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![Christian Brauner](/assets/img/avatar_default.png)
The various vfs_*() helpers are called by filesystems or by the vfs itself to perform core operations such as create, link, mkdir, mknod, rename, rmdir, tmpfile and unlink. Enable them to handle idmapped mounts. If the inode is accessed through an idmapped mount map it into the mount's user namespace and pass it down. Afterwards the checks and operations are identical to non-idmapped mounts. If the initial user namespace is passed nothing changes so non-idmapped mounts will see identical behavior as before. Link: https://lore.kernel.org/r/20210121131959.646623-15-christian.brauner@ubuntu.com Cc: Christoph Hellwig <hch@lst.de> Cc: David Howells <dhowells@redhat.com> Cc: Al Viro <viro@zeniv.linux.org.uk> Cc: linux-fsdevel@vger.kernel.org Reviewed-by: Christoph Hellwig <hch@lst.de> Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
479 lines
10 KiB
C
479 lines
10 KiB
C
// SPDX-License-Identifier: GPL-2.0
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/*
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* devtmpfs - kernel-maintained tmpfs-based /dev
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*
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* Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
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*
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* During bootup, before any driver core device is registered,
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* devtmpfs, a tmpfs-based filesystem is created. Every driver-core
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* device which requests a device node, will add a node in this
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* filesystem.
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* By default, all devices are named after the name of the device,
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* owned by root and have a default mode of 0600. Subsystems can
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* overwrite the default setting if needed.
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*/
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#include <linux/kernel.h>
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#include <linux/syscalls.h>
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#include <linux/mount.h>
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#include <linux/device.h>
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#include <linux/genhd.h>
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#include <linux/namei.h>
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#include <linux/fs.h>
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#include <linux/shmem_fs.h>
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#include <linux/ramfs.h>
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#include <linux/sched.h>
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#include <linux/slab.h>
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#include <linux/kthread.h>
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#include <linux/init_syscalls.h>
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#include <uapi/linux/mount.h>
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#include "base.h"
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static struct task_struct *thread;
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static int __initdata mount_dev = IS_ENABLED(CONFIG_DEVTMPFS_MOUNT);
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static DEFINE_SPINLOCK(req_lock);
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static struct req {
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struct req *next;
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struct completion done;
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int err;
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const char *name;
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umode_t mode; /* 0 => delete */
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kuid_t uid;
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kgid_t gid;
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struct device *dev;
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} *requests;
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static int __init mount_param(char *str)
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{
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mount_dev = simple_strtoul(str, NULL, 0);
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return 1;
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}
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__setup("devtmpfs.mount=", mount_param);
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static struct vfsmount *mnt;
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static struct dentry *public_dev_mount(struct file_system_type *fs_type, int flags,
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const char *dev_name, void *data)
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{
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struct super_block *s = mnt->mnt_sb;
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atomic_inc(&s->s_active);
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down_write(&s->s_umount);
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return dget(s->s_root);
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}
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static struct file_system_type internal_fs_type = {
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.name = "devtmpfs",
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#ifdef CONFIG_TMPFS
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.init_fs_context = shmem_init_fs_context,
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.parameters = shmem_fs_parameters,
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#else
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.init_fs_context = ramfs_init_fs_context,
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.parameters = ramfs_fs_parameters,
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#endif
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.kill_sb = kill_litter_super,
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};
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static struct file_system_type dev_fs_type = {
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.name = "devtmpfs",
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.mount = public_dev_mount,
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};
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#ifdef CONFIG_BLOCK
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static inline int is_blockdev(struct device *dev)
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{
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return dev->class == &block_class;
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}
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#else
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static inline int is_blockdev(struct device *dev) { return 0; }
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#endif
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static int devtmpfs_submit_req(struct req *req, const char *tmp)
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{
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init_completion(&req->done);
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spin_lock(&req_lock);
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req->next = requests;
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requests = req;
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spin_unlock(&req_lock);
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wake_up_process(thread);
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wait_for_completion(&req->done);
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kfree(tmp);
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return req->err;
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}
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int devtmpfs_create_node(struct device *dev)
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{
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const char *tmp = NULL;
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struct req req;
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if (!thread)
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return 0;
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req.mode = 0;
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req.uid = GLOBAL_ROOT_UID;
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req.gid = GLOBAL_ROOT_GID;
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req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
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if (!req.name)
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return -ENOMEM;
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if (req.mode == 0)
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req.mode = 0600;
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if (is_blockdev(dev))
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req.mode |= S_IFBLK;
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else
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req.mode |= S_IFCHR;
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req.dev = dev;
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return devtmpfs_submit_req(&req, tmp);
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}
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int devtmpfs_delete_node(struct device *dev)
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{
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const char *tmp = NULL;
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struct req req;
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if (!thread)
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return 0;
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req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
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if (!req.name)
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return -ENOMEM;
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req.mode = 0;
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req.dev = dev;
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return devtmpfs_submit_req(&req, tmp);
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}
