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![Eric W. Biederman](/assets/img/avatar_default.png)
Modify the request_module to prefix the file system type with "fs-" and add aliases to all of the filesystems that can be built as modules to match. A common practice is to build all of the kernel code and leave code that is not commonly needed as modules, with the result that many users are exposed to any bug anywhere in the kernel. Looking for filesystems with a fs- prefix limits the pool of possible modules that can be loaded by mount to just filesystems trivially making things safer with no real cost. Using aliases means user space can control the policy of which filesystem modules are auto-loaded by editing /etc/modprobe.d/*.conf with blacklist and alias directives. Allowing simple, safe, well understood work-arounds to known problematic software. This also addresses a rare but unfortunate problem where the filesystem name is not the same as it's module name and module auto-loading would not work. While writing this patch I saw a handful of such cases. The most significant being autofs that lives in the module autofs4. This is relevant to user namespaces because we can reach the request module in get_fs_type() without having any special permissions, and people get uncomfortable when a user specified string (in this case the filesystem type) goes all of the way to request_module. After having looked at this issue I don't think there is any particular reason to perform any filtering or permission checks beyond making it clear in the module request that we want a filesystem module. The common pattern in the kernel is to call request_module() without regards to the users permissions. In general all a filesystem module does once loaded is call register_filesystem() and go to sleep. Which means there is not much attack surface exposed by loading a filesytem module unless the filesystem is mounted. In a user namespace filesystems are not mounted unless .fs_flags = FS_USERNS_MOUNT, which most filesystems do not set today. Acked-by: Serge Hallyn <serge.hallyn@canonical.com> Acked-by: Kees Cook <keescook@chromium.org> Reported-by: Kees Cook <keescook@google.com> Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
477 lines
9.7 KiB
C
477 lines
9.7 KiB
C
/* inode.c: /proc/openprom handling routines
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*
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* Copyright (C) 1996-1999 Jakub Jelinek (jakub@redhat.com)
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* Copyright (C) 1998 Eddie C. Dost (ecd@skynet.be)
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*/
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#include <linux/module.h>
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#include <linux/types.h>
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#include <linux/string.h>
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/slab.h>
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#include <linux/seq_file.h>
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#include <linux/magic.h>
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#include <asm/openprom.h>
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#include <asm/oplib.h>
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#include <asm/prom.h>
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#include <asm/uaccess.h>
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static DEFINE_MUTEX(op_mutex);
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#define OPENPROM_ROOT_INO 0
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enum op_inode_type {
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op_inode_node,
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op_inode_prop,
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};
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union op_inode_data {
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struct device_node *node;
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struct property *prop;
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};
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struct op_inode_info {
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struct inode vfs_inode;
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enum op_inode_type type;
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union op_inode_data u;
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};
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static struct inode *openprom_iget(struct super_block *sb, ino_t ino);
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static inline struct op_inode_info *OP_I(struct inode *inode)
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{
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return container_of(inode, struct op_inode_info, vfs_inode);
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}
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static int is_string(unsigned char *p, int len)
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{
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int i;
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for (i = 0; i < len; i++) {
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unsigned char val = p[i];
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if ((i && !val) ||
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(val >= ' ' && val <= '~'))
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continue;
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return 0;
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}
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return 1;
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}
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static int property_show(struct seq_file *f, void *v)
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{
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struct property *prop = f->private;
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void *pval;
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int len;
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len = prop->length;
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pval = prop->value;
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if (is_string(pval, len)) {
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while (len > 0) {
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int n = strlen(pval);
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seq_printf(f, "%s", (char *) pval);
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/* Skip over the NULL byte too. */
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pval += n + 1;
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len -= n + 1;
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if (len > 0)
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seq_printf(f, " + ");
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}
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} else {
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if (len & 3) {
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while (len) {
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len--;
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if (len)
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seq_printf(f, "%02x.",
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*(unsigned char *) pval);
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else
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seq_printf(f, "%02x",
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*(unsigned char *) pval);
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pval++;
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}
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} else {
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while (len >= 4) {
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len -= 4;
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if (len)
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seq_printf(f, "%08x.",
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*(unsigned int *) pval);
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else
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seq_printf(f, "%08x",
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*(unsigned int *) pval);
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pval += 4;
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}
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}
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}
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seq_printf(f, "\n");
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return 0;
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}
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static void *property_start(struct seq_file *f, loff_t *pos)
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{
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if (*pos == 0)
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return pos;
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return NULL;
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}
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static void *property_next(struct seq_file *f, void *v, loff_t *pos)
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{
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(*pos)++;
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return NULL;
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}
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static void property_stop(struct seq_file *f, void *v)
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{
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/* Nothing to do */
