传统文件系统，多个目录项集中存放在同一物理块，读取目录项就像读取文件内容一样，物理块内容是连续的目录项，因此目录文件也是有大小区分的，子目录和文件数目越多，那么目录文件尺寸越大。
而ubifs每当增加一个新的目录项，ubifs在master area中生成一个directory entry node，并把这个node插到wandering tree的某个位置，通过wandering tree保持同意目录下目录项在逻辑上的相邻。
这种特性也带来了ubifs在一些目录操作接口上的怪异行为，比如readdir和stat。
78 /**
79 * ubifs_new_inode - allocate new UBIFS inode object.
80 * @c: UBIFS file-system description object
81 * @dir: parent directory inode
82 * @mode: inode mode flags
83 *
84 * This function finds an unused inode number, allocates new inode and
85 * initializes it. Returns new inode in case of success and an error code in
86 * case of failure.
87 */
88 struct inode *ubifs_new_inode(struct ubifs_info *c, const struct inode *dir,
89 int mode)
90 {
91 struct inode *inode;
92 struct ubifs_inode *ui;
93
94 inode = new_inode(c->vfs_sb);
95 ui = ubifs_inode(inode);
96 if (!inode)
97 return ERR_PTR(-ENOMEM);
98
99 /*
100 * Set 'S_NOCMTIME' to prevent VFS form updating [mc]time of inodes and
101 * marking them dirty in file write path (see 'file_update_time()').
102 * UBIFS has to fully control "clean <-> dirty" transitions of inodes
103 * to make budgeting work.
104 */
105 inode->i_flags |= (S_NOCMTIME);
106
107 inode_init_owner(inode, dir, mode);
108 inode->i_mtime = inode->i_atime = inode->i_ctime =
109 ubifs_current_time(inode);
110 inode->i_mapping->nrpages = 0;
111 /* Disable readahead */
112 inode->i_mapping->backing_dev_info = &c->bdi;
113
114 switch (mode & S_IFMT) {
115 case S_IFREG:
116 inode->i_mapping->a_ops = &ubifs_file_address_operations;
117 inode->i_op = &ubifs_file_inode_operations;
118 inode->i_fop = &ubifs_file_operations;
119 break;
120 case S_IFDIR:
121 inode->i_op = &ubifs_dir_inode_operations;
122 inode->i_fop = &ubifs_dir_operations;
123 inode->i_size = ui->ui_size = UBIFS_INO_NODE_SZ;
124 break;
125 case S_IFLNK:
126 inode->i_op = &ubifs_symlink_inode_operations;
127 break;
128 case S_IFSOCK:
129 case S_IFIFO:
130 case S_IFBLK:
131 case S_IFCHR:
132 inode->i_op = &ubifs_file_inode_operations;
133 break;
134 default:
135 BUG();
136 }
137
138 ui->flags = inherit_flags(dir, mode);
139 ubifs_set_inode_flags(inode);
140 if (S_ISREG(mode))
141 ui->compr_type = c->default_compr;
142 else
143 ui->compr_type = UBIFS_COMPR_NONE;
144 ui->synced_i_size = 0;
145
146 spin_lock(&c->cnt_lock);
147 /* Inode number overflow is currently not supported */
148 if (c->highest_inum >= INUM_WARN_WATERMARK) {
149 if (c->highest_inum >= INUM_WATERMARK) {
150 spin_unlock(&c->cnt_lock);
151 ubifs_err("out of inode numbers");
152 make_bad_inode(inode);
153 iput(inode);
154 return ERR_PTR(-EINVAL);
155 }
156 ubifs_warn("running out of inode numbers (current %lu, max %d)",
157 (unsigned long)c->highest_inum, INUM_WATERMARK);
158 }
159
160 inode->i_ino = ++c->highest_inum;
161 /*
162 * The creation sequence number remains with this inode for its
163 * lifetime. All nodes for this inode have a greater sequence number,
164 * and so it is possible to distinguish obsolete nodes belonging to a
165 * previous incarnation of the same inode number - for example, for the
166 * purpose of rebuilding the index.
167 */
168 ui->creat_sqnum = ++c->max_sqnum;
169 spin_unlock(&c->cnt_lock);
170 return inode;
171 }
138 ~ 139 UBIFS有些inode flag是可以从父目录继承到子目录项的，比如UBIFS_COMPR_FL, UBIFS_SYNC_FL以及UBIFS_DIRSYNC_FL.
UBIFS_COMPR_FL是compression打开关闭标记
UBIFS_SYNC_FL是文件同步标记
UBIFS_DIRSYNC_FL是 是目录内容修改同步标记，这个标记只有子目录项还是目录时才会继承
147～160 UBIFS使用highest_inum记录已经使用过的inode number的最大值，UBIFS使用过的ino不能重复使用
168 creat_sqnum记录这个inode的sequence number，在unclean unmount发生时，ubifs可以通过这个sequence number来确定哪个inode是最新的.
