i_mode == (S_IFDIR|S_IRUGO|S_IXUGO)) ||
                    task_dumpable(task)) {
                        inode->i_uid = task->euid;
                        inode->i_gid = task->egid;
                } else {
                        inode->i_uid = 0;
                        inode->i_gid = 0;
                }
                inode->i_mode &= ~(S_ISUID | S_ISGID);
                security_task_to_inode(task, inode);
                put_task_struct(task);
                return 1;
        }
        d_drop(dentry);
        return 0;
}

static int pid_delete_dentry(struct dentry * dentry)
{
        /* Is the task we represent dead?
         * If so, then don't put the dentry on the lru list,
         * kill it immediately.
         */
        return !proc_pid(dentry->d_inode)->tasks[PIDTYPE_PID].first;
}

static struct dentry_operations pid_dentry_operations =
{
        .d_revalidate   = pid_revalidate,
        .d_delete       = pid_delete_dentry,
};

/* Lookups */

typedef struct dentry *instantiate_t(struct inode *, struct dentry *,
                                struct task_struct *, const void *);

/*
 * Fill a directory entry.
 *
 * If possible create the dcache entry and derive our inode number and
 * file type from dcache entry.
 *
 * Since all of the proc inode numbers are dynamically generated, the inode
 * numbers do not exist until the inode is cache.  This means creating the
 * the dcache entry in readdir is necessary to keep the inode numbers
 * reported by readdir in sync with the inode numbers reported
 * by stat.
 */
static int proc_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
        char *name, int len,
        instantiate_t instantiate, struct task_struct *task, const void *ptr)
{
        struct dentry *child, *dir = filp->f_path.dentry;
        struct inode *inode;
        struct qstr qname;
        ino_t ino = 0;
        unsigned type = DT_UNKNOWN;

        qname.name = name;
        qname.len  = len;
        qname.hash = full_name_hash(name, len);

        child = d_lookup(dir, &qname);
        if (!child) {
                struct dentry *new;
                new = d_alloc(dir, &qname);
                if (new) {
                        child = instantiate(dir->d_inode, new, task, ptr);
                        if (child)
                                dput(new);
                        else
                                child = new;
                }
        }
        if (!child || IS_ERR(child) || !child->d_inode)
                goto end_instantiate;
        inode = child->d_inode;
        if (inode) {
                ino = inode->i_ino;
                type = inode->i_mode >> 12;
        }
        dput(child);
end_instantiate:
        if (!ino)
                ino = find_inode_number(dir, &qname);
        if (!ino)
                ino = 1;
        return filldir(dirent, name, len, filp->f_pos, ino, type);
}

static unsigned name_to_int(struct dentry *dentry)
{
        const char *name = dentry->d_name.name;
        int len = dentry->d_name.len;
        unsigned n = 0;

        if (len > 1 && *name == '0')
                goto out;
        while (len-- > 0) {
                unsigned c = *name++ - '0';
                if (c > 9)
                        goto out;
                if (n >= (~0U-9)/10)
                        goto out;
                n *= 10;
                n += c;
        }
        return n;
out:
        return ~0U;
}

#define PROC_FDINFO_MAX 64

static int proc_fd_info(struct inode *inode, struct dentry **dentry,
                        struct vfsmount **mnt, char *info)
{
        struct task_struct *task = get_proc_task(inode);
        struct files_struct *files = NULL;
        struct file *file;
        int fd = proc_fd(inode);

        if (task) {
                files = get_files_struct(task);
                put_task_struct(task);
        }
        if (files) {
                /*
                 * We are not taking a ref to the file structure, so we must
                 * hold ->file_lock.
                 */
                spin_lock(&files->file_lock);
                file = fcheck_files(files, fd);
                if (file) {
                        if (mnt)
                                *mnt = mntget(file->f_path.mnt);
                        if (dentry)
                                *dentry = dget(file->f_path.dentry);
                        if (info)
                                snprintf(info, PROC_FDINFO_MAX,
                                         "pos:\t%lli\n"
                                         "flags:\t0%o\n",
                                         (long long) file->f_pos,
                                         file->f_flags);
                        spin_unlock(&files->file_lock);
                        put_files_struct(files);
                        return 0;
                }
                spin_unlock(&files->file_lock);
                put_files_struct(files);
        }
        return -ENOENT;
}

static int proc_fd_link(struct inode *inode, struct dentry **dentry,
                        struct vfsmount **mnt)
{
        return proc_fd_info(inode, dentry, mnt, NULL);
}

static int tid_fd_revalidate(struct dentry *dentry, struct nameidata *nd)
{
        struct inode *inode = dentry->d_inode;
        struct task_struct *task = get_proc_task(inode);
        int fd = proc_fd(inode);
        struct files_struct *files;

        if (task) {
                files = get_files_struct(task);
                if (files) {
                        rcu_read_lock();
                        if (fcheck_files(files, fd)) {
                                rcu_read_unlock();
                                put_files_struct(files);
                                if (task_dumpable(task)) {
                                        inode->i_uid = task->euid;
                                        inode->i_gid = task->egid;
                                } else {
                                        inode->i_uid = 0;
                                        inode->i_gid = 0;
                                }
                                inode->i_mode &= ~(S_ISUID | S_ISGID);
                                security_task_to_inode(task, inode);
                                put_task_struct(task);
                                return 1;
                        }
                        rcu_read_unlock();
                        put_files_struct(files);
                }
                put_task_struct(task);
        }
        d_drop(dentry);
        return 0;
}

static struct dentry_operations tid_fd_dentry_operations =
{
        .d_revalidate   = tid_fd_revalidate,
        .d_delete       = pid_delete_dentry,
};

static struct dentry *proc_fd_instantiate(struct inode *dir,
        struct dentry *dentry, struct task_struct *task, const void *ptr)
{
        unsigned fd = *(const unsigned *)ptr;
        struct file *file;
        struct files_struct *files;
        struct inode *inode;
        struct proc_inode *ei;
        struct dentry *error = ERR_PTR(-ENOENT);

        inode = proc_pid_make_inode(dir->i_sb, task);
        if (!inode)
                goto out;
        ei = PROC_I(inode);
        ei->fd = fd;
        files = get_files_struct(task);
        if (!files)
                goto out_iput;
        inode->i_mode = S_IFLNK;