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}
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static const struct seq_operations property_op = {
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.start = property_start,
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.next = property_next,
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.stop = property_stop,
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.show = property_show
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};
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static int property_open(struct inode *inode, struct file *file)
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{
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struct op_inode_info *oi = OP_I(inode);
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int ret;
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BUG_ON(oi->type != op_inode_prop);
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ret = seq_open(file, &property_op);
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if (!ret) {
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struct seq_file *m = file->private_data;
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m->private = oi->u.prop;
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}
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return ret;
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}
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static const struct file_operations openpromfs_prop_ops = {
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.open = property_open,
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.read = seq_read,
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.llseek = seq_lseek,
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.release = seq_release,
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};
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static int openpromfs_readdir(struct file *, void *, filldir_t);
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static const struct file_operations openprom_operations = {
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.read = generic_read_dir,
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.readdir = openpromfs_readdir,
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.llseek = generic_file_llseek,
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};
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static struct dentry *openpromfs_lookup(struct inode *, struct dentry *, unsigned int);
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static const struct inode_operations openprom_inode_operations = {
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.lookup = openpromfs_lookup,
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};
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static struct dentry *openpromfs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
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{
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struct op_inode_info *ent_oi, *oi = OP_I(dir);
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struct device_node *dp, *child;
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struct property *prop;
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enum op_inode_type ent_type;
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union op_inode_data ent_data;
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const char *name;
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struct inode *inode;
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unsigned int ino;
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int len;
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BUG_ON(oi->type != op_inode_node);
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dp = oi->u.node;
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name = dentry->d_name.name;
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len = dentry->d_name.len;
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mutex_lock(&op_mutex);
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child = dp->child;
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while (child) {
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int n = strlen(child->path_component_name);
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if (len == n &&
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!strncmp(child->path_component_name, name, len)) {
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ent_type = op_inode_node;
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ent_data.node = child;
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ino = child->unique_id;
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goto found;
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}
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child = child->sibling;
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}
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prop = dp->properties;
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while (prop) {
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int n = strlen(prop->name);
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if (len == n && !strncmp(prop->name, name, len)) {
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ent_type = op_inode_prop;
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ent_data.prop = prop;
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ino = prop->unique_id;
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goto found;
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}
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prop = prop->next;
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}
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mutex_unlock(&op_mutex);
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return ERR_PTR(-ENOENT);
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found:
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inode = openprom_iget(dir->i_sb, ino);
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mutex_unlock(&op_mutex);
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if (IS_ERR(inode))
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return ERR_CAST(inode);
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ent_oi = OP_I(inode);
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ent_oi->type = ent_type;
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ent_oi->u = ent_data;
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switch (ent_type) {
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case op_inode_node:
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inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO;
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inode->i_op = &openprom_inode_operations;
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inode->i_fop = &openprom_operations;
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set_nlink(inode, 2);
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break;
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case op_inode_prop:
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if (!strcmp(dp->name, "options") && (len == 17) &&
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!strncmp (name, "security-password", 17))
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inode->i_mode = S_IFREG | S_IRUSR | S_IWUSR;
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else
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inode->i_mode = S_IFREG | S_IRUGO;
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inode->i_fop = &openpromfs_prop_ops;
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set_nlink(inode, 1);
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inode->i_size = ent_oi->u.prop->length;
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break;
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}
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d_add(dentry, inode);
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return NULL;
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}
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static int openpromfs_readdir(struct file * filp, void * dirent, filldir_t filldir)
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{
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struct inode *inode = file_inode(filp);
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struct op_inode_info *oi = OP_I(inode);
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struct device_node *dp = oi->u.node;
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struct device_node *child;
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struct property *prop;
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unsigned int ino;
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int i;
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mutex_lock(&op_mutex);
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ino = inode->i_ino;
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i = filp->f_pos;
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switch (i) {
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case 0:
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if (filldir(dirent, ".", 1, i, ino, DT_DIR) < 0)
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goto out;
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i++;
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filp->f_pos++;
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/* fall thru */
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case 1:
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if (filldir(dirent, "..", 2, i,
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(dp->parent == NULL ?