192 static struct dentry *ubifs_lookup(struct inode *dir, struct dentry *dentry,
193 struct nameidata *nd)
194 {
195 int err;
196 union ubifs_key key;
197 struct inode *inode = NULL;
198 struct ubifs_dent_node *dent;
199 struct ubifs_info *c = dir->i_sb->s_fs_info;
200
201 dbg_gen("'%.*s' in dir ino %lu",
202 dentry->d_name.len, dentry->d_name.name, dir->i_ino);
203
204 if (dentry->d_name.len > UBIFS_MAX_NLEN)
205 return ERR_PTR(-ENAMETOOLONG);
206
207 dent = kmalloc(UBIFS_MAX_DENT_NODE_SZ, GFP_NOFS);
208 if (!dent)
209 return ERR_PTR(-ENOMEM);
210
211 dent_key_init(c, &key, dir->i_ino, &dentry->d_name);
212
213 err = ubifs_tnc_lookup_nm(c, &key, dent, &dentry->d_name);
214 if (err) {
215 if (err == -ENOENT) {
216 dbg_gen("not found");
217 goto done;
218 }
219 goto out;
220 }
221
222 if (dbg_check_name(dent, &dentry->d_name)) {
223 err = -EINVAL;
224 goto out;
225 }
226
227 inode = ubifs_iget(dir->i_sb, le64_to_cpu(dent->inum));
228 if (IS_ERR(inode)) {
229 /*
230 * This should not happen. Probably the file-system needs
231 * checking.
232 */
233 err = PTR_ERR(inode);
234 ubifs_err("dead directory entry '%.*s', error %d",
235 dentry->d_name.len, dentry->d_name.name, err);
236 ubifs_ro_mode(c, err);
237 goto out;
238 }
239
240 done:
241 kfree(dent);
242 /*
243 * Note, d_splice_alias() would be required instead if we supported
244 * NFS.
245 */
246 d_add(dentry, inode);
247 return NULL;
248
249 out:
250 kfree(dent);
251 return ERR_PTR(err);
252 }
211 ~ 213 生成目录项的key，然后在tnc tree中查找符合这个key的node, dentry node可能已经在tnc中，那么直接返回就可以了，如果没在tnc中，则会从flash读取并加到tnc
247 不知道为什么成功了也返回NULL
254 static int ubifs_create(struct inode *dir, struct dentry *dentry, int mode,
255 struct nameidata *nd)
256 {
257 struct inode *inode;
258 struct ubifs_info *c = dir->i_sb->s_fs_info;
259 int err, sz_change = CALC_DENT_SIZE(dentry->d_name.len);
260 struct ubifs_budget_req req = { .new_ino = 1, .new_dent = 1,
261 .dirtied_ino = 1 };
262 struct ubifs_inode *dir_ui = ubifs_inode(dir);
263
264 /*
265 * Budget request settings: new inode, new direntry, changing the
266 * parent directory inode.
267 */
268
269 dbg_gen("dent '%.*s', mode %#x in dir ino %lu",
270 dentry->d_name.len, dentry->d_name.name, mode, dir->i_ino);
271
272 err = ubifs_budget_space(c, &req);
273 if (err)
274 return err;
275
276 inode = ubifs_new_inode(c, dir, mode);
277 if (IS_ERR(inode)) {
278 err = PTR_ERR(inode);
279 goto out_budg;
280 }
281
282 mutex_lock(&dir_ui->ui_mutex);
283 dir->i_size += sz_change;
284 dir_ui->ui_size = dir->i_size;
285 dir->i_mtime = dir->i_ctime = inode->i_ctime;
286 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
287 if (err)
288 goto out_cancel;
289 mutex_unlock(&dir_ui->ui_mutex);
290
291 ubifs_release_budget(c, &req);
292 insert_inode_hash(inode);
293 d_instantiate(dentry, inode);
294 return 0;
295
296 out_cancel:
297 dir->i_size -= sz_change;
298 dir_ui->ui_size = dir->i_size;
299 mutex_unlock(&dir_ui->ui_mutex);
300 make_bad_inode(inode);
301 iput(inode);
302 out_budg:
303 ubifs_release_budget(c, &req);
304 ubifs_err("cannot create regular file, error %d", err);
305 return err;
306 }
在调用ubifs_create前，已经创建了这个文件对应的dentry，但是相应的inode以及目录项还不存在
272 确保足够的空间进行下面的操作, 创建一个文件节点需要修改:parent inode的ctime和size, 新文件的inode和新文件对应的目录项
286 ubifs_jnl_update写新目录项，inode以及parent inode到journal
338 /*
339 * The classical Unix view for directory is that it is a linear array of
340 * (name, inode number) entries. Linux/VFS assumes this model as well.
341 * Particularly, 'readdir()' call wants us to return a directory entry offset
342 * which later may be used to continue 'readdir()'ing the directory or to
343 * 'seek()' to that specific direntry. Obviously UBIFS does not really fit this
344 * model because directory entries are identified by keys, which may collide.
345 *
346 * UBIFS uses directory entry hash value for directory offsets, so
347 * 'seekdir()'/'telldir()' may not always work because of possible key
348 * collisions. But UBIFS guarantees that consecutive 'readdir()' calls work
349 * properly by means of saving full directory entry name in the private field
350 * of the file description object.
351 *
352 * This means that UBIFS cannot support NFS which requires full
353 * 'seekdir()'/'telldir()' support.
354 */
355 static int ubifs_readdir(struct file *file, void *dirent, filldir_t filldir)
356 {
357 int err, over = 0;
358 struct qstr nm;
359 union ubifs_key key;
360 struct ubifs_dent_node *dent;
361 struct inode *dir = file->f_path.dentry->d_inode;
362 struct ubifs_info *c = dir->i_sb->s_fs_info;
363
364 dbg_gen("dir ino %lu, f_pos %#llx", dir->i_ino, file->f_pos);
365
366 if (file->f_pos > UBIFS_S_KEY_HASH_MASK || file->f_pos == 2)
367 /*
368 * The directory was seek'ed to a senseless position or there
369 * are no more entries.