        /*
         * We are not taking a ref to the file structure, so we must
         * hold ->file_lock.
         */
        spin_lock(&files->file_lock);
        file = fcheck_files(files, fd);
        if (!file)
                goto out_unlock;
        if (file->f_mode & 1)
                inode->i_mode |= S_IRUSR | S_IXUSR;
        if (file->f_mode & 2)
                inode->i_mode |= S_IWUSR | S_IXUSR;
        spin_unlock(&files->file_lock);
        put_files_struct(files);

        inode->i_op = &proc_pid_link_inode_operations;
        inode->i_size = 64;
        ei->op.proc_get_link = proc_fd_link;
        dentry->d_op = &tid_fd_dentry_operations;
        d_add(dentry, inode);
        /* Close the race of the process dying before we return the dentry */
        if (tid_fd_revalidate(dentry, NULL))
                error = NULL;

 out:
        return error;
out_unlock:
        spin_unlock(&files->file_lock);
        put_files_struct(files);
out_iput:
        iput(inode);
        goto out;
}

static struct dentry *proc_lookupfd_common(struct inode *dir,
                                           struct dentry *dentry,
                                           instantiate_t instantiate)
{
        struct task_struct *task = get_proc_task(dir);
        unsigned fd = name_to_int(dentry);
        struct dentry *result = ERR_PTR(-ENOENT);

        if (!task)
                goto out_no_task;
        if (fd == ~0U)
                goto out;

        result = instantiate(dir, dentry, task, &fd);
out:
        put_task_struct(task);
out_no_task:
        return result;
}

static int proc_readfd_common(struct file * filp, void * dirent,
                              filldir_t filldir, instantiate_t instantiate)
{
        struct dentry *dentry = filp->f_path.dentry;
        struct inode *inode = dentry->d_inode;
        struct task_struct *p = get_proc_task(inode);
        unsigned int fd, tid, ino;
        int retval;
        struct files_struct * files;
        struct fdtable *fdt;

        retval = -ENOENT;
        if (!p)
                goto out_no_task;
        retval = 0;
        tid = p->pid;

        fd = filp->f_pos;
        switch (fd) {
                case 0:
                        if (filldir(dirent, ".", 1, 0, inode->i_ino, DT_DIR) < 0)
                                goto out;
                        filp->f_pos++;
                case 1:
                        ino = parent_ino(dentry);
                        if (filldir(dirent, "..", 2, 1, ino, DT_DIR) < 0)
                                goto out;
                        filp->f_pos++;
                default:
                        files = get_files_struct(p);
                        if (!files)
                                goto out;
                        rcu_read_lock();
                        fdt = files_fdtable(files);
                        for (fd = filp->f_pos-2;
                             fd < fdt->max_fds;
                             fd++, filp->f_pos++) {
                                char name[PROC_NUMBUF];
                                int len;

                                if (!fcheck_files(files, fd))
                                        continue;
                                rcu_read_unlock();

                                len = snprintf(name, sizeof(name), "%d", fd);
                                if (proc_fill_cache(filp, dirent, filldir,
                                                    name, len, instantiate,
                                                    p, &fd) < 0) {
                                        rcu_read_lock();
                                        break;
                                }
                                rcu_read_lock();
                        }
                        rcu_read_unlock();
                        put_files_struct(files);
        }
out:
        put_task_struct(p);
out_no_task:
        return retval;
}

static struct dentry *proc_lookupfd(struct inode *dir, struct dentry *dentry,
                                    struct nameidata *nd)
{
        return proc_lookupfd_common(dir, dentry, proc_fd_instantiate);
}

static int proc_readfd(struct file *filp, void *dirent, filldir_t filldir)
{
        return proc_readfd_common(filp, dirent, filldir, proc_fd_instantiate);
}

static ssize_t proc_fdinfo_read(struct file *file, char __user *buf,
                                      size_t len, loff_t *ppos)
{
        char tmp[PROC_FDINFO_MAX];
        int err = proc_fd_info(file->f_path.dentry->d_inode, NULL, NULL, tmp);
        if (!err)
                err = simple_read_from_buffer(buf, len, ppos, tmp, strlen(tmp));
        return err;
}

static const struct file_operations proc_fdinfo_file_operations = {
        .open           = nonseekable_open,
        .read           = proc_fdinfo_read,
};

static const struct file_operations proc_fd_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_readfd,
};

/*
 * /proc/pid/fd needs a special permission handler so that a process can still
 * access /proc/self/fd after it has executed a setuid().
 */
static int proc_fd_permission(struct inode *inode, int mask,
                                struct nameidata *nd)
{
        int rv;

        rv = generic_permission(inode, mask, NULL);
        if (rv == 0)
                return 0;
        if (task_pid(current) == proc_pid(inode))
                rv = 0;
        return rv;
}

