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TOMOYO Linux Cross Reference
Linux/fs/tracefs/inode.c

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  1 /*
  2  *  inode.c - part of tracefs, a pseudo file system for activating tracing
  3  *
  4  * Based on debugfs by: Greg Kroah-Hartman <greg@kroah.com>
  5  *
  6  *  Copyright (C) 2014 Red Hat Inc, author: Steven Rostedt <srostedt@redhat.com>
  7  *
  8  *      This program is free software; you can redistribute it and/or
  9  *      modify it under the terms of the GNU General Public License version
 10  *      2 as published by the Free Software Foundation.
 11  *
 12  * tracefs is the file system that is used by the tracing infrastructure.
 13  *
 14  */
 15 
 16 #include <linux/module.h>
 17 #include <linux/fs.h>
 18 #include <linux/mount.h>
 19 #include <linux/kobject.h>
 20 #include <linux/namei.h>
 21 #include <linux/tracefs.h>
 22 #include <linux/fsnotify.h>
 23 #include <linux/seq_file.h>
 24 #include <linux/parser.h>
 25 #include <linux/magic.h>
 26 #include <linux/slab.h>
 27 
 28 #define TRACEFS_DEFAULT_MODE    0700
 29 
 30 static struct vfsmount *tracefs_mount;
 31 static int tracefs_mount_count;
 32 static bool tracefs_registered;
 33 
 34 static ssize_t default_read_file(struct file *file, char __user *buf,
 35                                  size_t count, loff_t *ppos)
 36 {
 37         return 0;
 38 }
 39 
 40 static ssize_t default_write_file(struct file *file, const char __user *buf,
 41                                    size_t count, loff_t *ppos)
 42 {
 43         return count;
 44 }
 45 
 46 static const struct file_operations tracefs_file_operations = {
 47         .read =         default_read_file,
 48         .write =        default_write_file,
 49         .open =         simple_open,
 50         .llseek =       noop_llseek,
 51 };
 52 
 53 static struct tracefs_dir_ops {
 54         int (*mkdir)(const char *name);
 55         int (*rmdir)(const char *name);
 56 } tracefs_ops;
 57 
 58 static char *get_dname(struct dentry *dentry)
 59 {
 60         const char *dname;
 61         char *name;
 62         int len = dentry->d_name.len;
 63 
 64         dname = dentry->d_name.name;
 65         name = kmalloc(len + 1, GFP_KERNEL);
 66         if (!name)
 67                 return NULL;
 68         memcpy(name, dname, len);
 69         name[len] = 0;
 70         return name;
 71 }
 72 
 73 static int tracefs_syscall_mkdir(struct inode *inode, struct dentry *dentry, umode_t mode)
 74 {
 75         char *name;
 76         int ret;
 77 
 78         name = get_dname(dentry);
 79         if (!name)
 80                 return -ENOMEM;
 81 
 82         /*
 83          * The mkdir call can call the generic functions that create
 84          * the files within the tracefs system. It is up to the individual
 85          * mkdir routine to handle races.
 86          */
 87         inode_unlock(inode);
 88         ret = tracefs_ops.mkdir(name);
 89         inode_lock(inode);
 90 
 91         kfree(name);
 92 
 93         return ret;
 94 }
 95 
 96 static int tracefs_syscall_rmdir(struct inode *inode, struct dentry *dentry)
 97 {
 98         char *name;
 99         int ret;
100 
101         name = get_dname(dentry);
102         if (!name)
103                 return -ENOMEM;
104 
105         /*
106          * The rmdir call can call the generic functions that create
107          * the files within the tracefs system. It is up to the individual
108          * rmdir routine to handle races.
109          * This time we need to unlock not only the parent (inode) but
110          * also the directory that is being deleted.