370 */
371 return 0;
372
373 /* File positions 0 and 1 correspond to "." and ".." */
374 if (file->f_pos == 0) {
375 ubifs_assert(!file->private_data);
376 over = filldir(dirent, ".", 1, 0, dir->i_ino, DT_DIR);
377 if (over)
378 return 0;
379 file->f_pos = 1;
380 }
381
382 if (file->f_pos == 1) {
383 ubifs_assert(!file->private_data);
384 over = filldir(dirent, "..", 2, 1,
385 parent_ino(file->f_path.dentry), DT_DIR);
386 if (over)
387 return 0;
388
389 /* Find the first entry in TNC and save it */
390 lowest_dent_key(c, &key, dir->i_ino);
391 nm.name = NULL;
392 dent = ubifs_tnc_next_ent(c, &key, &nm);
393 if (IS_ERR(dent)) {
394 err = PTR_ERR(dent);
395 goto out;
396 }
397
398 file->f_pos = key_hash_flash(c, &dent->key);
399 file->private_data = dent;
400 }
401
402 dent = file->private_data;
403 if (!dent) {
404 /*
405 * The directory was seek'ed to and is now readdir'ed.
406 * Find the entry corresponding to @file->f_pos or the
407 * closest one.
408 */
409 dent_key_init_hash(c, &key, dir->i_ino, file->f_pos);
410 nm.name = NULL;
411 dent = ubifs_tnc_next_ent(c, &key, &nm);
412 if (IS_ERR(dent)) {
413 err = PTR_ERR(dent);
414 goto out;
415 }
416 file->f_pos = key_hash_flash(c, &dent->key);
417 file->private_data = dent;
418 }
419
420 while (1) {
421 dbg_gen("feed '%s', ino %llu, new f_pos %#x",
422 dent->name, (unsigned long long)le64_to_cpu(dent->inum),
423 key_hash_flash(c, &dent->key));
424 ubifs_assert(le64_to_cpu(dent->ch.sqnum) >
425 ubifs_inode(dir)->creat_sqnum);
426
427 nm.len = le16_to_cpu(dent->nlen);
428 over = filldir(dirent, dent->name, nm.len, file->f_pos,
429 le64_to_cpu(dent->inum),
430 vfs_dent_type(dent->type));
431 if (over)
432 return 0;
433
434 /* Switch to the next entry */
435 key_read(c, &dent->key, &key);
436 nm.name = dent->name;
437 dent = ubifs_tnc_next_ent(c, &key, &nm);
438 if (IS_ERR(dent)) {
439 err = PTR_ERR(dent);
440 goto out;
441 }
442
443 kfree(file->private_data);
444 file->f_pos = key_hash_flash(c, &dent->key);
445 file->private_data = dent;
446 cond_resched();
447 }
448
449 out:
450 if (err != -ENOENT) {
451 ubifs_err("cannot find next direntry, error %d", err);
452 return err;
453 }
454
455 kfree(file->private_data);
456 file->private_data = NULL;
457 file->f_pos = 2;
458 return 0;
459 }
ubifs_readdir 读取目录@file下的目录项，内容放入@dirent，每读取一个目录项，由filldir填充@dirent，具体读取多少，由filldir的返回值决定
ubifs_readdir的问题是offset并不像传统文件系统的offset一样，因为ubifs的目录项并不是顺序排放的，dentry node没有offset，而是由key来决定在父目录中的排序位置。
从代码中可以看到，只有"."和".."目录项offset是传统的位置，其他目录项的offset就是名字的hash值
374 ~ 387 读取. 和..目录项
389 ~ 399 读取第一个目录项
403 ~ 418 由于读取的offset并不是常规的offset, 所以找一个最接近这个offset的目录项
420 ～477 ubifs_tnc_next_ent依次遍历所有的entry，直到filldir请求结束遍历
461 /* If a directory is seeked, we have to free saved readdir() state */
462 static loff_t ubifs_dir_llseek(struct file *file, loff_t offset, int origin)
463 {
464 kfree(file->private_data);
465 file->private_data = NULL;
466 return generic_file_llseek(file, offset, origin);
467 }
465 由于ubifs借用来file->private_data来模拟offset，所以llseek要先清空private_data,具体参见ubifs_readdir
static int ubifs_link(struct dentry *old_dentry, struct inode *dir,
504 struct dentry *dentry)
505 {
506 struct ubifs_info *c = dir->i_sb->s_fs_info;
507 struct inode *inode = old_dentry->d_inode;
508 struct ubifs_inode *ui = ubifs_inode(inode);
509 struct ubifs_inode *dir_ui = ubifs_inode(dir);
510 int err, sz_change = CALC_DENT_SIZE(dentry->d_name.len);
511 struct ubifs_budget_req req = { .new_dent = 1, .dirtied_ino = 2,
512 .dirtied_ino_d = ALIGN(ui->data_len, 8) };
513
514 /*
515 * Budget request settings: new direntry, changing the target inode,
516 * changing the parent inode.
517 */
518
519 dbg_gen("dent '%.*s' to ino %lu (nlink %d) in dir ino %lu",
520 dentry->d_name.len, dentry->d_name.name, inode->i_ino,
521 inode->i_nlink, dir->i_ino);
522 ubifs_assert(mutex_is_locked(&dir->i_mutex));
523 ubifs_assert(mutex_is_locked(&inode->i_mutex));
524
525 /*
526 * Return -ENOENT if we've raced with unlink and i_nlink is 0. Doing
527 * otherwise has the potential to corrupt the orphan inode list.