/*
 * proc directories can do almost nothing..
 */
static const struct inode_operations proc_fd_inode_operations = {
        .lookup         = proc_lookupfd,
        .permission     = proc_fd_permission,
        .setattr        = proc_setattr,
};

static struct dentry *proc_fdinfo_instantiate(struct inode *dir,
        struct dentry *dentry, struct task_struct *task, const void *ptr)
{
        unsigned fd = *(unsigned *)ptr;
        struct inode *inode;
        struct proc_inode *ei;
        struct dentry *error = ERR_PTR(-ENOENT);

        inode = proc_pid_make_inode(dir->i_sb, task);
        if (!inode)
                goto out;
        ei = PROC_I(inode);
        ei->fd = fd;
        inode->i_mode = S_IFREG | S_IRUSR;
        inode->i_fop = &proc_fdinfo_file_operations;
        dentry->d_op = &tid_fd_dentry_operations;
        d_add(dentry, inode);
        /* Close the race of the process dying before we return the dentry */
        if (tid_fd_revalidate(dentry, NULL))
                error = NULL;

 out:
        return error;
}

static struct dentry *proc_lookupfdinfo(struct inode *dir,
                                        struct dentry *dentry,
                                        struct nameidata *nd)
{
        return proc_lookupfd_common(dir, dentry, proc_fdinfo_instantiate);
}

static int proc_readfdinfo(struct file *filp, void *dirent, filldir_t filldir)
{
        return proc_readfd_common(filp, dirent, filldir,
                                  proc_fdinfo_instantiate);
}

static const struct file_operations proc_fdinfo_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_readfdinfo,
};

/*
 * proc directories can do almost nothing..
 */
static const struct inode_operations proc_fdinfo_inode_operations = {
        .lookup         = proc_lookupfdinfo,
        .setattr        = proc_setattr,
};


static struct dentry *proc_pident_instantiate(struct inode *dir,
        struct dentry *dentry, struct task_struct *task, const void *ptr)
{
        const struct pid_entry *p = ptr;
        struct inode *inode;
        struct proc_inode *ei;
        struct dentry *error = ERR_PTR(-EINVAL);

        inode = proc_pid_make_inode(dir->i_sb, task);
        if (!inode)
                goto out;

        ei = PROC_I(inode);
        inode->i_mode = p->mode;
        if (S_ISDIR(inode->i_mode))
                inode->i_nlink = 2;     /* Use getattr to fix if necessary */
        if (p->iop)
                inode->i_op = p->iop;
        if (p->fop)
                inode->i_fop = p->fop;
        ei->op = p->op;
        dentry->d_op = &pid_dentry_operations;
        d_add(dentry, inode);
        /* Close the race of the process dying before we return the dentry */
        if (pid_revalidate(dentry, NULL))
                error = NULL;
out:
        return error;
}

static struct dentry *proc_pident_lookup(struct inode *dir, 
                                         struct dentry *dentry,
                                         const struct pid_entry *ents,
                                         unsigned int nents)
{
        struct inode *inode;
        struct dentry *error;
        struct task_struct *task = get_proc_task(dir);
        const struct pid_entry *p, *last;

        error = ERR_PTR(-ENOENT);
        inode = NULL;

        if (!task)
                goto out_no_task;

        /*
         * Yes, it does not scale. And it should not. Don't add
         * new entries into /proc/<tgid>/ without very good reasons.
         */
        last = &ents[nents - 1];
        for (p = ents; p <= last; p++) {
                if (p->len != dentry->d_name.len)
                        continue;
                if (!memcmp(dentry->d_name.name, p->name, p->len))
                        break;
        }
        if (p > last)
                goto out;

        error = proc_pident_instantiate(dir, dentry, task, p);
out:
        put_task_struct(task);
out_no_task:
        return error;
}

static int proc_pident_fill_cache(struct file *filp, void *dirent,
        filldir_t filldir, struct task_struct *task, const struct pid_entry *p)
{
        return proc_fill_cache(filp, dirent, filldir, p->name, p->len,
                                proc_pident_instantiate, task, p);
}

static int proc_pident_readdir(struct file *filp,
                void *dirent, filldir_t filldir,
                const struct pid_entry *ents, unsigned int nents)
{
        int i;
        int pid;
        struct dentry *dentry = filp->f_path.dentry;
        struct inode *inode = dentry->d_inode;
        struct task_struct *task = get_proc_task(inode);
        const struct pid_entry *p, *last;
        ino_t ino;
        int ret;

        ret = -ENOENT;
        if (!task)
                goto out_no_task;

        ret = 0;
        pid = task->pid;
        i = filp->f_pos;
        switch (i) {
        case 0:
                ino = inode->i_ino;
                if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
                        goto out;
                i++;
                filp->f_pos++;
                /* fall through */
        case 1:
                ino = parent_ino(dentry);
                if (filldir(dirent, "..", 2, i, ino, DT_DIR) < 0)
                        goto out;
                i++;
                filp->f_pos++;
                /* fall through */
        default:
                i -= 2;
                if (i >= nents) {
                        ret = 1;
                        goto out;
                }
                p = ents + i;
                last = &ents[nents - 1];
                while (p <= last) {
                        if (proc_pident_fill_cache(filp, dirent, filldir, task, p) < 0)
                                goto out;
                        filp->f_pos++;
                        p++;
                }
        }

        ret = 1;
out:
        put_task_struct(task);
out_no_task:
        return ret;
}

#ifdef CONFIG_SECURITY
static ssize_t proc_pid_attr_read(struct file * file, char __user * buf,
                                  size_t count, loff_t *ppos)
{
        struct inode * inode = file->f_path.dentry->d_inode;
        char *p = NULL;
        ssize_t length;
        struct task_struct *task = get_proc_task(inode);

        if (!task)
                return -ESRCH;

        length = security_getprocattr(task,
                                      (char*)file->f_path.dentry->d_name.name,
                                      &p);
        put_task_struct(task);
        if (length > 0)
                length = simple_read_from_buffer(buf, count, ppos, p, length);
        kfree(p);
        return length;
}

static ssize_t proc_pid_attr_write(struct file * file, const char __user * buf,
                                   size_t count, loff_t *ppos)
{
        struct inode * inode = file->f_path.dentry->d_inode;
        char *page;
        ssize_t length;
        struct task_struct *task = get_proc_task(inode);

        length = -ESRCH;
        if (!task)
                goto out_no_task;
        if (count > PAGE_SIZE)
                count = PAGE_SIZE;

