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

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