528 *
529 * Indeed, consider a scenario when 'vfs_link(dirA/fileA)' and
530 * 'vfs_unlink(dirA/fileA, dirB/fileB)' race. 'vfs_link()' does not
531 * lock 'dirA->i_mutex', so this is possible. Both of the functions
532 * lock 'fileA->i_mutex' though. Suppose 'vfs_unlink()' wins, and takes
533 * 'fileA->i_mutex' mutex first. Suppose 'fileA->i_nlink' is 1. In this
534 * case 'ubifs_unlink()' will drop the last reference, and put 'inodeA'
535 * to the list of orphans. After this, 'vfs_link()' will link
536 * 'dirB/fileB' to 'inodeA'. This is a problem because, for example,
537 * the subsequent 'vfs_unlink(dirB/fileB)' will add the same inode
538 * to the list of orphans.
539 */
540 if (inode->i_nlink == 0)
541 return -ENOENT;
542
543 err = dbg_check_synced_i_size(inode);
544 if (err)
545 return err;
546
547 err = ubifs_budget_space(c, &req);
548 if (err)
549 return err;
550
551 lock_2_inodes(dir, inode);
552 inc_nlink(inode);
554 inode->i_ctime = ubifs_current_time(inode);
555 dir->i_size += sz_change;
556 dir_ui->ui_size = dir->i_size;
557 dir->i_mtime = dir->i_ctime = inode->i_ctime;
558 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
559 if (err)
560 goto out_cancel;
561 unlock_2_inodes(dir, inode);
562
563 ubifs_release_budget(c, &req);
564 d_instantiate(dentry, inode);
565 return 0;
566
567 out_cancel:
568 dir->i_size -= sz_change;
569 dir_ui->ui_size = dir->i_size;
570 drop_nlink(inode);
571 unlock_2_inodes(dir, inode);
572 ubifs_release_budget(c, &req);
573 iput(inode);
574 return err;
575 }
ubifs_link用来把@old_dentry对应的文件，链接到@dentry这个目录项上，是文件系统硬链接的底层实现
ubifs_link和ubifs_create类似，都会修改parent inode，增加一个新的目录项。
ubifs_link不需要创建inode，因为inode已经存在了，但是需要修改inode的link和修改inode的ctime
552 增加inode的nlink，因为一个新的dentry指向了这个文件
577 static int ubifs_unlink(struct inode *dir, struct dentry *dentry)
578 {
579 struct ubifs_info *c = dir->i_sb->s_fs_info;
580 struct inode *inode = dentry->d_inode;
581 struct ubifs_inode *dir_ui = ubifs_inode(dir);
582 int sz_change = CALC_DENT_SIZE(dentry->d_name.len);
583 int err, budgeted = 1;
584 struct ubifs_budget_req req = { .mod_dent = 1, .dirtied_ino = 2 };
585
586 /*
587 * Budget request settings: deletion direntry, deletion inode (+1 for
588 * @dirtied_ino), changing the parent directory inode. If budgeting
589 * fails, go ahead anyway because we have extra space reserved for
590 * deletions.
591 */
592
593 dbg_gen("dent '%.*s' from ino %lu (nlink %d) in dir ino %lu",
594 dentry->d_name.len, dentry->d_name.name, inode->i_ino,
595 inode->i_nlink, dir->i_ino);
596 ubifs_assert(mutex_is_locked(&dir->i_mutex));
597 ubifs_assert(mutex_is_locked(&inode->i_mutex));
598 err = dbg_check_synced_i_size(inode);
599 if (err)
600 return err;
601
602 err = ubifs_budget_space(c, &req);
603 if (err) {
604 if (err != -ENOSPC)
605 return err;
606 budgeted = 0;
607 }
608
609 lock_2_inodes(dir, inode);
610 inode->i_ctime = ubifs_current_time(dir);
611 drop_nlink(inode);
612 dir->i_size -= sz_change;
613 dir_ui->ui_size = dir->i_size;
614 dir->i_mtime = dir->i_ctime = inode->i_ctime;
615 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 1, 0);
616 if (err)
617 goto out_cancel;
618 unlock_2_inodes(dir, inode);
619
620 if (budgeted)
621 ubifs_release_budget(c, &req);
622 else {
623 /* We've deleted something - clean the "no space" flags */
624 c->nospace = c->nospace_rp = 0;
625 smp_wmb();
626 }
627 return 0;
628
629 out_cancel:
630 dir->i_size += sz_change;
631 dir_ui->ui_size = dir->i_size;
632 inc_nlink(inode);
633 unlock_2_inodes(dir, inode);
634 if (budgeted)
635 ubifs_release_budget(c, &req);
636 return err;
637 }
ubifs_unlink是ubifs_link的逆操作，把@dentry目录项从@dir中删除掉
这个操作涉及到一个目录项的删除，以及parent inode和child inode的修改
611 由于少了一个到child inode的目录项, 减少child inode的链接数
612 由于删除了目录项，父目录inode的尺寸减去目录项node的尺寸
615 ubifs_jnl_update第五个参数1 用来指定对目录项的删除
639 /**
640 * check_dir_empty - check if a directory is empty or not.
641 * @c: UBIFS file-system description object
642 * @dir: VFS inode object of the directory to check
643 *
644 * This function checks if directory @dir is empty. Returns zero if the
645 * directory is empty, %-ENOTEMPTY if it is not, and other negative error codes
646 * in case of of errors.
