xref: /openbmc/linux/drivers/base/devtmpfs.c (revision e23feb16)
1 /*
2  * devtmpfs - kernel-maintained tmpfs-based /dev
3  *
4  * Copyright (C) 2009, Kay Sievers <kay.sievers@vrfy.org>
5  *
6  * During bootup, before any driver core device is registered,
7  * devtmpfs, a tmpfs-based filesystem is created. Every driver-core
8  * device which requests a device node, will add a node in this
9  * filesystem.
10  * By default, all devices are named after the name of the device,
11  * owned by root and have a default mode of 0600. Subsystems can
12  * overwrite the default setting if needed.
13  */
14 
15 #include <linux/kernel.h>
16 #include <linux/syscalls.h>
17 #include <linux/mount.h>
18 #include <linux/device.h>
19 #include <linux/genhd.h>
20 #include <linux/namei.h>
21 #include <linux/fs.h>
22 #include <linux/shmem_fs.h>
23 #include <linux/ramfs.h>
24 #include <linux/sched.h>
25 #include <linux/slab.h>
26 #include <linux/kthread.h>
27 #include "base.h"
28 
29 static struct task_struct *thread;
30 
31 #if defined CONFIG_DEVTMPFS_MOUNT
32 static int mount_dev = 1;
33 #else
34 static int mount_dev;
35 #endif
36 
37 static DEFINE_SPINLOCK(req_lock);
38 
39 static struct req {
40 	struct req *next;
41 	struct completion done;
42 	int err;
43 	const char *name;
44 	umode_t mode;	/* 0 => delete */
45 	kuid_t uid;
46 	kgid_t gid;
47 	struct device *dev;
48 } *requests;
49 
50 static int __init mount_param(char *str)
51 {
52 	mount_dev = simple_strtoul(str, NULL, 0);
53 	return 1;
54 }
55 __setup("devtmpfs.mount=", mount_param);
56 
57 static struct dentry *dev_mount(struct file_system_type *fs_type, int flags,
58 		      const char *dev_name, void *data)
59 {
60 #ifdef CONFIG_TMPFS
61 	return mount_single(fs_type, flags, data, shmem_fill_super);
62 #else
63 	return mount_single(fs_type, flags, data, ramfs_fill_super);
64 #endif
65 }
66 
67 static struct file_system_type dev_fs_type = {
68 	.name = "devtmpfs",
69 	.mount = dev_mount,
70 	.kill_sb = kill_litter_super,
71 };
72 
73 #ifdef CONFIG_BLOCK
74 static inline int is_blockdev(struct device *dev)
75 {
76 	return dev->class == &block_class;
77 }
78 #else
79 static inline int is_blockdev(struct device *dev) { return 0; }
80 #endif
81 
82 int devtmpfs_create_node(struct device *dev)
83 {
84 	const char *tmp = NULL;
85 	struct req req;
86 
87 	if (!thread)
88 		return 0;
89 
90 	req.mode = 0;
91 	req.uid = GLOBAL_ROOT_UID;
92 	req.gid = GLOBAL_ROOT_GID;
93 	req.name = device_get_devnode(dev, &req.mode, &req.uid, &req.gid, &tmp);
94 	if (!req.name)
95 		return -ENOMEM;
96 
97 	if (req.mode == 0)
98 		req.mode = 0600;
99 	if (is_blockdev(dev))
100 		req.mode |= S_IFBLK;
101 	else
102 		req.mode |= S_IFCHR;
103 
104 	req.dev = dev;
105 
106 	init_completion(&req.done);
107 
108 	spin_lock(&req_lock);
109 	req.next = requests;
110 	requests = &req;
111 	spin_unlock(&req_lock);
112 
113 	wake_up_process(thread);
114 	wait_for_completion(&req.done);
115 
116 	kfree(tmp);
117 
118 	return req.err;
119 }
120 
121 int devtmpfs_delete_node(struct device *dev)
122 {
123 	const char *tmp = NULL;
124 	struct req req;
125 
126 	if (!thread)
127 		return 0;
128 
129 	req.name = device_get_devnode(dev, NULL, NULL, NULL, &tmp);
130 	if (!req.name)
131 		return -ENOMEM;
132 
133 	req.mode = 0;
134 	req.dev = dev;
135 
136 	init_completion(&req.done);
137 
138 	spin_lock(&req_lock);
139 	req.next = requests;
140 	requests = &req;
141 	spin_unlock(&req_lock);
142 
143 	wake_up_process(thread);
144 	wait_for_completion(&req.done);
145 
146 	kfree(tmp);
147 	return req.err;
148 }
149 
150 static int dev_mkdir(const char *name, umode_t mode)
151 {
152 	struct dentry *dentry;
