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Linux/drivers/base/devtmpfs.c

  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, NULL);
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 = 0;
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, NULL);
326                         mutex_unlock(&dentry->d_inode->i_mutex);
327                         err = vfs_unlink(parent.dentry->d_inode, dentry, NULL);
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 

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