111          */
112         inode_unlock(inode);
113         inode_unlock(dentry->d_inode);
114 
115         ret = tracefs_ops.rmdir(name);
116 
117         inode_lock_nested(inode, I_MUTEX_PARENT);
118         inode_lock(dentry->d_inode);
119 
120         kfree(name);
121 
122         return ret;
123 }
124 
125 static const struct inode_operations tracefs_dir_inode_operations = {
126         .lookup         = simple_lookup,
127         .mkdir          = tracefs_syscall_mkdir,
128         .rmdir          = tracefs_syscall_rmdir,
129 };
130 
131 static struct inode *tracefs_get_inode(struct super_block *sb)
132 {
133         struct inode *inode = new_inode(sb);
134         if (inode) {
135                 inode->i_ino = get_next_ino();
136                 inode->i_atime = inode->i_mtime = inode->i_ctime = current_time(inode);
137         }
138         return inode;
139 }
140 
141 struct tracefs_mount_opts {
142         kuid_t uid;
143         kgid_t gid;
144         umode_t mode;
145 };
146 
147 enum {
148         Opt_uid,
149         Opt_gid,
150         Opt_mode,
151         Opt_err
152 };
153 
154 static const match_table_t tokens = {
155         {Opt_uid, "uid=%u"},
156         {Opt_gid, "gid=%u"},
157         {Opt_mode, "mode=%o"},
158         {Opt_err, NULL}
159 };
160 
161 struct tracefs_fs_info {
162         struct tracefs_mount_opts mount_opts;
163 };
164 
165 static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
166 {
167         substring_t args[MAX_OPT_ARGS];
168         int option;
169         int token;
170         kuid_t uid;
171         kgid_t gid;
172         char *p;
173 
174         opts->mode = TRACEFS_DEFAULT_MODE;
175 
176         while ((p = strsep(&data, ",")) != NULL) {
177                 if (!*p)
178                         continue;
179 
180                 token = match_token(p, tokens, args);
181                 switch (token) {
182                 case Opt_uid:
183                         if (match_int(&args[0], &option))
184                                 return -EINVAL;
185                         uid = make_kuid(current_user_ns(), option);
186                         if (!uid_valid(uid))
187                                 return -EINVAL;
188                         opts->uid = uid;
189                         break;
190                 case Opt_gid:
191                         if (match_int(&args[0], &option))
192                                 return -EINVAL;
193                         gid = make_kgid(current_user_ns(), option);
194                         if (!gid_valid(gid))
195                                 return -EINVAL;
196                         opts->gid = gid;
197                         break;
198                 case Opt_mode:
199                         if (match_octal(&args[0], &option))
200                                 return -EINVAL;
201                         opts->mode = option & S_IALLUGO;
202                         break;
203                 /*
204                  * We might like to report bad mount options here;
205                  * but traditionally tracefs has ignored all mount options
206                  */
207                 }
208         }
209 
210         return 0;
211 }
212 
213 static int tracefs_apply_options(struct super_block *sb)
214 {
215         struct tracefs_fs_info *fsi = sb->s_fs_info;
216         struct inode *inode = sb->s_root->d_inode;
217         struct tracefs_mount_opts *opts = &fsi->mount_opts;
218 
219         inode->i_mode &= ~S_IALLUGO;
220         inode->i_mode |= opts->mode;
221 
222         inode->i_uid = opts->uid;
223         inode->i_gid = opts->gid;
224 
225         return 0;
226 }
227 
228 static int tracefs_remount(struct super_block *sb, int *flags, char *data)
229 {
230         int err;
231         struct tracefs_fs_info *fsi = sb->s_fs_info;
232 
233         sync_filesystem(sb);
234         err = tracefs_parse_options(data, &fsi->mount_opts);
235         if (err)
236                 goto fail;
237 
238         tracefs_apply_options(sb);
239 
240 fail:
241         return err;
242 }
243 
244 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
245 {
246         struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
247         struct tracefs_mount_opts *opts = &fsi->mount_opts;
248 
249         if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
250                 seq_printf(m, ",uid=%u",
251                            from_kuid_munged(&init_user_ns, opts->uid));
252         if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
253                 seq_printf(m, ",gid=%u",
254                            from_kgid_munged(&init_user_ns, opts->gid));
255         if (opts->mode != TRACEFS_DEFAULT_MODE)