153 	struct path path;
154 	int err;
155 
156 	dentry = kern_path_create(AT_FDCWD, name, &path, LOOKUP_DIRECTORY);
157 	if (IS_ERR(dentry))
158 		return PTR_ERR(dentry);
159 
160 	err = vfs_mkdir(path.dentry->d_inode, dentry, mode);
161 	if (!err)
162 		/* mark as kernel-created inode */
163 		dentry->d_inode->i_private = &thread;
164 	done_path_create(&path, dentry);
165 	return err;
166 }
167 
168 static int create_path(const char *nodepath)
169 {
170 	char *path;
171 	char *s;
172 	int err = 0;
173 
174 	/* parent directories do not exist, create them */
175 	path = kstrdup(nodepath, GFP_KERNEL);
176 	if (!path)
177 		return -ENOMEM;
178 
179 	s = path;
180 	for (;;) {
181 		s = strchr(s, '/');
182 		if (!s)
183 			break;
184 		s[0] = '\0';
185 		err = dev_mkdir(path, 0755);
186 		if (err && err != -EEXIST)
187 			break;
188 		s[0] = '/';
189 		s++;
190 	}
191 	kfree(path);
192 	return err;
193 }
194 
195 static int handle_create(const char *nodename, umode_t mode, kuid_t uid,
196 			 kgid_t gid, struct device *dev)
197 {
198 	struct dentry *dentry;
199 	struct path path;
200 	int err;
201 
202 	dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
203 	if (dentry == ERR_PTR(-ENOENT)) {
204 		create_path(nodename);
205 		dentry = kern_path_create(AT_FDCWD, nodename, &path, 0);
206 	}
207 	if (IS_ERR(dentry))
208 		return PTR_ERR(dentry);
209 
210 	err = vfs_mknod(path.dentry->d_inode, dentry, mode, dev->devt);
211 	if (!err) {
212 		struct iattr newattrs;
213 
214 		newattrs.ia_mode = mode;
215 		newattrs.ia_uid = uid;
216 		newattrs.ia_gid = gid;
217 		newattrs.ia_valid = ATTR_MODE|ATTR_UID|ATTR_GID;
218 		mutex_lock(&dentry->d_inode->i_mutex);
219 		notify_change(dentry, &newattrs);
220 		mutex_unlock(&dentry->d_inode->i_mutex);
221 
222 		/* mark as kernel-created inode */
223 		dentry->d_inode->i_private = &thread;
224 	}
225 	done_path_create(&path, dentry);
226 	return err;
227 }
228 
229 static int dev_rmdir(const char *name)
230 {
231 	struct path parent;
232 	struct dentry *dentry;
233 	int err;
234 
235 	dentry = kern_path_locked(name, &parent);
236 	if (IS_ERR(dentry))
237 		return PTR_ERR(dentry);
238 	if (dentry->d_inode) {
239 		if (dentry->d_inode->i_private == &thread)
240 			err = vfs_rmdir(parent.dentry->d_inode, dentry);
241 		else
242 			err = -EPERM;
243 	} else {
244 		err = -ENOENT;
245 	}
246 	dput(dentry);
247 	mutex_unlock(&parent.dentry->d_inode->i_mutex);
248 	path_put(&parent);
249 	return err;
250 }
251 
252 static int delete_path(const char *nodepath)
253 {
254 	const char *path;
255 	int err = 0;
256 
257 	path = kstrdup(nodepath, GFP_KERNEL);
258 	if (!path)
259 		return -ENOMEM;
260 
261 	for (;;) {
262 		char *base;
263 
264 		base = strrchr(path, '/');
265 		if (!base)
266 			break;
267 		base[0] = '\0';
268 		err = dev_rmdir(path);
269 		if (err)
270 			break;
271 	}
272 
273 	kfree(path);
274 	return err;
275 }
276 
277 static int dev_mynode(struct device *dev, struct inode *inode, struct kstat *stat)
278 {
279 	/* did we create it */
280 	if (inode->i_private != &thread)
281 		return 0;
282 
283 	/* does the dev_t match */
284 	if (is_blockdev(dev)) {
285 		if (!S_ISBLK(stat->mode))
286 			return 0;
287 	} else {
288 		if (!S_ISCHR(stat->mode))
289 			return 0;
290 	}
291 	if (stat->rdev != dev->devt)
292 		return 0;
293 
294 	/* ours */
295 	return 1;
296 }
297 
298 static int handle_remove(const char *nodename, struct device *dev)
299 {
300 	struct path parent;
301 	struct dentry *dentry;
302 	int deleted = 1;
303 	int err;
304 
305 	dentry = kern_path_locked(nodename, &parent);
306 	if (IS_ERR(dentry))
307 		return PTR_ERR(dentry);