        /* No partial writes. */
        length = -EINVAL;
        if (*ppos != 0)
                goto out;

        length = -ENOMEM;
        page = (char*)__get_free_page(GFP_TEMPORARY);
        if (!page)
                goto out;

        length = -EFAULT;
        if (copy_from_user(page, buf, count))
                goto out_free;

        length = security_setprocattr(task,
                                      (char*)file->f_path.dentry->d_name.name,
                                      (void*)page, count);
out_free:
        free_page((unsigned long) page);
out:
        put_task_struct(task);
out_no_task:
        return length;
}

static const struct file_operations proc_pid_attr_operations = {
        .read           = proc_pid_attr_read,
        .write          = proc_pid_attr_write,
};

static const struct pid_entry attr_dir_stuff[] = {
        REG("current",    S_IRUGO|S_IWUGO, pid_attr),
        REG("prev",       S_IRUGO,         pid_attr),
        REG("exec",       S_IRUGO|S_IWUGO, pid_attr),
        REG("fscreate",   S_IRUGO|S_IWUGO, pid_attr),
        REG("keycreate",  S_IRUGO|S_IWUGO, pid_attr),
        REG("sockcreate", S_IRUGO|S_IWUGO, pid_attr),
};

static int proc_attr_dir_readdir(struct file * filp,
                             void * dirent, filldir_t filldir)
{
        return proc_pident_readdir(filp,dirent,filldir,
                                   attr_dir_stuff,ARRAY_SIZE(attr_dir_stuff));
}

static const struct file_operations proc_attr_dir_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_attr_dir_readdir,
};

static struct dentry *proc_attr_dir_lookup(struct inode *dir,
                                struct dentry *dentry, struct nameidata *nd)
{
        return proc_pident_lookup(dir, dentry,
                                  attr_dir_stuff, ARRAY_SIZE(attr_dir_stuff));
}

static const struct inode_operations proc_attr_dir_inode_operations = {
        .lookup         = proc_attr_dir_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
};

#endif

#if defined(USE_ELF_CORE_DUMP) && defined(CONFIG_ELF_CORE)
static ssize_t proc_coredump_filter_read(struct file *file, char __user *buf,
                                         size_t count, loff_t *ppos)
{
        struct task_struct *task = get_proc_task(file->f_dentry->d_inode);
        struct mm_struct *mm;
        char buffer[PROC_NUMBUF];
        size_t len;
        int ret;

        if (!task)
                return -ESRCH;

        ret = 0;
        mm = get_task_mm(task);
        if (mm) {
                len = snprintf(buffer, sizeof(buffer), "%08lx\n",
                               ((mm->flags & MMF_DUMP_FILTER_MASK) >>
                                MMF_DUMP_FILTER_SHIFT));
                mmput(mm);
                ret = simple_read_from_buffer(buf, count, ppos, buffer, len);
        }

        put_task_struct(task);

        return ret;
}

static ssize_t proc_coredump_filter_write(struct file *file,
                                          const char __user *buf,
                                          size_t count,
                                          loff_t *ppos)
{
        struct task_struct *task;
        struct mm_struct *mm;
        char buffer[PROC_NUMBUF], *end;
        unsigned int val;
        int ret;
        int i;
        unsigned long mask;

        ret = -EFAULT;
        memset(buffer, 0, sizeof(buffer));
        if (count > sizeof(buffer) - 1)
                count = sizeof(buffer) - 1;
        if (copy_from_user(buffer, buf, count))
                goto out_no_task;

        ret = -EINVAL;
        val = (unsigned int)simple_strtoul(buffer, &end, 0);
        if (*end == '\n')
                end++;
        if (end - buffer == 0)
                goto out_no_task;

        ret = -ESRCH;
        task = get_proc_task(file->f_dentry->d_inode);
        if (!task)
                goto out_no_task;

        ret = end - buffer;
        mm = get_task_mm(task);
        if (!mm)
                goto out_no_mm;

        for (i = 0, mask = 1; i < MMF_DUMP_FILTER_BITS; i++, mask <<= 1) {
                if (val & mask)
                        set_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
                else
                        clear_bit(i + MMF_DUMP_FILTER_SHIFT, &mm->flags);
        }

        mmput(mm);
 out_no_mm:
        put_task_struct(task);
 out_no_task:
        return ret;
}

static const struct file_operations proc_coredump_filter_operations = {
        .read           = proc_coredump_filter_read,
        .write          = proc_coredump_filter_write,
};
#endif

/*
 * /proc/self:
 */
static int proc_self_readlink(struct dentry *dentry, char __user *buffer,
                              int buflen)
{
        char tmp[PROC_NUMBUF];
        sprintf(tmp, "%d", current->tgid);
        return vfs_readlink(dentry,buffer,buflen,tmp);
}

static void *proc_self_follow_link(struct dentry *dentry, struct nameidata *nd)
{
        char tmp[PROC_NUMBUF];
        sprintf(tmp, "%d", current->tgid);
        return ERR_PTR(vfs_follow_link(nd,tmp));
}

static const struct inode_operations proc_self_inode_operations = {
        .readlink       = proc_self_readlink,
        .follow_link    = proc_self_follow_link,
};

/*
 * proc base
 *
 * These are the directory entries in the root directory of /proc
 * that properly belong to the /proc filesystem, as they describe
 * describe something that is process related.
 */
static const struct pid_entry proc_base_stuff[] = {
        NOD("self", S_IFLNK|S_IRWXUGO,
                &proc_self_inode_operations, NULL, {}),
};