647 */
648 static int check_dir_empty(struct ubifs_info *c, struct inode *dir)
649 {
650 struct qstr nm = { .name = NULL };
651 struct ubifs_dent_node *dent;
652 union ubifs_key key;
653 int err;
654
655 lowest_dent_key(c, &key, dir->i_ino);
656 dent = ubifs_tnc_next_ent(c, &key, &nm);
657 if (IS_ERR(dent)) {
658 err = PTR_ERR(dent);
659 if (err == -ENOENT)
660 err = 0;
661 } else {
662 kfree(dent);
663 err = -ENOTEMPTY;
664 }
665 return err;
666 }
这个函数检测给定的目录@dir是否为空
655 首先计算出这个目录下最小的dentry key
656 ubifs_tnc_next_ent 找到并返回@key后面的一个目录项，如果不存在，说明没有目录项，否则有
668 static int ubifs_rmdir(struct inode *dir, struct dentry *dentry)
669 {
670 struct ubifs_info *c = dir->i_sb->s_fs_info;
671 struct inode *inode = dentry->d_inode;
672 int sz_change = CALC_DENT_SIZE(dentry->d_name.len);
673 int err, budgeted = 1;
674 struct ubifs_inode *dir_ui = ubifs_inode(dir);
675 struct ubifs_budget_req req = { .mod_dent = 1, .dirtied_ino = 2 };
676
677 /*
678 * Budget request settings: deletion direntry, deletion inode and
679 * changing the parent inode. If budgeting fails, go ahead anyway
680 * because we have extra space reserved for deletions.
681 */
682
683 dbg_gen("directory '%.*s', ino %lu in dir ino %lu", dentry->d_name.len,
684 dentry->d_name.name, inode->i_ino, dir->i_ino);
685 ubifs_assert(mutex_is_locked(&dir->i_mutex));
686 ubifs_assert(mutex_is_locked(&inode->i_mutex));
687 err = check_dir_empty(c, dentry->d_inode);
688 if (err)
689 return err;
690
691 err = ubifs_budget_space(c, &req);
692 if (err) {
693 if (err != -ENOSPC)
694 return err;
695 budgeted = 0;
696 }
697
698 lock_2_inodes(dir, inode);
699 inode->i_ctime = ubifs_current_time(dir);
700 clear_nlink(inode);
701 drop_nlink(dir);
702 dir->i_size -= sz_change;
703 dir_ui->ui_size = dir->i_size;
704 dir->i_mtime = dir->i_ctime = inode->i_ctime;
705 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 1, 0);
706 if (err)
707 goto out_cancel;
708 unlock_2_inodes(dir, inode);
709
710 if (budgeted)
711 ubifs_release_budget(c, &req);
712 else {
713 /* We've deleted something - clean the "no space" flags */
714 c->nospace = c->nospace_rp = 0;
715 smp_wmb();
716 }
717 return 0;
718
719 out_cancel:
720 dir->i_size += sz_change;
721 dir_ui->ui_size = dir->i_size;
722 inc_nlink(dir);
723 inc_nlink(inode);
724 inc_nlink(inode);
725 unlock_2_inodes(dir, inode);
726 if (budgeted)
727 ubifs_release_budget(c, &req);
728 return err;
729 }
ubifs_rmdir删除@dir下的目录项@dentry，这个函数和ubifs_unlink的区别是前者删除的是子目录，后者删除的是非子目录
677 ~ 681 该操作涉及到删除目录项，删除子目录的inode，更改父目录的inode
687 判断待删除目录是否包含除"." ".."外的目录项，非空目录是不能删除的。
700 clear_nlink直接设置inode的nlink为0，事实上我觉得使用drop_nlink也可
701 减少父目录inode的nlink
731 static int ubifs_mkdir(struct inode *dir, struct dentry *dentry, int mode)
732 {
733 struct inode *inode;
734 struct ubifs_inode *dir_ui = ubifs_inode(dir);
735 struct ubifs_info *c = dir->i_sb->s_fs_info;
736 int err, sz_change = CALC_DENT_SIZE(dentry->d_name.len);
737 struct ubifs_budget_req req = { .new_ino = 1, .new_dent = 1 };
738
739 /*
740 * Budget request settings: new inode, new direntry and changing parent
741 * directory inode.
742 */
743
744 dbg_gen("dent '%.*s', mode %#x in dir ino %lu",
745 dentry->d_name.len, dentry->d_name.name, mode, dir->i_ino);
746
747 err = ubifs_budget_space(c, &req);
748 if (err)
749 return err;
750
751 inode = ubifs_new_inode(c, dir, S_IFDIR | mode);
752 if (IS_ERR(inode)) {
753 err = PTR_ERR(inode);
754 goto out_budg;
755 }
756
757 mutex_lock(&dir_ui->ui_mutex);
758 insert_inode_hash(inode);
759 inc_nlink(inode);
760 inc_nlink(dir);
761 dir->i_size += sz_change;
762 dir_ui->ui_size = dir->i_size;
763 dir->i_mtime = dir->i_ctime = inode->i_ctime;
764 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
765 if (err) {
766 ubifs_err("cannot create directory, error %d", err);
767 goto out_cancel;
768 }
769 mutex_unlock(&dir_ui->ui_mutex);
770
771 ubifs_release_budget(c, &req);
772 d_instantiate(dentry, inode);
773 return 0;
774
775 out_cancel:
776 dir->i_size -= sz_change;
777 dir_ui->ui_size = dir->i_size;
778 drop_nlink(dir);
779 mutex_unlock(&dir_ui->ui_mutex);
780 make_bad_inode(inode);
781 iput(inode);
782 out_budg:
783 ubifs_release_budget(c, &req);
784 return err;
785 }
ubifs_mkdir 在父目录@dir下创建@dentry对应的子目录，该函数需要分配子目录的inode
ubifs涉及到新目录项的添加，子inode的创建以及父inode的修改
751 为子目录创建inode
758 把新创建的inode加到hash table中
759 ~ 760 增加父子inode的nlink
772 把dentry和新创建的inode关联起来
787 static int ubifs_mknod(struct inode *dir, struct dentry *dentry,
788 int mode, dev_t rdev)
789 {
790 struct inode *inode;
791 struct ubifs_inode *ui;
792 struct ubifs_inode *dir_ui = ubifs_inode(dir);
793 struct ubifs_info *c = dir->i_sb->s_fs_info;
794 union ubifs_dev_desc *dev = NULL;
795 int sz_change = CALC_DENT_SIZE(dentry->d_name.len);
796 int err, devlen = 0;
797 struct ubifs_budget_req req = { .new_ino = 1, .new_dent = 1,
798 .new_ino_d = ALIGN(devlen, 8),
799 .dirtied_ino = 1 };
800
801 /*
802 * Budget request settings: new inode, new direntry and changing parent
803 * directory inode.
