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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;
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 struct tree_descr trace_files[] = {{""}};
270         struct tracefs_fs_info *fsi;
271         int err;
272 
273         save_mount_options(sb, data);
274 
275         fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
276         sb->s_fs_info = fsi;
277         if (!fsi) {
278                 err = -ENOMEM;
279                 goto fail;
280         }
281 
282         err = tracefs_parse_options(data, &fsi->mount_opts);
283         if (err)
284                 goto fail;
285 
286         err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
287         if (err)
288                 goto fail;
289 
290         sb->s_op = &tracefs_super_operations;
291 
292         tracefs_apply_options(sb);
293 
294         return 0;
295 
296 fail:
297         kfree(fsi);
298         sb->s_fs_info = NULL;
299         return err;
300 }
301 
302 static struct dentry *trace_mount(struct file_system_type *fs_type,
303                         int flags, const char *dev_name,
304                         void *data)
305 {
306         return mount_single(fs_type, flags, data, trace_fill_super);
307 }
308 
309 static struct file_system_type trace_fs_type = {
310         .owner =        THIS_MODULE,
311         .name =         "tracefs",
312         .mount =        trace_mount,
313         .kill_sb =      kill_litter_super,
314 };
315 MODULE_ALIAS_FS("tracefs");
316 
317 static struct dentry *start_creating(const char *name, struct dentry *parent)
318 {
319         struct dentry *dentry;
320         int error;
321 
322         pr_debug("tracefs: creating file '%s'\n",name);
323 
324         error = simple_pin_fs(&trace_fs_type, &tracefs_mount,
325                               &tracefs_mount_count);
326         if (error)
327                 return ERR_PTR(error);
328 
329         /* If the parent is not specified, we create it in the root.
330          * We need the root dentry to do this, which is in the super
331          * block. A pointer to that is in the struct vfsmount that we
332          * have around.
333          */
334         if (!parent)
335                 parent = tracefs_mount->mnt_root;
336 
337         inode_lock(parent->d_inode);
338         dentry = lookup_one_len(name, parent, strlen(name));
339         if (!IS_ERR(dentry) && dentry->d_inode) {
340                 dput(dentry);
341                 dentry = ERR_PTR(-EEXIST);
342         }
343 
344         if (IS_ERR(dentry)) {
345                 inode_unlock(parent->d_inode);
346                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
347         }
348 
349         return dentry;
350 }
351 
352 static struct dentry *failed_creating(struct dentry *dentry)
353 {
354         inode_unlock(dentry->d_parent->d_inode);
355         dput(dentry);
356         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
357         return NULL;
358 }
359 
360 static struct dentry *end_creating(struct dentry *dentry)
361 {
362         inode_unlock(dentry->d_parent->d_inode);
363         return dentry;
364 }
365 
366 /**
367  * tracefs_create_file - create a file in the tracefs filesystem
368  * @name: a pointer to a string containing the name of the file to create.
369  * @mode: the permission that the file should have.
370  * @parent: a pointer to the parent dentry for this file.  This should be a
371  *          directory dentry if set.  If this parameter is NULL, then the
372  *          file will be created in the root of the tracefs filesystem.
373  * @data: a pointer to something that the caller will want to get to later
374  *        on.  The inode.i_private pointer will point to this value on
375  *        the open() call.
376  * @fops: a pointer to a struct file_operations that should be used for
377  *        this file.
378  *
379  * This is the basic "create a file" function for tracefs.  It allows for a
380  * wide range of flexibility in creating a file, or a directory (if you want
381  * to create a directory, the tracefs_create_dir() function is
382  * recommended to be used instead.)
383  *
384  * This function will return a pointer to a dentry if it succeeds.  This
385  * pointer must be passed to the tracefs_remove() function when the file is
386  * to be removed (no automatic cleanup happens if your module is unloaded,
387  * you are responsible here.)  If an error occurs, %NULL will be returned.
388  *
389  * If tracefs is not enabled in the kernel, the value -%ENODEV will be
390  * returned.