/*
 *      Exceptional case: normally we are not allowed to unhash a busy
 * directory. In this case, however, we can do it - no aliasing problems
 * due to the way we treat inodes.
 */
static int proc_base_revalidate(struct dentry *dentry, struct nameidata *nd)
{
        struct inode *inode = dentry->d_inode;
        struct task_struct *task = get_proc_task(inode);
        if (task) {
                put_task_struct(task);
                return 1;
        }
        d_drop(dentry);
        return 0;
}

static struct dentry_operations proc_base_dentry_operations =
{
        .d_revalidate   = proc_base_revalidate,
        .d_delete       = pid_delete_dentry,
};

static struct dentry *proc_base_instantiate(struct inode *dir,
        struct dentry *dentry, struct task_struct *task, const void *ptr)
{
        const struct pid_entry *p = ptr;
        struct inode *inode;
        struct proc_inode *ei;
        struct dentry *error = ERR_PTR(-EINVAL);

        /* Allocate the inode */
        error = ERR_PTR(-ENOMEM);
        inode = new_inode(dir->i_sb);
        if (!inode)
                goto out;

        /* Initialize the inode */
        ei = PROC_I(inode);
        inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;

        /*
         * grab the reference to the task.
         */
        ei->pid = get_task_pid(task, PIDTYPE_PID);
        if (!ei->pid)
                goto out_iput;

        inode->i_uid = 0;
        inode->i_gid = 0;
        inode->i_mode = p->mode;
        if (S_ISDIR(inode->i_mode))
                inode->i_nlink = 2;
        if (S_ISLNK(inode->i_mode))
                inode->i_size = 64;
        if (p->iop)
                inode->i_op = p->iop;
        if (p->fop)
                inode->i_fop = p->fop;
        ei->op = p->op;
        dentry->d_op = &proc_base_dentry_operations;
        d_add(dentry, inode);
        error = NULL;
out:
        return error;
out_iput:
        iput(inode);
        goto out;
}

static struct dentry *proc_base_lookup(struct inode *dir, struct dentry *dentry)
{
        struct dentry *error;
        struct task_struct *task = get_proc_task(dir);
        const struct pid_entry *p, *last;

        error = ERR_PTR(-ENOENT);

        if (!task)
                goto out_no_task;

        /* Lookup the directory entry */
        last = &proc_base_stuff[ARRAY_SIZE(proc_base_stuff) - 1];
        for (p = proc_base_stuff; p <= last; p++) {
                if (p->len != dentry->d_name.len)
                        continue;
                if (!memcmp(dentry->d_name.name, p->name, p->len))
                        break;
        }
        if (p > last)
                goto out;

        error = proc_base_instantiate(dir, dentry, task, p);

out:
        put_task_struct(task);
out_no_task:
        return error;
}

static int proc_base_fill_cache(struct file *filp, void *dirent,
        filldir_t filldir, struct task_struct *task, const struct pid_entry *p)
{
        return proc_fill_cache(filp, dirent, filldir, p->name, p->len,
                                proc_base_instantiate, task, p);
}

#ifdef CONFIG_TASK_IO_ACCOUNTING
static int proc_pid_io_accounting(struct task_struct *task, char *buffer)
{
        return sprintf(buffer,
#ifdef CONFIG_TASK_XACCT
                        "rchar: %llu\n"
                        "wchar: %llu\n"
                        "syscr: %llu\n"
                        "syscw: %llu\n"
#endif
                        "read_bytes: %llu\n"
                        "write_bytes: %llu\n"
                        "cancelled_write_bytes: %llu\n",
#ifdef CONFIG_TASK_XACCT
                        (unsigned long long)task->rchar,
                        (unsigned long long)task->wchar,
                        (unsigned long long)task->syscr,
                        (unsigned long long)task->syscw,
#endif
                        (unsigned long long)task->ioac.read_bytes,
                        (unsigned long long)task->ioac.write_bytes,
                        (unsigned long long)task->ioac.cancelled_write_bytes);
}
#endif

/*
 * Thread groups
 */
static const struct file_operations proc_task_operations;
static const struct inode_operations proc_task_inode_operations;

static const struct pid_entry tgid_base_stuff[] = {
        DIR("task",       S_IRUGO|S_IXUGO, task),
        DIR("fd",         S_IRUSR|S_IXUSR, fd),
        DIR("fdinfo",     S_IRUSR|S_IXUSR, fdinfo),
        REG("environ",    S_IRUSR, environ),
        INF("auxv",       S_IRUSR, pid_auxv),
        INF("status",     S_IRUGO, pid_status),
#ifdef CONFIG_SCHED_DEBUG
        REG("sched",      S_IRUGO|S_IWUSR, pid_sched),
#endif
        INF("cmdline",    S_IRUGO, pid_cmdline),
        INF("stat",       S_IRUGO, tgid_stat),
        INF("statm",      S_IRUGO, pid_statm),
        REG("maps",       S_IRUGO, maps),
#ifdef CONFIG_NUMA
        REG("numa_maps",  S_IRUGO, numa_maps),
#endif
        REG("mem",        S_IRUSR|S_IWUSR, mem),
        LNK("cwd",        cwd),
        LNK("root",       root),
        LNK("exe",        exe),
        REG("mounts",     S_IRUGO, mounts),
        REG("mountstats", S_IRUSR, mountstats),
#ifdef CONFIG_MMU
        REG("clear_refs", S_IWUSR, clear_refs),
        REG("smaps",      S_IRUGO, smaps),
#endif
#ifdef CONFIG_SECURITY
        DIR("attr",       S_IRUGO|S_IXUGO, attr_dir),
#endif
#ifdef CONFIG_KALLSYMS
        INF("wchan",      S_IRUGO, pid_wchan),
#endif
#ifdef CONFIG_SCHEDSTATS
        INF("schedstat",  S_IRUGO, pid_schedstat),
#endif
#ifdef CONFIG_CPUSETS
        REG("cpuset",     S_IRUGO, cpuset),
#endif
        INF("oom_score",  S_IRUGO, oom_score),
        REG("oom_adj",    S_IRUGO|S_IWUSR, oom_adjust),
#ifdef CONFIG_AUDITSYSCALL
        REG("loginuid",   S_IWUSR|S_IRUGO, loginuid),
#endif
#ifdef CONFIG_FAULT_INJECTION
        REG("make-it-fail", S_IRUGO|S_IWUSR, fault_inject),
#endif
#if defined(USE_ELF_CORE_DUMP) && defined(CONFIG_ELF_CORE)
        REG("coredump_filter", S_IRUGO|S_IWUSR, coredump_filter),
#endif
#ifdef CONFIG_TASK_IO_ACCOUNTING
        INF("io",       S_IRUGO, pid_io_accounting),
#endif
};