804 */
805
806 dbg_gen("dent '%.*s' in dir ino %lu",
807 dentry->d_name.len, dentry->d_name.name, dir->i_ino);
808
809 if (!new_valid_dev(rdev))
810 return -EINVAL;
811
812 if (S_ISBLK(mode) || S_ISCHR(mode)) {
813 dev = kmalloc(sizeof(union ubifs_dev_desc), GFP_NOFS);
814 if (!dev)
815 return -ENOMEM;
816 devlen = ubifs_encode_dev(dev, rdev);
817 }
818
819 err = ubifs_budget_space(c, &req);
820 if (err) {
821 kfree(dev);
822 return err;
823 }
824
825 inode = ubifs_new_inode(c, dir, mode);
826 if (IS_ERR(inode)) {
827 kfree(dev);
828 err = PTR_ERR(inode);
829 goto out_budg;
830 }
831
832 init_special_inode(inode, inode->i_mode, rdev);
833 inode->i_size = ubifs_inode(inode)->ui_size = devlen;
834 ui = ubifs_inode(inode);
835 ui->data = dev;
836 ui->data_len = devlen;
837
838 mutex_lock(&dir_ui->ui_mutex);
839 dir->i_size += sz_change;
840 dir_ui->ui_size = dir->i_size;
841 dir->i_mtime = dir->i_ctime = inode->i_ctime;
842 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
843 if (err)
844 goto out_cancel;
845 mutex_unlock(&dir_ui->ui_mutex);
846
847 ubifs_release_budget(c, &req);
848 insert_inode_hash(inode);
849 d_instantiate(dentry, inode);
850 return 0;
851
852 out_cancel:
853 dir->i_size -= sz_change;
854 dir_ui->ui_size = dir->i_size;
855 mutex_unlock(&dir_ui->ui_mutex);
856 make_bad_inode(inode);
857 iput(inode);
858 out_budg:
859 ubifs_release_budget(c, &req);
860 return err;
861 }
ubifs_mknod和ubifs_mkdir非常类似，只是前者创建的是设备节点而后者创建的是子目录，ubifs_mknod不会增加父母录的连接数
863 static int ubifs_symlink(struct inode *dir, struct dentry *dentry,
864 const char *symname)
865 {
866 struct inode *inode;
867 struct ubifs_inode *ui;
868 struct ubifs_inode *dir_ui = ubifs_inode(dir);
869 struct ubifs_info *c = dir->i_sb->s_fs_info;
870 int err, len = strlen(symname);
871 int sz_change = CALC_DENT_SIZE(dentry->d_name.len);
872 struct ubifs_budget_req req = { .new_ino = 1, .new_dent = 1,
873 .new_ino_d = ALIGN(len, 8),
874 .dirtied_ino = 1 };
875
876 /*
877 * Budget request settings: new inode, new direntry and changing parent
878 * directory inode.
879 */
880
881 dbg_gen("dent '%.*s', target '%s' in dir ino %lu", dentry->d_name.len,
882 dentry->d_name.name, symname, dir->i_ino);
883
884 if (len > UBIFS_MAX_INO_DATA)
885 return -ENAMETOOLONG;
886
887 err = ubifs_budget_space(c, &req);
888 if (err)
889 return err;
890
891 inode = ubifs_new_inode(c, dir, S_IFLNK | S_IRWXUGO);
892 if (IS_ERR(inode)) {
893 err = PTR_ERR(inode);
894 goto out_budg;
895 }
896
897 ui = ubifs_inode(inode);
898 ui->data = kmalloc(len + 1, GFP_NOFS);
899 if (!ui->data) {
900 err = -ENOMEM;
901 goto out_inode;
902 }
903
904 memcpy(ui->data, symname, len);
905 ((char *)ui->data)[len] = '\0';
906 /*
907 * The terminating zero byte is not written to the flash media and it
908 * is put just to make later in-memory string processing simpler. Thus,
909 * data length is @len, not @len + %1.
