330 lines
6.4 KiB
C
330 lines
6.4 KiB
C
/*
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* dcookies.c
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*
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* Copyright 2002 John Levon <levon@movementarian.org>
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*
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* Persistent cookie-path mappings. These are used by
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* profilers to convert a per-task EIP value into something
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* non-transitory that can be processed at a later date.
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* This is done by locking the dentry/vfsmnt pair in the
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* kernel until released by the tasks needing the persistent
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* objects. The tag is simply an unsigned long that refers
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* to the pair and can be looked up from userspace.
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*/
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#include <linux/syscalls.h>
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#include <linux/module.h>
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#include <linux/slab.h>
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#include <linux/list.h>
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#include <linux/mount.h>
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#include <linux/capability.h>
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#include <linux/dcache.h>
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#include <linux/mm.h>
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#include <linux/errno.h>
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#include <linux/dcookies.h>
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#include <linux/mutex.h>
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#include <asm/uaccess.h>
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/* The dcookies are allocated from a kmem_cache and
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* hashed onto a small number of lists. None of the
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* code here is particularly performance critical
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*/
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struct dcookie_struct {
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struct dentry * dentry;
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struct vfsmount * vfsmnt;
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struct list_head hash_list;
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};
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static LIST_HEAD(dcookie_users);
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static DEFINE_MUTEX(dcookie_mutex);
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static struct kmem_cache *dcookie_cache __read_mostly;
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static struct list_head *dcookie_hashtable __read_mostly;
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static size_t hash_size __read_mostly;
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static inline int is_live(void)
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{
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return !(list_empty(&dcookie_users));
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}
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/* The dentry is locked, its address will do for the cookie */
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static inline unsigned long dcookie_value(struct dcookie_struct * dcs)
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{
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return (unsigned long)dcs->dentry;
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}
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static size_t dcookie_hash(unsigned long dcookie)
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{
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return (dcookie >> L1_CACHE_SHIFT) & (hash_size - 1);
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}
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static struct dcookie_struct * find_dcookie(unsigned long dcookie)
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{
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struct dcookie_struct *found = NULL;
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struct dcookie_struct * dcs;
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struct list_head * pos;
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struct list_head * list;
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list = dcookie_hashtable + dcookie_hash(dcookie);
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list_for_each(pos, list) {
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dcs = list_entry(pos, struct dcookie_struct, hash_list);
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if (dcookie_value(dcs) == dcookie) {
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found = dcs;
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break;
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}
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}
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return found;
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}
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static void hash_dcookie(struct dcookie_struct * dcs)
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{
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struct list_head * list = dcookie_hashtable + dcookie_hash(dcookie_value(dcs));
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list_add(&dcs->hash_list, list);
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}
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static struct dcookie_struct * alloc_dcookie(struct dentry * dentry,
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struct vfsmount * vfsmnt)
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{
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struct dcookie_struct * dcs = kmem_cache_alloc(dcookie_cache, GFP_KERNEL);
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if (!dcs)
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return NULL;
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dentry->d_cookie = dcs;
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dcs->dentry = dget(dentry);
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dcs->vfsmnt = mntget(vfsmnt);
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hash_dcookie(dcs);
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return dcs;
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}
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/* This is the main kernel-side routine that retrieves the cookie
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* value for a dentry/vfsmnt pair.
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*/
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int get_dcookie(struct dentry * dentry, struct vfsmount * vfsmnt,
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unsigned long * cookie)
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{
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int err = 0;
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struct dcookie_struct * dcs;
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mutex_lock(&dcookie_mutex);
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if (!is_live()) {
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err = -EINVAL;
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goto out;
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}
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dcs = dentry->d_cookie;
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if (!dcs)
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dcs = alloc_dcookie(dentry, vfsmnt);
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if (!dcs) {
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err = -ENOMEM;
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goto out;
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}
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*cookie = dcookie_value(dcs);
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out:
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mutex_unlock(&dcookie_mutex);
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return err;
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}
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/* And here is where the userspace process can look up the cookie value
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* to retrieve the path.