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static int dev_mkdir(const char *name, umode_t mode)
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{
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struct dentry *dentry;
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struct path path;
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int err;
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dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
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if (IS_ERR(dentry))
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return PTR_ERR(dentry);
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err = vfs_mkdir(&init_user_ns, d_inode(path.dentry), dentry, mode);
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if (!err)
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/* mark as kernel-created inode */
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d_inode(dentry)->i_private = &thread;
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done_path_create(&path, dentry);
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return err;
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}
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static int create_path(const char *nodepath)
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{
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char *path;
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char *s;
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int err = 0;
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/* parent directories do not exist, create them */
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path = kstrdup(nodepath, GFP_KERNEL);
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if (!path)
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return -ENOMEM;
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s = path;
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for (;;) {
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s = strchr(s, '/');
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if (!s)
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break;
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s[0] = '\0';
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err = dev_mkdir(path, 0755);
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if (err && err != -EEXIST)
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break;
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s[0] = '/';
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s++;
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}
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kfree(path);
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return err;
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}
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static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
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kgid_t gid, struct device *dev)
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{
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struct dentry *dentry;
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struct path path;
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int err;
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dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
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if (dentry == ERR_PTR(-ENOENT)) {
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create_path(nodename);
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dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
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}
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if (IS_ERR(dentry))
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return PTR_ERR(dentry);
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err = vfs_mknod(&init_user_ns, d_inode(path.dentry), dentry, mode,
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dev->devt);
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if (!err) {
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struct iattr newattrs;
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newattrs.ia_mode = mode;
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newattrs.ia_uid = uid;
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newattrs.ia_gid = gid;
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newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
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inode_lock(d_inode(dentry));
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notify_change(&init_user_ns, dentry, &newattrs, NULL);
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inode_unlock(d_inode(dentry));
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/* mark as kernel-created inode */
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d_inode(dentry)->i_private = &thread;
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}
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done_path_create(&path, dentry);
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return err;
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}
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static int dev_rmdir(const char *name)
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{
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struct path parent;
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struct dentry *dentry;
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int err;
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dentry = kern_path_locked(name, &parent);
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if (IS_ERR(dentry))
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return PTR_ERR(dentry);
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if (d_really_is_positive(dentry)) {
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if (d_inode(dentry)->i_private == &thread)
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err = vfs_rmdir(&init_user_ns, d_inode(parent.dentry),
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dentry);
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else
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err = -EPERM;
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} else {
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err = -ENOENT;
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}
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dput(dentry);
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inode_unlock(d_inode(parent.dentry));
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path_put(&parent);
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return err;
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}
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static int delete_path(const char *nodepath)
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{
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char *path;
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int err = 0;
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path = kstrdup(nodepath, GFP_KERNEL);
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if (!path)
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return -ENOMEM;
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for (;;) {
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char *base;
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base = strrchr(path, '/');
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if (!base)
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break;
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base[0] = '\0';
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err = dev_rmdir(path);
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if (err)
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break;
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}
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kfree(path);
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return err;
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}
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static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
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{
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/* did we create it */
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if (inode->i_private != &thread)
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return 0;
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/* does the dev_t match */
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if (is_blockdev(dev)) {
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if (!S_ISBLK(stat->mode))
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return 0;
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} else {
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if (!S_ISCHR(stat->mode))
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return 0;
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}
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if (stat->rdev != dev->devt)
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return 0;
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/* ours */
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return 1;
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}
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static int handle_remove(const char *nodename, struct device *dev)
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{
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struct path parent;
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struct dentry *dentry;
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int deleted = 0;
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int err;
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dentry = kern_path_locked(nodename, &parent);
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if (IS_ERR(dentry))
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return PTR_ERR(dentry);
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if (d_really_is_positive(dentry)) {
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struct kstat stat;
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struct path p = {.mnt = parent.mnt, .dentry = dentry};
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err = vfs_getattr(&p, &stat, STATX_TYPE | STATX_MODE,
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AT_STATX_SYNC_AS_STAT);
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if (!err && dev_mynode(dev, d_inode(dentry), &stat)) {