910 */
911 ui->data_len = len;
912 inode->i_size = ubifs_inode(inode)->ui_size = len;
913
914 mutex_lock(&dir_ui->ui_mutex);
915 dir->i_size += sz_change;
916 dir_ui->ui_size = dir->i_size;
917 dir->i_mtime = dir->i_ctime = inode->i_ctime;
918 err = ubifs_jnl_update(c, dir, &dentry->d_name, inode, 0, 0);
919 if (err)
920 goto out_cancel;
921 mutex_unlock(&dir_ui->ui_mutex);
922
923 ubifs_release_budget(c, &req);
924 insert_inode_hash(inode);
925 d_instantiate(dentry, inode);
926 return 0;
927
928 out_cancel:
929 dir->i_size -= sz_change;
930 dir_ui->ui_size = dir->i_size;
931 mutex_unlock(&dir_ui->ui_mutex);
932 out_inode:
933 make_bad_inode(inode);
934 iput(inode);
935 out_budg:
936 ubifs_release_budget(c, &req);
937 return err;
938 }
ubifs_symlink在父目录@dir下增加@dentry指定的目录项，这个函数需要创建一个新的inode，增加一个新的目录项，修改parent inode
新创建的inode数据内容为@symname指定的路径，放在ui->data内，由ui->data_len指定长度
该函数不增加parent inode和child inode的nlink
884 该行限制了符号链接的最大长度不能超过UBIFS_MAX_INO_DATA，注意这只是存储方面的限制，对symlink名最大长度的限制来自多方面
979 static int ubifs_rename(struct inode *old_dir, struct dentry *old_dentry,
980 struct inode *new_dir, struct dentry *new_dentry)
981 {
982 struct ubifs_info *c = old_dir->i_sb->s_fs_info;
983 struct inode *old_inode = old_dentry->d_inode;
984 struct inode *new_inode = new_dentry->d_inode;
985 struct ubifs_inode *old_inode_ui = ubifs_inode(old_inode);
986 int err, release, sync = 0, move = (new_dir != old_dir);
987 int is_dir = S_ISDIR(old_inode->i_mode);
988 int unlink = !!new_inode;
989 int new_sz = CALC_DENT_SIZE(new_dentry->d_name.len);
990 int old_sz = CALC_DENT_SIZE(old_dentry->d_name.len);
991 struct ubifs_budget_req req = { .new_dent = 1, .mod_dent = 1,
992 .dirtied_ino = 3 };
993 struct ubifs_budget_req ino_req = { .dirtied_ino = 1,
994 .dirtied_ino_d = ALIGN(old_inode_ui->data_len, 8) };
995 struct timespec time;
996
997 /*
998 * Budget request settings: deletion direntry, new direntry, removing
999 * the old inode, and changing old and new parent directory inodes.
1000 *
1001 * However, this operation also marks the target inode as dirty and
1002 * does not write it, so we allocate budget for the target inode
1003 * separately.
1004 */
1005
1006 dbg_gen("dent '%.*s' ino %lu in dir ino %lu to dent '%.*s' in "
1007 "dir ino %lu", old_dentry->d_name.len, old_dentry->d_name.name,
1008 old_inode->i_ino, old_dir->i_ino, new_dentry->d_name.len,
1009 new_dentry->d_name.name, new_dir->i_ino);
1010 ubifs_assert(mutex_is_locked(&old_dir->i_mutex));
1011 ubifs_assert(mutex_is_locked(&new_dir->i_mutex));
1012 if (unlink)
1013 ubifs_assert(mutex_is_locked(&new_inode->i_mutex));
1014
1015
1016 if (unlink && is_dir) {
1017 err = check_dir_empty(c, new_inode);
1018 if (err)
1019 return err;
1020 }
1021
1022 err = ubifs_budget_space(c, &req);
1023 if (err)
1024 return err;
1025 err = ubifs_budget_space(c, &ino_req);
1026 if (err) {
1027 ubifs_release_budget(c, &req);
1028 return err;
1029 }
1030
1031 lock_3_inodes(old_dir, new_dir, new_inode);
1032
1033 /*
1034 * Like most other Unix systems, set the @i_ctime for inodes on a
1035 * rename.
1036 */
1037 time = ubifs_current_time(old_dir);
1038 old_inode->i_ctime = time;
1039
1040 /* We must adjust parent link count when renaming directories */
1041 if (is_dir) {
1042 if (move) {
1043 /*
1044 * @old_dir loses a link because we are moving
1045 * @old_inode to a different directory.
1046 */
1047 drop_nlink(old_dir);
1048 /*
1049 * @new_dir only gains a link if we are not also
1050 * overwriting an existing directory.
1051 */
1052 if (!unlink)
1053 inc_nlink(new_dir);
1054 } else {
1055 /*
1056 * @old_inode is not moving to a different directory,
1057 * but @old_dir still loses a link if we are
1058 * overwriting an existing directory.
1059 */
1060 if (unlink)
1061 drop_nlink(old_dir);
1062 }
1063 }
1064
1065 old_dir->i_size -= old_sz;
1066 ubifs_inode(old_dir)->ui_size = old_dir->i_size;
1067 old_dir->i_mtime = old_dir->i_ctime = time;
1068 new_dir->i_mtime = new_dir->i_ctime = time;
1069
1070 /*
1071 * And finally, if we unlinked a direntry which happened to have the
1072 * same name as the moved direntry, we have to decrement @i_nlink of
1073 * the unlinked inode and change its ctime.
1074 */
1075 if (unlink) {
1076 /*
1077 * Directories cannot have hard-links, so if this is a
1078 * directory, decrement its @i_nlink twice because an empty
1079 * directory has @i_nlink 2.
1080 */
1081 if (is_dir)
1082 drop_nlink(new_inode);
1083 new_inode->i_ctime = time;
1084 drop_nlink(new_inode);
1085 } else {
1086 new_dir->i_size += new_sz;
1087 ubifs_inode(new_dir)->ui_size = new_dir->i_size;
1088 }
1089
1090 /*
1091 * Do not ask 'ubifs_jnl_rename()' to flush write-buffer if @old_inode
1092 * is dirty, because this will be done later on at the end of
1093 * 'ubifs_rename()'.