391  */
392 struct dentry *tracefs_create_file(const char *name, umode_t mode,
393                                    struct dentry *parent, void *data,
394                                    const struct file_operations *fops)
395 {
396         struct dentry *dentry;
397         struct inode *inode;
398 
399         if (!(mode & S_IFMT))
400                 mode |= S_IFREG;
401         BUG_ON(!S_ISREG(mode));
402         dentry = start_creating(name, parent);
403 
404         if (IS_ERR(dentry))
405                 return NULL;
406 
407         inode = tracefs_get_inode(dentry->d_sb);
408         if (unlikely(!inode))
409                 return failed_creating(dentry);
410 
411         inode->i_mode = mode;
412         inode->i_fop = fops ? fops : &tracefs_file_operations;
413         inode->i_private = data;
414         d_instantiate(dentry, inode);
415         fsnotify_create(dentry->d_parent->d_inode, dentry);
416         return end_creating(dentry);
417 }
418 
419 static struct dentry *__create_dir(const char *name, struct dentry *parent,
420                                    const struct inode_operations *ops)
421 {
422         struct dentry *dentry = start_creating(name, parent);
423         struct inode *inode;
424 
425         if (IS_ERR(dentry))
426                 return NULL;
427 
428         inode = tracefs_get_inode(dentry->d_sb);
429         if (unlikely(!inode))
430                 return failed_creating(dentry);
431 
432         inode->i_mode = S_IFDIR | S_IRWXU | S_IRUGO | S_IXUGO;
433         inode->i_op = ops;
434         inode->i_fop = &simple_dir_operations;
435 
436         /* directory inodes start off with i_nlink == 2 (for "." entry) */
437         inc_nlink(inode);
438         d_instantiate(dentry, inode);
439         inc_nlink(dentry->d_parent->d_inode);
440         fsnotify_mkdir(dentry->d_parent->d_inode, dentry);
441         return end_creating(dentry);
442 }
443 
444 /**
445  * tracefs_create_dir - create a directory in the tracefs filesystem
446  * @name: a pointer to a string containing the name of the directory to
447  *        create.
448  * @parent: a pointer to the parent dentry for this file.  This should be a
449  *          directory dentry if set.  If this parameter is NULL, then the
450  *          directory will be created in the root of the tracefs filesystem.
451  *
452  * This function creates a directory in tracefs with the given name.
453  *
454  * This function will return a pointer to a dentry if it succeeds.  This
455  * pointer must be passed to the tracefs_remove() function when the file is
456  * to be removed. If an error occurs, %NULL will be returned.
457  *
458  * If tracing is not enabled in the kernel, the value -%ENODEV will be
459  * returned.
460  */
461 struct dentry *tracefs_create_dir(const char *name, struct dentry *parent)
462 {
463         return __create_dir(name, parent, &simple_dir_inode_operations);
464 }
465 
466 /**
467  * tracefs_create_instance_dir - create the tracing instances directory
468  * @name: The name of the instances directory to create
469  * @parent: The parent directory that the instances directory will exist
470  * @mkdir: The function to call when a mkdir is performed.
471  * @rmdir: The function to call when a rmdir is performed.
472  *
473  * Only one instances directory is allowed.
474  *
475  * The instances directory is special as it allows for mkdir and rmdir to
476  * to be done by userspace. When a mkdir or rmdir is performed, the inode
477  * locks are released and the methhods passed in (@mkdir and @rmdir) are
478  * called without locks and with the name of the directory being created
479  * within the instances directory.
480  *
481  * Returns the dentry of the instances directory.
482  */
483 struct dentry *tracefs_create_instance_dir(const char *name, struct dentry *parent,
484                                           int (*mkdir)(const char *name),
485                                           int (*rmdir)(const char *name))
486 {
487         struct dentry *dentry;
488 
489         /* Only allow one instance of the instances directory. */
490         if (WARN_ON(tracefs_ops.mkdir || tracefs_ops.rmdir))
491                 return NULL;
492 
493         dentry = __create_dir(name, parent, &tracefs_dir_inode_operations);
494         if (!dentry)
495                 return NULL;
496 
497         tracefs_ops.mkdir = mkdir;
498         tracefs_ops.rmdir = rmdir;
499 
500         return dentry;
501 }
502 
503 static int __tracefs_remove(struct dentry *dentry, struct dentry *parent)
504 {
505         int ret = 0;
506 
507         if (simple_positive(dentry)) {
508                 if (dentry->d_inode) {
509                         dget(dentry);
510                         switch (dentry->d_inode->i_mode & S_IFMT) {
511                         case S_IFDIR:
512                                 ret = simple_rmdir(parent->d_inode, dentry);
513                                 break;
514                         default:
515                                 simple_unlink(parent->d_inode, dentry);
516                                 break;
517                         }
518                         if (!ret)
519                                 d_delete(dentry);
520                         dput(dentry);
521                 }
522         }
523         return ret;
524 }
525 
526 /**
527  * tracefs_remove - removes a file or directory from the tracefs filesystem
528  * @dentry: a pointer to a the dentry of the file or directory to be
529  *          removed.