256                 seq_printf(m, ",mode=%o", opts->mode);
257 
258         return 0;
259 }
260 
261 static const struct super_operations tracefs_super_operations = {
262         .statfs         = simple_statfs,
263         .remount_fs     = tracefs_remount,
264         .show_options   = tracefs_show_options,
265 };
266 
267 static int trace_fill_super(struct super_block *sb, void *data, int silent)
268 {
269         static const struct tree_descr trace_files[] = {{""}};
270         struct tracefs_fs_info *fsi;
271         int err;
272 
273         fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
274         sb->s_fs_info = fsi;
275         if (!fsi) {
276                 err = -ENOMEM;
277                 goto fail;
278         }
279 
280         err = tracefs_parse_options(data, &fsi->mount_opts);
281         if (err)
282                 goto fail;
283 
284         err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
285         if (err)
286                 goto fail;
287 
288         sb->s_op = &tracefs_super_operations;
289 
290         tracefs_apply_options(sb);
291 
292         return 0;
293 
294 fail:
295         kfree(fsi);
296         sb->s_fs_info = NULL;
297         return err;
298 }
299 
300 static struct dentry *trace_mount(struct file_system_type *fs_type,
301                         int flags, const char *dev_name,
302                         void *data)
303 {
304         return mount_single(fs_type, flags, data, trace_fill_super);
305 }
306 
307 static struct file_system_type trace_fs_type = {
308         .owner =        THIS_MODULE,
309         .name =         "tracefs",
310         .mount =        trace_mount,
311         .kill_sb =      kill_litter_super,
312 };
313 MODULE_ALIAS_FS("tracefs");
314 
315 static struct dentry *start_creating(const char *name, struct dentry *parent)
316 {
317         struct dentry *dentry;
318         int error;
319 
320         pr_debug("tracefs: creating file '%s'\n",name);
321 
322         error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
323                               &tracefs_mount_count);
324         if (error)
325                 return ERR_PTR(error);
326 
327         /* If the parent is not specified, we create it in the root.
328          * We need the root dentry to do this, which is in the super
329          * block. A pointer to that is in the struct vfsmount that we
330          * have around.
331          */
332         if (!parent)
333                 parent = tracefs_mount->mnt_root;
334 
335         inode_lock(parent->d_inode);
336         dentry = lookup_one_len(name, parent, strlen(name));
337         if (!IS_ERR(dentry) && dentry->d_inode) {
338                 dput(dentry);
339                 dentry = ERR_PTR(-EEXIST);
340         }
341 
342         if (IS_ERR(dentry)) {
343                 inode_unlock(parent->d_inode);
344                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
345         }
346 
347         return dentry;
348 }
349 
350 static struct dentry *failed_creating(struct dentry *dentry)
351 {
352         inode_unlock(dentry->d_parent->d_inode);
353         dput(dentry);
354         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
355         return NULL;
356 }
357 
358 static struct dentry *end_creating(struct dentry *dentry)
359 {
360         inode_unlock(dentry->d_parent->d_inode);
361         return dentry;
362 }
363 
364 /**
365  * tracefs_create_file - create a file in the tracefs filesystem
366  * @name: a pointer to a string containing the name of the file to create.
367  * @mode: the permission that the file should have.
368  * @parent: a pointer to the parent dentry for this file.  This should be a
369  *          directory dentry if set.  If this parameter is NULL, then the
370  *          file will be created in the root of the tracefs filesystem.
371  * @data: a pointer to something that the caller will want to get to later
372  *        on.  The inode.i_private pointer will point to this value on
373  *        the open() call.
374  * @fops: a pointer to a struct file_operations that should be used for
375  *        this file.
376  *
377  * This is the basic "create a file" function for tracefs.  It allows for a
378  * wide range of flexibility in creating a file, or a directory (if you want
379  * to create a directory, the tracefs_create_dir() function is
380  * recommended to be used instead.)
381  *
382  * This function will return a pointer to a dentry if it succeeds.  This
383  * pointer must be passed to the tracefs_remove() function when the file is
384  * to be removed (no automatic cleanup happens if your module is unloaded,
385  * you are responsible here.)  If an error occurs, %NULL will be returned.