308 
309 	if (dentry->d_inode) {
310 		struct kstat stat;
311 		struct path p = {.mnt = parent.mnt, .dentry = dentry};
312 		err = vfs_getattr(&p, &stat);
313 		if (!err && dev_mynode(dev, dentry->d_inode, &stat)) {
314 			struct iattr newattrs;
315 			/*
316 			 * before unlinking this node, reset permissions
317 			 * of possible references like hardlinks
318 			 */
319 			newattrs.ia_uid = GLOBAL_ROOT_UID;
320 			newattrs.ia_gid = GLOBAL_ROOT_GID;
321 			newattrs.ia_mode = stat.mode & ~0777;
322 			newattrs.ia_valid =
323 				ATTR_UID|ATTR_GID|ATTR_MODE;
324 			mutex_lock(&dentry->d_inode->i_mutex);
325 			notify_change(dentry, &newattrs);
326 			mutex_unlock(&dentry->d_inode->i_mutex);
327 			err = vfs_unlink(parent.dentry->d_inode, dentry);
328 			if (!err || err == -ENOENT)
329 				deleted = 1;
330 		}
331 	} else {
332 		err = -ENOENT;
333 	}
334 	dput(dentry);
335 	mutex_unlock(&parent.dentry->d_inode->i_mutex);
336 
337 	path_put(&parent);
338 	if (deleted && strchr(nodename, '/'))
339 		delete_path(nodename);
340 	return err;
341 }
342 
343 /*
344  * If configured, or requested by the commandline, devtmpfs will be
345  * auto-mounted after the kernel mounted the root filesystem.
346  */
347 int devtmpfs_mount(const char *mntdir)
348 {
349 	int err;
350 
351 	if (!mount_dev)
352 		return 0;
353 
354 	if (!thread)
355 		return 0;
356 
357 	err = sys_mount("devtmpfs", (char *)mntdir, "devtmpfs", MS_SILENT, NULL);
358 	if (err)
359 		printk(KERN_INFO "devtmpfs: error mounting %i\n", err);
360 	else
361 		printk(KERN_INFO "devtmpfs: mounted\n");
362 	return err;
363 }
364 
365 static DECLARE_COMPLETION(setup_done);
366 
367 static int handle(const char *name, umode_t mode, kuid_t uid, kgid_t gid,
368 		  struct device *dev)
369 {
370 	if (mode)
371 		return handle_create(name, mode, uid, gid, dev);
372 	else
373 		return handle_remove(name, dev);
374 }
375 
376 static int devtmpfsd(void *p)
377 {
378 	char options[] = "mode=0755";
379 	int *err = p;
380 	*err = sys_unshare(CLONE_NEWNS);
381 	if (*err)
382 		goto out;
383 	*err = sys_mount("devtmpfs", "/", "devtmpfs", MS_SILENT, options);
384 	if (*err)
385 		goto out;
386 	sys_chdir("/.."); /* will traverse into overmounted root */
387 	sys_chroot(".");
388 	complete(&setup_done);
389 	while (1) {
390 		spin_lock(&req_lock);
391 		while (requests) {
392 			struct req *req = requests;
393 			requests = NULL;
394 			spin_unlock(&req_lock);
395 			while (req) {
396 				struct req *next = req->next;
397 				req->err = handle(req->name, req->mode,
398 						  req->uid, req->gid, req->dev);
399 				complete(&req->done);
400 				req = next;
401 			}
402 			spin_lock(&req_lock);
403 		}
404 		__set_current_state(TASK_INTERRUPTIBLE);
405 		spin_unlock(&req_lock);
406 		schedule();
407 	}
408 	return 0;
409 out:
410 	complete(&setup_done);
411 	return *err;
412 }
413 
414 /*
415  * Create devtmpfs instance, driver-core devices will add their device
416  * nodes here.
417  */
418 int __init devtmpfs_init(void)
419 {
420 	int err = register_filesystem(&dev_fs_type);
421 	if (err) {
422 		printk(KERN_ERR "devtmpfs: unable to register devtmpfs "
423 		       "type %i\n", err);
424 		return err;
425 	}
426 
427 	thread = kthread_run(devtmpfsd, &err, "kdevtmpfs");
428 	if (!IS_ERR(thread)) {
429 		wait_for_completion(&setup_done);
430 	} else {
431 		err = PTR_ERR(thread);
432 		thread = NULL;
433 	}
434 
435 	if (err) {
436 		printk(KERN_ERR "devtmpfs: unable to create devtmpfs %i\n", err);
437 		unregister_filesystem(&dev_fs_type);
438 		return err;
439 	}
440 
441 	printk(KERN_INFO "devtmpfs: initialized\n");
442 	return 0;
443 }
444