// SPDX-License-Identifier: GPL-2.0-only /* * CUSE: Character device in Userspace * * Copyright (C) 2008-2009 SUSE Linux Products GmbH * Copyright (C) 2008-2009 Tejun Heo <[email protected]> * * CUSE enables character devices to be implemented from userland much * like FUSE allows filesystems. On initialization /dev/cuse is * created. By opening the file and replying to the CUSE_INIT request * userland CUSE server can create a character device. After that the * operation is very similar to FUSE. * * A CUSE instance involves the following objects. * * cuse_conn : contains fuse_conn and serves as bonding structure * channel : file handle connected to the userland CUSE server * cdev : the implemented character device * dev : generic device for cdev * * Note that 'channel' is what 'dev' is in FUSE. As CUSE deals with * devices, it's called 'channel' to reduce confusion. * * channel determines when the character device dies. When channel is * closed, everything begins to destruct. The cuse_conn is taken off * the lookup table preventing further access from cdev, cdev and * generic device are removed and the base reference of cuse_conn is * put. * * On each open, the matching cuse_conn is looked up and if found an * additional reference is taken which is released when the file is * closed. */ #define pr_fmt(fmt) … #include <linux/fuse.h> #include <linux/cdev.h> #include <linux/device.h> #include <linux/file.h> #include <linux/fs.h> #include <linux/kdev_t.h> #include <linux/kthread.h> #include <linux/list.h> #include <linux/magic.h> #include <linux/miscdevice.h> #include <linux/mutex.h> #include <linux/slab.h> #include <linux/stat.h> #include <linux/module.h> #include <linux/uio.h> #include <linux/user_namespace.h> #include "fuse_i.h" #define CUSE_CONNTBL_LEN … struct cuse_conn { … }; static DEFINE_MUTEX(cuse_lock); /* protects registration */ static struct list_head cuse_conntbl[CUSE_CONNTBL_LEN]; static struct class *cuse_class; static struct cuse_conn *fc_to_cc(struct fuse_conn *fc) { … } static struct list_head *cuse_conntbl_head(dev_t devt) { … } /************************************************************************** * CUSE frontend operations * * These are file operations for the character device. * * On open, CUSE opens a file from the FUSE mnt and stores it to * private_data of the open file. All other ops call FUSE ops on the * FUSE file. */ static ssize_t cuse_read_iter(struct kiocb *kiocb, struct iov_iter *to) { … } static ssize_t cuse_write_iter(struct kiocb *kiocb, struct iov_iter *from) { … } static int cuse_open(struct inode *inode, struct file *file) { … } static int cuse_release(struct inode *inode, struct file *file) { … } static long cuse_file_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { … } static long cuse_file_compat_ioctl(struct file *file, unsigned int cmd, unsigned long arg) { … } static const struct file_operations cuse_frontend_fops = …; /************************************************************************** * CUSE channel initialization and destruction */ struct cuse_devinfo { … }; /** * cuse_parse_one - parse one key=value pair * @pp: i/o parameter for the current position * @end: points to one past the end of the packed string * @keyp: out parameter for key * @valp: out parameter for value * * *@pp points to packed strings - "key0=val0\0key1=val1\0" which ends * at @end - 1. This function parses one pair and set *@keyp to the * start of the key and *@valp to the start of the value. Note that * the original string is modified such that the key string is * terminated with '\0'. *@pp is updated to point to the next string. * * RETURNS: * 1 on successful parse, 0 on EOF, -errno on failure. */ static int cuse_parse_one(char **pp, char *end, char **keyp, char **valp) { … } /** * cuse_parse_devinfo - parse device info * @p: device info string * @len: length of device info string * @devinfo: out parameter for parsed device info * * Parse @p to extract device info and store it into @devinfo. String * pointed to by @p is modified by parsing and @devinfo points into * them, so @p shouldn't be freed while @devinfo is in use. * * RETURNS: * 0 on success, -errno on failure. */ static int cuse_parse_devinfo(char *p, size_t len, struct cuse_devinfo *devinfo) { … } static void cuse_gendev_release(struct device *dev) { … } struct cuse_init_args { … }; /** * cuse_process_init_reply - finish initializing CUSE channel * * @fm: The fuse mount information containing the CUSE connection. * @args: The arguments passed to the init reply. * @error: The error code signifying if any error occurred during the process. * * This function creates the character device and sets up all the * required data structures for it. Please read the comment at the * top of this file for high level overview. */ static void cuse_process_init_reply(struct fuse_mount *fm, struct fuse_args *args, int error) { … } static int cuse_send_init(struct cuse_conn *cc) { … } static void cuse_fc_release(struct fuse_conn *fc) { … } /** * cuse_channel_open - open method for /dev/cuse * @inode: inode for /dev/cuse * @file: file struct being opened * * Userland CUSE server can create a CUSE device by opening /dev/cuse * and replying to the initialization request kernel sends. This * function is responsible for handling CUSE device initialization. * Because the fd opened by this function is used during * initialization, this function only creates cuse_conn and sends * init. The rest is delegated to a kthread. * * RETURNS: * 0 on success, -errno on failure. */ static int cuse_channel_open(struct inode *inode, struct file *file) { … } /** * cuse_channel_release - release method for /dev/cuse * @inode: inode for /dev/cuse * @file: file struct being closed * * Disconnect the channel, deregister CUSE device and initiate * destruction by putting the default reference. * * RETURNS: * 0 on success, -errno on failure. */ static int cuse_channel_release(struct inode *inode, struct file *file) { … } static struct file_operations cuse_channel_fops; /* initialized during init */ /************************************************************************** * Misc stuff and module initializatiion * * CUSE exports the same set of attributes to sysfs as fusectl. */ static ssize_t cuse_class_waiting_show(struct device *dev, struct device_attribute *attr, char *buf) { … } static DEVICE_ATTR(waiting, 0400, cuse_class_waiting_show, NULL); static ssize_t cuse_class_abort_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { … } static DEVICE_ATTR(abort, 0200, NULL, cuse_class_abort_store); static struct attribute *cuse_class_dev_attrs[] = …; ATTRIBUTE_GROUPS(…); static struct miscdevice cuse_miscdev = …; MODULE_ALIAS_MISCDEV(…); MODULE_ALIAS(…) …; static int __init cuse_init(void) { … } static void __exit cuse_exit(void) { … } module_init(…) …; module_exit(cuse_exit); MODULE_AUTHOR(…) …; MODULE_DESCRIPTION(…) …; MODULE_LICENSE(…) …;
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