386  *
387  * If tracefs is not enabled in the kernel, the value -%ENODEV will be
388  * returned.
389  */
390 struct dentry *tracefs_create_file(const char *name, umode_t mode,
391                                    struct dentry *parent, void *data,
392                                    const struct file_operations *fops)
393 {
394         struct dentry *dentry;
395         struct inode *inode;
396 
397         if (!(mode & S_IFMT))
398                 mode |= S_IFREG;
399         BUG_ON(!S_ISREG(mode));
400         dentry = start_creating(name, parent);
401 
402         if (IS_ERR(dentry))
403                 return NULL;
404 
405         inode = tracefs_get_inode(dentry->d_sb);
406         if (unlikely(!inode))
407                 return failed_creating(dentry);
408 
409         inode->i_mode = mode;
410         inode->i_fop = fops ? fops : &tracefs_file_operations;
411         inode->i_private = data;
412         d_instantiate(dentry, inode);
413         fsnotify_create(dentry->d_parent->d_inode, dentry);
414         return end_creating(dentry);
415 }
416 
417 static struct dentry *__create_dir(const char *name, struct dentry *parent,
418                                    const struct inode_operations *ops)
419 {
420         struct dentry *dentry = start_creating(name, parent);
421         struct inode *inode;
422 
423         if (IS_ERR(dentry))
424                 return NULL;
425 
426         inode = tracefs_get_inode(dentry->d_sb);
427         if (unlikely(!inode))
428                 return failed_creating(dentry);
429 
430         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
431         inode->i_op = ops;
432         inode->i_fop = &simple_dir_operations;
433 
434         /* directory inodes start off with i_nlink == 2 (for "." entry) */
435         inc_nlink(inode);
436         d_instantiate(dentry, inode);
437         inc_nlink(dentry->d_parent->d_inode);
438         fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
439         return end_creating(dentry);
440 }
441 
442 /**
443  * tracefs_create_dir - create a directory in the tracefs filesystem
444  * @name: a pointer to a string containing the name of the directory to
445  *        create.
446  * @parent: a pointer to the parent dentry for this file.  This should be a
447  *          directory dentry if set.  If this parameter is NULL, then the
448  *          directory will be created in the root of the tracefs filesystem.
449  *
450  * This function creates a directory in tracefs with the given name.
451  *
452  * This function will return a pointer to a dentry if it succeeds.  This
453  * pointer must be passed to the tracefs_remove() function when the file is
454  * to be removed. If an error occurs, %NULL will be returned.
455  *
456  * If tracing is not enabled in the kernel, the value -%ENODEV will be
457  * returned.
458  */
459 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
460 {
461         return __create_dir(name, parent, &simple_dir_inode_operations);
462 }
463 
464 /**
465  * tracefs_create_instance_dir - create the tracing instances directory
466  * @name: The name of the instances directory to create
467  * @parent: The parent directory that the instances directory will exist
468  * @mkdir: The function to call when a mkdir is performed.
469  * @rmdir: The function to call when a rmdir is performed.
470  *
471  * Only one instances directory is allowed.
472  *
473  * The instances directory is special as it allows for mkdir and rmdir to
474  * to be done by userspace. When a mkdir or rmdir is performed, the inode
475  * locks are released and the methhods passed in (@mkdir and @rmdir) are
476  * called without locks and with the name of the directory being created
477  * within the instances directory.
478  *
479  * Returns the dentry of the instances directory.