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struct iattr newattrs;
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/*
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* before unlinking this node, reset permissions
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* of possible references like hardlinks
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*/
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newattrs.ia_uid = GLOBAL_ROOT_UID;
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newattrs.ia_gid = GLOBAL_ROOT_GID;
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newattrs.ia_mode = stat.mode & ~0777;
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newattrs.ia_valid =
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ATTR_UID|ATTR_GID|ATTR_MODE;
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inode_lock(d_inode(dentry));
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notify_change(&init_user_ns, dentry, &newattrs, NULL);
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inode_unlock(d_inode(dentry));
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err = vfs_unlink(&init_user_ns, d_inode(parent.dentry),
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dentry, NULL);
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if (!err || err == -ENOENT)
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deleted = 1;
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}
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} else {
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err = -ENOENT;
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}
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dput(dentry);
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inode_unlock(d_inode(parent.dentry));
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path_put(&parent);
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if (deleted && strchr(nodename, '/'))
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delete_path(nodename);
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return err;
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}
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/*
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* If configured, or requested by the commandline, devtmpfs will be
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* auto-mounted after the kernel mounted the root filesystem.
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*/
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int __init devtmpfs_mount(void)
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{
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int err;
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if (!mount_dev)
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return 0;
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if (!thread)
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return 0;
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err = init_mount("devtmpfs", "dev", "devtmpfs", MS_SILENT, NULL);
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if (err)
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printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
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else
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printk(KERN_INFO "devtmpfs: mounted\n");
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return err;
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}
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static DECLARE_COMPLETION(setup_done);
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static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
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struct device *dev)
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{
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if (mode)
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return handle_create(name, mode, uid, gid, dev);
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else
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return handle_remove(name, dev);
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}
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static void __noreturn devtmpfs_work_loop(void)
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{
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while (1) {
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spin_lock(&req_lock);
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while (requests) {
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struct req *req = requests;
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requests = NULL;
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spin_unlock(&req_lock);
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while (req) {
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struct req *next = req->next;
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req->err = handle(req->name, req->mode,
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req->uid, req->gid, req->dev);
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complete(&req->done);
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req = next;
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}
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spin_lock(&req_lock);
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}
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__set_current_state(TASK_INTERRUPTIBLE);
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spin_unlock(&req_lock);
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schedule();
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}
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}
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static int __init devtmpfs_setup(void *p)
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{
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int err;
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err = ksys_unshare(CLONE_NEWNS);
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if (err)
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goto out;
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err = init_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, NULL);
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if (err)
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goto out;
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init_chdir("/.."); /* will traverse into overmounted root */
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init_chroot(".");
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out:
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*(int *)p = err;
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complete(&setup_done);
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return err;
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}
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/*
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* The __ref is because devtmpfs_setup needs to be __init for the routines it
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* calls. That call is done while devtmpfs_init, which is marked __init,
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* synchronously waits for it to complete.
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*/
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static int __ref devtmpfsd(void *p)
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{
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int err = devtmpfs_setup(p);
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if (err)
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return err;
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devtmpfs_work_loop();
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return 0;
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}
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/*
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* Create devtmpfs instance, driver-core devices will add their device
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* nodes here.
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*/
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int __init devtmpfs_init(void)
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{
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char opts[] = "mode=0755";
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int err;
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mnt = vfs_kern_mount(&internal_fs_type, 0, "devtmpfs", opts);
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if (IS_ERR(mnt)) {
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printk(KERN_ERR "devtmpfs: unable to create devtmpfs %ld\n",
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PTR_ERR(mnt));
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return PTR_ERR(mnt);
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}
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err = register_filesystem(&dev_fs_type);
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if (err) {
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printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
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"type %i\n", err);
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return err;
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}
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thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
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if (!IS_ERR(thread)) {
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wait_for_completion(&setup_done);
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} else {
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err = PTR_ERR(thread);
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thread = NULL;
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}
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if (err) {
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printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
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unregister_filesystem(&dev_fs_type);
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return err;
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}
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printk(KERN_INFO "devtmpfs: initialized\n");
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return 0;
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}
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