static int proc_tgid_base_readdir(struct file * filp,
                             void * dirent, filldir_t filldir)
{
        return proc_pident_readdir(filp,dirent,filldir,
                                   tgid_base_stuff,ARRAY_SIZE(tgid_base_stuff));
}

static const struct file_operations proc_tgid_base_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_tgid_base_readdir,
};

static struct dentry *proc_tgid_base_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd){
        return proc_pident_lookup(dir, dentry,
                                  tgid_base_stuff, ARRAY_SIZE(tgid_base_stuff));
}

static const struct inode_operations proc_tgid_base_inode_operations = {
        .lookup         = proc_tgid_base_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
};

/**
 * proc_flush_task -  Remove dcache entries for @task from the /proc dcache.
 *
 * @task: task that should be flushed.
 *
 * Looks in the dcache for
 * /proc/@pid
 * /proc/@tgid/task/@pid
 * if either directory is present flushes it and all of it'ts children
 * from the dcache.
 *
 * It is safe and reasonable to cache /proc entries for a task until
 * that task exits.  After that they just clog up the dcache with
 * useless entries, possibly causing useful dcache entries to be
 * flushed instead.  This routine is proved to flush those useless
 * dcache entries at process exit time.
 *
 * NOTE: This routine is just an optimization so it does not guarantee
 *       that no dcache entries will exist at process exit time it
 *       just makes it very unlikely that any will persist.
 */
void proc_flush_task(struct task_struct *task)
{
        struct dentry *dentry, *leader, *dir;
        char buf[PROC_NUMBUF];
        struct qstr name;

        name.name = buf;
        name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
        dentry = d_hash_and_lookup(proc_mnt->mnt_root, &name);
        if (dentry) {
                shrink_dcache_parent(dentry);
                d_drop(dentry);
                dput(dentry);
        }

        if (thread_group_leader(task))
                goto out;

        name.name = buf;
        name.len = snprintf(buf, sizeof(buf), "%d", task->tgid);
        leader = d_hash_and_lookup(proc_mnt->mnt_root, &name);
        if (!leader)
                goto out;

        name.name = "task";
        name.len = strlen(name.name);
        dir = d_hash_and_lookup(leader, &name);
        if (!dir)
                goto out_put_leader;

        name.name = buf;
        name.len = snprintf(buf, sizeof(buf), "%d", task->pid);
        dentry = d_hash_and_lookup(dir, &name);
        if (dentry) {
                shrink_dcache_parent(dentry);
                d_drop(dentry);
                dput(dentry);
        }

        dput(dir);
out_put_leader:
        dput(leader);
out:
        return;
}

static struct dentry *proc_pid_instantiate(struct inode *dir,
                                           struct dentry * dentry,
                                           struct task_struct *task, const void *ptr)
{
        struct dentry *error = ERR_PTR(-ENOENT);
        struct inode *inode;

        inode = proc_pid_make_inode(dir->i_sb, task);
        if (!inode)
                goto out;

        inode->i_mode = S_IFDIR|S_IRUGO|S_IXUGO;
        inode->i_op = &proc_tgid_base_inode_operations;
        inode->i_fop = &proc_tgid_base_operations;
        inode->i_flags|=S_IMMUTABLE;
        inode->i_nlink = 5;
#ifdef CONFIG_SECURITY
        inode->i_nlink += 1;
#endif

        dentry->d_op = &pid_dentry_operations;

        d_add(dentry, inode);
        /* Close the race of the process dying before we return the dentry */
        if (pid_revalidate(dentry, NULL))
                error = NULL;
out:
        return error;
}

struct dentry *proc_pid_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *nd)
{
        struct dentry *result = ERR_PTR(-ENOENT);
        struct task_struct *task;
        unsigned tgid;

        result = proc_base_lookup(dir, dentry);
        if (!IS_ERR(result) || PTR_ERR(result) != -ENOENT)
                goto out;

        tgid = name_to_int(dentry);
        if (tgid == ~0U)
                goto out;

        rcu_read_lock();
        task = find_task_by_pid(tgid);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();
        if (!task)
                goto out;

        result = proc_pid_instantiate(dir, dentry, task, NULL);
        put_task_struct(task);
out:
        return result;
}

/*
 * Find the first task with tgid >= tgid
 *
 */
static struct task_struct *next_tgid(unsigned int tgid)
{
        struct task_struct *task;
        struct pid *pid;

        rcu_read_lock();
retry:
        task = NULL;
        pid = find_ge_pid(tgid);
        if (pid) {
                tgid = pid->nr + 1;
                task = pid_task(pid, PIDTYPE_PID);
                /* What we to know is if the pid we have find is the
                 * pid of a thread_group_leader.  Testing for task
                 * being a thread_group_leader is the obvious thing
                 * todo but there is a window when it fails, due to
                 * the pid transfer logic in de_thread.
                 *
                 * So we perform the straight forward test of seeing
                 * if the pid we have found is the pid of a thread
                 * group leader, and don't worry if the task we have
                 * found doesn't happen to be a thread group leader.
                 * As we don't care in the case of readdir.
                 */
                if (!task || !has_group_leader_pid(task))
                        goto retry;
                get_task_struct(task);
        }
        rcu_read_unlock();
        return task;
}