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OPENPROM_ROOT_INO :
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dp->parent->unique_id), DT_DIR) < 0)
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goto out;
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i++;
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filp->f_pos++;
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/* fall thru */
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default:
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i -= 2;
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/* First, the children nodes as directories. */
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child = dp->child;
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while (i && child) {
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child = child->sibling;
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i--;
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}
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while (child) {
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if (filldir(dirent,
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child->path_component_name,
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strlen(child->path_component_name),
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filp->f_pos, child->unique_id, DT_DIR) < 0)
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goto out;
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filp->f_pos++;
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child = child->sibling;
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}
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/* Next, the properties as files. */
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prop = dp->properties;
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while (i && prop) {
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prop = prop->next;
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i--;
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}
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while (prop) {
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if (filldir(dirent, prop->name, strlen(prop->name),
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filp->f_pos, prop->unique_id, DT_REG) < 0)
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goto out;
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filp->f_pos++;
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prop = prop->next;
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}
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}
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out:
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mutex_unlock(&op_mutex);
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return 0;
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}
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static struct kmem_cache *op_inode_cachep;
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static struct inode *openprom_alloc_inode(struct super_block *sb)
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{
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struct op_inode_info *oi;
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oi = kmem_cache_alloc(op_inode_cachep, GFP_KERNEL);
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if (!oi)
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return NULL;
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return &oi->vfs_inode;
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}
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static void openprom_i_callback(struct rcu_head *head)
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{
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struct inode *inode = container_of(head, struct inode, i_rcu);
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kmem_cache_free(op_inode_cachep, OP_I(inode));
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}
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static void openprom_destroy_inode(struct inode *inode)
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{
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call_rcu(&inode->i_rcu, openprom_i_callback);
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}
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static struct inode *openprom_iget(struct super_block *sb, ino_t ino)
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{
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struct inode *inode;
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inode = iget_locked(sb, ino);
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if (!inode)
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return ERR_PTR(-ENOMEM);
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if (inode->i_state & I_NEW) {
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inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
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if (inode->i_ino == OPENPROM_ROOT_INO) {
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inode->i_op = &openprom_inode_operations;
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inode->i_fop = &openprom_operations;
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inode->i_mode = S_IFDIR | S_IRUGO | S_IXUGO;
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}
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unlock_new_inode(inode);
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}
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return inode;
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}
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static int openprom_remount(struct super_block *sb, int *flags, char *data)
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{
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*flags |= MS_NOATIME;
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return 0;
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}
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static const struct super_operations openprom_sops = {
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.alloc_inode = openprom_alloc_inode,
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.destroy_inode = openprom_destroy_inode,
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.statfs = simple_statfs,
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.remount_fs = openprom_remount,
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};
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static int openprom_fill_super(struct super_block *s, void *data, int silent)
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{
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struct inode *root_inode;
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struct op_inode_info *oi;
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int ret;
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s->s_flags |= MS_NOATIME;
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s->s_blocksize = 1024;
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s->s_blocksize_bits = 10;
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s->s_magic = OPENPROM_SUPER_MAGIC;
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s->s_op = &openprom_sops;
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s->s_time_gran = 1;
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root_inode = openprom_iget(s, OPENPROM_ROOT_INO);
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if (IS_ERR(root_inode)) {
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ret = PTR_ERR(root_inode);
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goto out_no_root;
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}
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oi = OP_I(root_inode);
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oi->type = op_inode_node;
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oi->u.node = of_find_node_by_path("/");
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s->s_root = d_make_root(root_inode);
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if (!s->s_root)
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goto out_no_root_dentry;
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return 0;
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out_no_root_dentry:
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ret = -ENOMEM;
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out_no_root:
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printk("openprom_fill_super: get root inode failed\n");
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return ret;
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}
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static struct dentry *openprom_mount(struct file_system_type *fs_type,
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int flags, const char *dev_name, void *data)
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{
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return mount_single(fs_type, flags, data, openprom_fill_super);
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}
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static struct file_system_type openprom_fs_type = {
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.owner = THIS_MODULE,
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.name = "openpromfs",
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.mount = openprom_mount,
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.kill_sb = kill_anon_super,
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};
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MODULE_ALIAS_FS("openpromfs");
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static void op_inode_init_once(void *data)
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{
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struct op_inode_info *oi = (struct op_inode_info *) data;
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inode_init_once(&oi->vfs_inode);
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}
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static int __init init_openprom_fs(void)
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{
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int err;
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op_inode_cachep = kmem_cache_create("op_inode_cache",
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sizeof(struct op_inode_info),
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0,
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(SLAB_RECLAIM_ACCOUNT |
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SLAB_MEM_SPREAD),
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op_inode_init_once);
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if (!op_inode_cachep)
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return -ENOMEM;
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err = register_filesystem(&openprom_fs_type);
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if (err)
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kmem_cache_destroy(op_inode_cachep);
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return err;
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}
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static void __exit exit_openprom_fs(void)
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{
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unregister_filesystem(&openprom_fs_type);
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/*
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* Make sure all delayed rcu free inodes are flushed before we
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* destroy cache.
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*/
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rcu_barrier();
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kmem_cache_destroy(op_inode_cachep);
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}
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module_init(init_openprom_fs)
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module_exit(exit_openprom_fs)
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MODULE_LICENSE("GPL");
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