1094 */
1095 if (IS_SYNC(old_inode)) {
1096 sync = IS_DIRSYNC(old_dir) || IS_DIRSYNC(new_dir);
1097 if (unlink && IS_SYNC(new_inode))
1098 sync = 1;
1099 }
1100 err = ubifs_jnl_rename(c, old_dir, old_dentry, new_dir, new_dentry,
1101 sync);
1102 if (err)
1103 goto out_cancel;
1104
1105 unlock_3_inodes(old_dir, new_dir, new_inode);
1106 ubifs_release_budget(c, &req);
1107
1108 mutex_lock(&old_inode_ui->ui_mutex);
1109 release = old_inode_ui->dirty;
1110 mark_inode_dirty_sync(old_inode);
1111 mutex_unlock(&old_inode_ui->ui_mutex);
1112
1113 if (release)
1114 ubifs_release_budget(c, &ino_req);
1115 if (IS_SYNC(old_inode))
1116 err = old_inode->i_sb->s_op->write_inode(old_inode, NULL);
1117 return err;
1118
1119 out_cancel:
1120 if (unlink) {
1121 if (is_dir)
1122 inc_nlink(new_inode);
1123 inc_nlink(new_inode);
1124 } else {
1125 new_dir->i_size -= new_sz;
1126 ubifs_inode(new_dir)->ui_size = new_dir->i_size;
1127 }
1128 old_dir->i_size += old_sz;
1129 ubifs_inode(old_dir)->ui_size = old_dir->i_size;
1130 if (is_dir) {
1131 if (move) {
1132 inc_nlink(old_dir);
1133 if (!unlink)
1134 drop_nlink(new_dir);
1135 } else {
1136 if (unlink)
1137 inc_nlink(old_dir);
1138 }
1139 }
1140 unlock_3_inodes(old_dir, new_dir, new_inode);
1141 ubifs_release_budget(c, &ino_req);
1142 ubifs_release_budget(c, &req);
1143 return err;
1144 }
ubifs_rename 重命名@old_dentry为@new_dentry，@old_dir为原目录，@new_dir为新目录
注意@new_dentry可能在改名前就对应着一个文件或目录，因此改名后相当于减少了这个inode的nlink
984 new_inode可能为空或者不为空，为空表明这个文件名原本就不存在，处理起来要简单一些；不为空，表明这个文件名原来就存在，那么rename会覆盖掉@new_dentry原来指向的文件。
1016 ~ 1020 ubifs要求@new_dentry不能对应一个不为空的目录，即rename禁止非空目录覆盖
1041 ~ 1042 is_dir表示@new_dentry是一个目录，move表明old_dir new_dir不是相同的目录（跨目录rename）
1043 ~ 1061 处理nlink
1065 ~ 1068 修改@old_dir的尺寸
1070 ~ 1088 如果@new_dentry本来就对应着一个文件或目录，如果是目录nlink -= 2来释放这个目录inode(前面已经确保这个目录肯定为空)；如果是文件，只需-1
rename 看起来稍微复杂，主要有以下几种分支情况需要仔细处理
1. old_dir new_dir是不是同一个目录
2. new_dentry, old_dentry是不是同一个路径
3. new_dentry old_dentry是目录还是文件
1146 int ubifs_getattr(struct vfsmount *mnt, struct dentry *dentry,
1147 struct kstat *stat)
1148 {
1149 loff_t size;
1150 struct inode *inode = dentry->d_inode;
1151 struct ubifs_inode *ui = ubifs_inode(inode);
1152
1153 mutex_lock(&ui->ui_mutex);
1154 stat->dev = inode->i_sb->s_dev;
1155 stat->ino = inode->i_ino;
1156 stat->mode = inode->i_mode;
1157 stat->nlink = inode->i_nlink;
1158 stat->uid = inode->i_uid;
1159 stat->gid = inode->i_gid;
1160 stat->rdev = inode->i_rdev;
1161 stat->atime = inode->i_atime;
1162 stat->mtime = inode->i_mtime;
1163 stat->ctime = inode->i_ctime;
1164 stat->blksize = UBIFS_BLOCK_SIZE;
1165 stat->size = ui->ui_size;
1166
1167 /*
1168 * Unfortunately, the 'stat()' system call was designed for block
1169 * device based file systems, and it is not appropriate for UBIFS,
1170 * because UBIFS does not have notion of "block". For example, it is
1171 * difficult to tell how many block a directory takes - it actually
1172 * takes less than 300 bytes, but we have to round it to block size,
1173 * which introduces large mistake. This makes utilities like 'du' to
1174 * report completely senseless numbers. This is the reason why UBIFS
1175 * goes the same way as JFFS2 - it reports zero blocks for everything
1176 * but regular files, which makes more sense than reporting completely
1177 * wrong sizes.
1178 */
1179 if (S_ISREG(inode->i_mode)) {
1180 size = ui->xattr_size;
1181 size += stat->size;
1182 size = ALIGN(size, UBIFS_BLOCK_SIZE);
1183 /*
1184 * Note, user-space expects 512-byte blocks count irrespectively
1185 * of what was reported in @stat->size.
1186 */
1187 stat->blocks = size >> 9;
1188 } else
1189 stat->blocks = 0;
1190 mutex_unlock(&ui->ui_mutex);
1191 return 0;
1192 }
这个函数需要注意1168行开始的代码注释部分，ubifs不像传统的block filesystem，因此在汇报stat->blocks时有些问题，需要应用程序小心使用stat在ubifs文件系统的返回值