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*/
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asmlinkage long sys_lookup_dcookie(u64 cookie64, char __user * buf, size_t len)
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{
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unsigned long cookie = (unsigned long)cookie64;
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int err = -EINVAL;
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char * kbuf;
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char * path;
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size_t pathlen;
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struct dcookie_struct * dcs;
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/* we could leak path information to users
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* without dir read permission without this
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*/
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if (!capable(CAP_SYS_ADMIN))
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return -EPERM;
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mutex_lock(&dcookie_mutex);
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if (!is_live()) {
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err = -EINVAL;
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goto out;
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}
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if (!(dcs = find_dcookie(cookie)))
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goto out;
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err = -ENOMEM;
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kbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
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if (!kbuf)
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goto out;
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/* FIXME: (deleted) ? */
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path = d_path(dcs->dentry, dcs->vfsmnt, kbuf, PAGE_SIZE);
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if (IS_ERR(path)) {
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err = PTR_ERR(path);
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goto out_free;
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}
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err = -ERANGE;
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pathlen = kbuf + PAGE_SIZE - path;
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if (pathlen <= len) {
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err = pathlen;
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if (copy_to_user(buf, path, pathlen))
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err = -EFAULT;
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}
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out_free:
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kfree(kbuf);
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out:
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mutex_unlock(&dcookie_mutex);
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return err;
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}
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static int dcookie_init(void)
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{
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struct list_head * d;
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unsigned int i, hash_bits;
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int err = -ENOMEM;
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dcookie_cache = kmem_cache_create("dcookie_cache",
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sizeof(struct dcookie_struct),
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0, 0, NULL, NULL);
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if (!dcookie_cache)
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goto out;
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dcookie_hashtable = kmalloc(PAGE_SIZE, GFP_KERNEL);
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if (!dcookie_hashtable)
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goto out_kmem;
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err = 0;
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/*
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* Find the power-of-two list-heads that can fit into the allocation..
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* We don't guarantee that "sizeof(struct list_head)" is necessarily
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* a power-of-two.
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*/
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hash_size = PAGE_SIZE / sizeof(struct list_head);
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hash_bits = 0;
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do {
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hash_bits++;
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} while ((hash_size >> hash_bits) != 0);
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hash_bits--;
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/*
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* Re-calculate the actual number of entries and the mask
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* from the number of bits we can fit.
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*/
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hash_size = 1UL << hash_bits;
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/* And initialize the newly allocated array */
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d = dcookie_hashtable;
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i = hash_size;
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do {
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INIT_LIST_HEAD(d);
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d++;
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i--;
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} while (i);
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out:
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return err;
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out_kmem:
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kmem_cache_destroy(dcookie_cache);
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goto out;
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}
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static void free_dcookie(struct dcookie_struct * dcs)
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{
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dcs->dentry->d_cookie = NULL;
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dput(dcs->dentry);
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mntput(dcs->vfsmnt);
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kmem_cache_free(dcookie_cache, dcs);
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}
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static void dcookie_exit(void)
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{
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struct list_head * list;
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struct list_head * pos;
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struct list_head * pos2;
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struct dcookie_struct * dcs;
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size_t i;
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for (i = 0; i < hash_size; ++i) {
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list = dcookie_hashtable + i;
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list_for_each_safe(pos, pos2, list) {
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dcs = list_entry(pos, struct dcookie_struct, hash_list);
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list_del(&dcs->hash_list);
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free_dcookie(dcs);
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}
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}
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kfree(dcookie_hashtable);
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kmem_cache_destroy(dcookie_cache);
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}
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struct dcookie_user {
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struct list_head next;
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};
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struct dcookie_user * dcookie_register(void)
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{
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struct dcookie_user * user;
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mutex_lock(&dcookie_mutex);
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user = kmalloc(sizeof(struct dcookie_user), GFP_KERNEL);
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if (!user)
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goto out;
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if (!is_live() && dcookie_init())
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goto out_free;
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list_add(&user->next, &dcookie_users);
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out:
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mutex_unlock(&dcookie_mutex);
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return user;
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out_free:
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kfree(user);
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user = NULL;
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goto out;
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}
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void dcookie_unregister(struct dcookie_user * user)
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{
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mutex_lock(&dcookie_mutex);
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list_del(&user->next);
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kfree(user);
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if (!is_live())
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dcookie_exit();
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mutex_unlock(&dcookie_mutex);
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}
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EXPORT_SYMBOL_GPL(dcookie_register);
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EXPORT_SYMBOL_GPL(dcookie_unregister);
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EXPORT_SYMBOL_GPL(get_dcookie);
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