480  */
481 struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
482                                           int (*mkdir)(const char *name),
483                                           int (*rmdir)(const char *name))
484 {
485         struct dentry *dentry;
486 
487         /* Only allow one instance of the instances directory. */
488         if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
489                 return NULL;
490 
491         dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
492         if (!dentry)
493                 return NULL;
494 
495         tracefs_ops.mkdir = mkdir;
496         tracefs_ops.rmdir = rmdir;
497 
498         return dentry;
499 }
500 
501 static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
502 {
503         int ret = 0;
504 
505         if (simple_positive(dentry)) {
506                 if (dentry->d_inode) {
507                         dget(dentry);
508                         switch (dentry->d_inode->i_mode & S_IFMT) {
509                         case S_IFDIR:
510                                 ret = simple_rmdir(parent->d_inode, dentry);
511                                 break;
512                         default:
513                                 simple_unlink(parent->d_inode, dentry);
514                                 break;
515                         }
516                         if (!ret)
517                                 d_delete(dentry);
518                         dput(dentry);
519                 }
520         }
521         return ret;
522 }
523 
524 /**
525  * tracefs_remove - removes a file or directory from the tracefs filesystem
526  * @dentry: a pointer to a the dentry of the file or directory to be
527  *          removed.
528  *
529  * This function removes a file or directory in tracefs that was previously
530  * created with a call to another tracefs function (like
531  * tracefs_create_file() or variants thereof.)
532  */
533 void tracefs_remove(struct dentry *dentry)
534 {
535         struct dentry *parent;
536         int ret;
537 
538         if (IS_ERR_OR_NULL(dentry))
539                 return;
540 
541         parent = dentry->d_parent;
542         inode_lock(parent->d_inode);
543         ret = __tracefs_remove(dentry, parent);
544         inode_unlock(parent->d_inode);
545         if (!ret)
546                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
547 }
548 
549 /**
550  * tracefs_remove_recursive - recursively removes a directory
551  * @dentry: a pointer to a the dentry of the directory to be removed.
552  *
553  * This function recursively removes a directory tree in tracefs that
554  * was previously created with a call to another tracefs function
555  * (like tracefs_create_file() or variants thereof.)
556  */
557 void tracefs_remove_recursive(struct dentry *dentry)
558 {
559         struct dentry *child, *parent;
560 
561         if (IS_ERR_OR_NULL(dentry))
562                 return;
563 
564         parent = dentry;
565  down:
566         inode_lock(parent->d_inode);
567  loop:
568         /*
569          * The parent->d_subdirs is protected by the d_lock. Outside that
570          * lock, the child can be unlinked and set to be freed which can
571          * use the d_u.d_child as the rcu head and corrupt this list.
572          */
573         spin_lock(&parent->d_lock);
574         list_for_each_entry(child, &parent->d_subdirs, d_child) {
575                 if (!simple_positive(child))
576                         continue;
577 
578                 /* perhaps simple_empty(child) makes more sense */
579                 if (!list_empty(&child->d_subdirs)) {
580                         spin_unlock(&parent->d_lock);
581                         inode_unlock(parent->d_inode);
582                         parent = child;
583                         goto down;
584                 }
585 
586                 spin_unlock(&parent->d_lock);
587 
588                 if (!__tracefs_remove(child, parent))
589                         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
590 
591                 /*
592                  * The parent->d_lock protects agaist child from unlinking
593                  * from d_subdirs. When releasing the parent->d_lock we can
594                  * no longer trust that the next pointer is valid.
595                  * Restart the loop. We'll skip this one with the
596                  * simple_positive() check.
597                  */
598                 goto loop;
599         }
600         spin_unlock(&parent->d_lock);
601 
602         inode_unlock(parent->d_inode);
603         child = parent;
604         parent = parent->d_parent;
605         inode_lock(parent->d_inode);
606 
607         if (child != dentry)
608                 /* go up */
609                 goto loop;
610 
611         if (!__tracefs_remove(child, parent))
612                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
613         inode_unlock(parent->d_inode);
614 }
615 
616 /**
617  * tracefs_initialized - Tells whether tracefs has been registered
618  */
619 bool tracefs_initialized(void)
620 {
621         return tracefs_registered;
622 }
623 
624 static int __init tracefs_init(void)
625 {
626         int retval;
627 
628         retval = sysfs_create_mount_point(kernel_kobj, "tracing");
629         if (retval)
630                 return -EINVAL;
631 
632         retval = register_filesystem(&trace_fs_type);
633         if (!retval)
634                 tracefs_registered = true;
635 
636         return retval;
637 }
638 core_initcall(tracefs_init);
639 

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