#define TGID_OFFSET (FIRST_PROCESS_ENTRY + ARRAY_SIZE(proc_base_stuff))

static int proc_pid_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
        struct task_struct *task, int tgid)
{
        char name[PROC_NUMBUF];
        int len = snprintf(name, sizeof(name), "%d", tgid);
        return proc_fill_cache(filp, dirent, filldir, name, len,
                                proc_pid_instantiate, task, NULL);
}

/* for the /proc/ directory itself, after non-process stuff has been done */
int proc_pid_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
        unsigned int nr = filp->f_pos - FIRST_PROCESS_ENTRY;
        struct task_struct *reaper = get_proc_task(filp->f_path.dentry->d_inode);
        struct task_struct *task;
        int tgid;

        if (!reaper)
                goto out_no_task;

        for (; nr < ARRAY_SIZE(proc_base_stuff); filp->f_pos++, nr++) {
                const struct pid_entry *p = &proc_base_stuff[nr];
                if (proc_base_fill_cache(filp, dirent, filldir, reaper, p) < 0)
                        goto out;
        }

        tgid = filp->f_pos - TGID_OFFSET;
        for (task = next_tgid(tgid);
             task;
             put_task_struct(task), task = next_tgid(tgid + 1)) {
                tgid = task->pid;
                filp->f_pos = tgid + TGID_OFFSET;
                if (proc_pid_fill_cache(filp, dirent, filldir, task, tgid) < 0) {
                        put_task_struct(task);
                        goto out;
                }
        }
        filp->f_pos = PID_MAX_LIMIT + TGID_OFFSET;
out:
        put_task_struct(reaper);
out_no_task:
        return 0;
}

/*
 * Tasks
 */
static const struct pid_entry tid_base_stuff[] = {
        DIR("fd",        S_IRUSR|S_IXUSR, fd),
        DIR("fdinfo",    S_IRUSR|S_IXUSR, fdinfo),
        REG("environ",   S_IRUSR, environ),
        INF("auxv",      S_IRUSR, pid_auxv),
        INF("status",    S_IRUGO, pid_status),
#ifdef CONFIG_SCHED_DEBUG
        REG("sched",     S_IRUGO|S_IWUSR, pid_sched),
#endif
        INF("cmdline",   S_IRUGO, pid_cmdline),
        INF("stat",      S_IRUGO, tid_stat),
        INF("statm",     S_IRUGO, pid_statm),
        REG("maps",      S_IRUGO, maps),
#ifdef CONFIG_NUMA
        REG("numa_maps", S_IRUGO, numa_maps),
#endif
        REG("mem",       S_IRUSR|S_IWUSR, mem),
        LNK("cwd",       cwd),
        LNK("root",      root),
        LNK("exe",       exe),
        REG("mounts",    S_IRUGO, mounts),
#ifdef CONFIG_MMU
        REG("clear_refs", S_IWUSR, clear_refs),
        REG("smaps",     S_IRUGO, smaps),
#endif
#ifdef CONFIG_SECURITY
        DIR("attr",      S_IRUGO|S_IXUGO, attr_dir),
#endif
#ifdef CONFIG_KALLSYMS
        INF("wchan",     S_IRUGO, pid_wchan),
#endif
#ifdef CONFIG_SCHEDSTATS
        INF("schedstat", S_IRUGO, pid_schedstat),
#endif
#ifdef CONFIG_CPUSETS
        REG("cpuset",    S_IRUGO, cpuset),
#endif
        INF("oom_score", S_IRUGO, oom_score),
        REG("oom_adj",   S_IRUGO|S_IWUSR, oom_adjust),
#ifdef CONFIG_AUDITSYSCALL
        REG("loginuid",  S_IWUSR|S_IRUGO, loginuid),
#endif
#ifdef CONFIG_FAULT_INJECTION
        REG("make-it-fail", S_IRUGO|S_IWUSR, fault_inject),
#endif
};

static int proc_tid_base_readdir(struct file * filp,
                             void * dirent, filldir_t filldir)
{
        return proc_pident_readdir(filp,dirent,filldir,
                                   tid_base_stuff,ARRAY_SIZE(tid_base_stuff));
}

static struct dentry *proc_tid_base_lookup(struct inode *dir, struct dentry *dentry, struct nameidata *nd){
        return proc_pident_lookup(dir, dentry,
                                  tid_base_stuff, ARRAY_SIZE(tid_base_stuff));
}

static const struct file_operations proc_tid_base_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_tid_base_readdir,
};

static const struct inode_operations proc_tid_base_inode_operations = {
        .lookup         = proc_tid_base_lookup,
        .getattr        = pid_getattr,
        .setattr        = proc_setattr,
};

static struct dentry *proc_task_instantiate(struct inode *dir,
        struct dentry *dentry, struct task_struct *task, const void *ptr)
{
        struct dentry *error = ERR_PTR(-ENOENT);
        struct inode *inode;
        inode = proc_pid_make_inode(dir->i_sb, task);

        if (!inode)
                goto out;
        inode->i_mode = S_IFDIR|S_IRUGO|S_IXUGO;
        inode->i_op = &proc_tid_base_inode_operations;
        inode->i_fop = &proc_tid_base_operations;
        inode->i_flags|=S_IMMUTABLE;
        inode->i_nlink = 4;
#ifdef CONFIG_SECURITY
        inode->i_nlink += 1;
#endif

        dentry->d_op = &pid_dentry_operations;