530  *
531  * This function removes a file or directory in tracefs that was previously
532  * created with a call to another tracefs function (like
533  * tracefs_create_file() or variants thereof.)
534  */
535 void tracefs_remove(struct dentry *dentry)
536 {
537         struct dentry *parent;
538         int ret;
539 
540         if (IS_ERR_OR_NULL(dentry))
541                 return;
542 
543         parent = dentry->d_parent;
544         if (!parent || !parent->d_inode)
545                 return;
546 
547         inode_lock(parent->d_inode);
548         ret = __tracefs_remove(dentry, parent);
549         inode_unlock(parent->d_inode);
550         if (!ret)
551                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
552 }
553 
554 /**
555  * tracefs_remove_recursive - recursively removes a directory
556  * @dentry: a pointer to a the dentry of the directory to be removed.
557  *
558  * This function recursively removes a directory tree in tracefs that
559  * was previously created with a call to another tracefs function
560  * (like tracefs_create_file() or variants thereof.)
561  */
562 void tracefs_remove_recursive(struct dentry *dentry)
563 {
564         struct dentry *child, *parent;
565 
566         if (IS_ERR_OR_NULL(dentry))
567                 return;
568 
569         parent = dentry->d_parent;
570         if (!parent || !parent->d_inode)
571                 return;
572 
573         parent = dentry;
574  down:
575         inode_lock(parent->d_inode);
576  loop:
577         /*
578          * The parent->d_subdirs is protected by the d_lock. Outside that
579          * lock, the child can be unlinked and set to be freed which can
580          * use the d_u.d_child as the rcu head and corrupt this list.
581          */
582         spin_lock(&parent->d_lock);
583         list_for_each_entry(child, &parent->d_subdirs, d_child) {
584                 if (!simple_positive(child))
585                         continue;
586 
587                 /* perhaps simple_empty(child) makes more sense */
588                 if (!list_empty(&child->d_subdirs)) {
589                         spin_unlock(&parent->d_lock);
590                         inode_unlock(parent->d_inode);
591                         parent = child;
592                         goto down;
593                 }
594 
595                 spin_unlock(&parent->d_lock);
596 
597                 if (!__tracefs_remove(child, parent))
598                         simple_release_fs(&tracefs_mount, &tracefs_mount_count);
599 
600                 /*
601                  * The parent->d_lock protects agaist child from unlinking
602                  * from d_subdirs. When releasing the parent->d_lock we can
603                  * no longer trust that the next pointer is valid.
604                  * Restart the loop. We'll skip this one with the
605                  * simple_positive() check.
606                  */
607                 goto loop;
608         }
609         spin_unlock(&parent->d_lock);
610 
611         inode_unlock(parent->d_inode);
612         child = parent;
613         parent = parent->d_parent;
614         inode_lock(parent->d_inode);
615 
616         if (child != dentry)
617                 /* go up */
618                 goto loop;
619 
620         if (!__tracefs_remove(child, parent))
621                 simple_release_fs(&tracefs_mount, &tracefs_mount_count);
622         inode_unlock(parent->d_inode);
623 }
624 
625 /**
626  * tracefs_initialized - Tells whether tracefs has been registered
627  */
628 bool tracefs_initialized(void)
629 {
630         return tracefs_registered;
631 }
632 
633 static int __init tracefs_init(void)
634 {
635         int retval;
636 
637         retval = sysfs_create_mount_point(kernel_kobj, "tracing");
638         if (retval)
639                 return -EINVAL;
640 
641         retval = register_filesystem(&trace_fs_type);
642         if (!retval)
643                 tracefs_registered = true;
644 
645         return retval;
646 }
647 core_initcall(tracefs_init);
648 

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