        d_add(dentry, inode);
        /* Close the race of the process dying before we return the dentry */
        if (pid_revalidate(dentry, NULL))
                error = NULL;
out:
        return error;
}

static struct dentry *proc_task_lookup(struct inode *dir, struct dentry * dentry, struct nameidata *nd)
{
        struct dentry *result = ERR_PTR(-ENOENT);
        struct task_struct *task;
        struct task_struct *leader = get_proc_task(dir);
        unsigned tid;

        if (!leader)
                goto out_no_task;

        tid = name_to_int(dentry);
        if (tid == ~0U)
                goto out;

        rcu_read_lock();
        task = find_task_by_pid(tid);
        if (task)
                get_task_struct(task);
        rcu_read_unlock();
        if (!task)
                goto out;
        if (leader->tgid != task->tgid)
                goto out_drop_task;

        result = proc_task_instantiate(dir, dentry, task, NULL);
out_drop_task:
        put_task_struct(task);
out:
        put_task_struct(leader);
out_no_task:
        return result;
}

/*
 * Find the first tid of a thread group to return to user space.
 *
 * Usually this is just the thread group leader, but if the users
 * buffer was too small or there was a seek into the middle of the
 * directory we have more work todo.
 *
 * In the case of a short read we start with find_task_by_pid.
 *
 * In the case of a seek we start with the leader and walk nr
 * threads past it.
 */
static struct task_struct *first_tid(struct task_struct *leader,
                                        int tid, int nr)
{
        struct task_struct *pos;

        rcu_read_lock();
        /* Attempt to start with the pid of a thread */
        if (tid && (nr > 0)) {
                pos = find_task_by_pid(tid);
                if (pos && (pos->group_leader == leader))
                        goto found;
        }

        /* If nr exceeds the number of threads there is nothing todo */
        pos = NULL;
        if (nr && nr >= get_nr_threads(leader))
                goto out;

        /* If we haven't found our starting place yet start
         * with the leader and walk nr threads forward.
         */
        for (pos = leader; nr > 0; --nr) {
                pos = next_thread(pos);
                if (pos == leader) {
                        pos = NULL;
                        goto out;
                }
        }
found:
        get_task_struct(pos);
out:
        rcu_read_unlock();
        return pos;
}

/*
 * Find the next thread in the thread list.
 * Return NULL if there is an error or no next thread.
 *
 * The reference to the input task_struct is released.
 */
static struct task_struct *next_tid(struct task_struct *start)
{
        struct task_struct *pos = NULL;
        rcu_read_lock();
        if (pid_alive(start)) {
                pos = next_thread(start);
                if (thread_group_leader(pos))
                        pos = NULL;
                else
                        get_task_struct(pos);
        }
        rcu_read_unlock();
        put_task_struct(start);
        return pos;
}

static int proc_task_fill_cache(struct file *filp, void *dirent, filldir_t filldir,
        struct task_struct *task, int tid)
{
        char name[PROC_NUMBUF];
        int len = snprintf(name, sizeof(name), "%d", tid);
        return proc_fill_cache(filp, dirent, filldir, name, len,
                                proc_task_instantiate, task, NULL);
}

/* for the /proc/TGID/task/ directories */
static int proc_task_readdir(struct file * filp, void * dirent, filldir_t filldir)
{
        struct dentry *dentry = filp->f_path.dentry;
        struct inode *inode = dentry->d_inode;
        struct task_struct *leader = NULL;
        struct task_struct *task;
        int retval = -ENOENT;
        ino_t ino;
        int tid;
        unsigned long pos = filp->f_pos;  /* avoiding "long long" filp->f_pos */

        task = get_proc_task(inode);
        if (!task)
                goto out_no_task;
        rcu_read_lock();
        if (pid_alive(task)) {
                leader = task->group_leader;
                get_task_struct(leader);
        }
        rcu_read_unlock();
        put_task_struct(task);
        if (!leader)
                goto out_no_task;
        retval = 0;

        switch (pos) {
        case 0:
                ino = inode->i_ino;
                if (filldir(dirent, ".", 1, pos, ino, DT_DIR) < 0)
                        goto out;
                pos++;
                /* fall through */
        case 1:
                ino = parent_ino(dentry);
                if (filldir(dirent, "..", 2, pos, ino, DT_DIR) < 0)
                        goto out;
                pos++;
                /* fall through */
        }

        /* f_version caches the tgid value that the last readdir call couldn't
         * return. lseek aka telldir automagically resets f_version to 0.
         */
        tid = (int)filp->f_version;
        filp->f_version = 0;
        for (task = first_tid(leader, tid, pos - 2);
             task;
             task = next_tid(task), pos++) {
                tid = task->pid;
                if (proc_task_fill_cache(filp, dirent, filldir, task, tid) < 0) {
                        /* returning this tgid failed, save it as the first
                         * pid for the next readir call */
                        filp->f_version = (u64)tid;
                        put_task_struct(task);
                        break;
                }
        }
out:
        filp->f_pos = pos;
        put_task_struct(leader);
out_no_task:
        return retval;
}

static int proc_task_getattr(struct vfsmount *mnt, struct dentry *dentry, struct kstat *stat)
{
        struct inode *inode = dentry->d_inode;
        struct task_struct *p = get_proc_task(inode);
        generic_fillattr(inode, stat);

        if (p) {
                rcu_read_lock();
                stat->nlink += get_nr_threads(p);
                rcu_read_unlock();
                put_task_struct(p);
        }

        return 0;
}

static const struct inode_operations proc_task_inode_operations = {
        .lookup         = proc_task_lookup,
        .getattr        = proc_task_getattr,
        .setattr        = proc_setattr,
};

static const struct file_operations proc_task_operations = {
        .read           = generic_read_dir,
        .readdir        = proc_task_readdir,
};