xref: /linux/fs/sysv/dir.c (revision 2363088eba2ecccfb643725e4864af73c4226a04)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  *  linux/fs/sysv/dir.c
4  *
5  *  minix/dir.c
6  *  Copyright (C) 1991, 1992  Linus Torvalds
7  *
8  *  coh/dir.c
9  *  Copyright (C) 1993  Pascal Haible, Bruno Haible
10  *
11  *  sysv/dir.c
12  *  Copyright (C) 1993  Bruno Haible
13  *
14  *  SystemV/Coherent directory handling functions
15  */
16 
17 #include <linux/pagemap.h>
18 #include <linux/highmem.h>
19 #include <linux/swap.h>
20 #include "sysv.h"
21 
22 static int sysv_readdir(struct file *, struct dir_context *);
23 
24 const struct file_operations sysv_dir_operations = {
25 	.llseek		= generic_file_llseek,
26 	.read		= generic_read_dir,
27 	.iterate_shared	= sysv_readdir,
28 	.fsync		= generic_file_fsync,
29 };
30 
31 static void dir_commit_chunk(struct page *page, loff_t pos, unsigned len)
32 {
33 	struct address_space *mapping = page->mapping;
34 	struct inode *dir = mapping->host;
35 
36 	block_write_end(NULL, mapping, pos, len, len, page, NULL);
37 	if (pos+len > dir->i_size) {
38 		i_size_write(dir, pos+len);
39 		mark_inode_dirty(dir);
40 	}
41 	unlock_page(page);
42 }
43 
44 static int sysv_handle_dirsync(struct inode *dir)
45 {
46 	int err;
47 
48 	err = filemap_write_and_wait(dir->i_mapping);
49 	if (!err)
50 		err = sync_inode_metadata(dir, 1);
51 	return err;
52 }
53 
54 /*
55  * Calls to dir_get_page()/unmap_and_put_page() must be nested according to the
56  * rules documented in mm/highmem.rst.
57  *
58  * NOTE: sysv_find_entry() and sysv_dotdot() act as calls to dir_get_page()
59  * and must be treated accordingly for nesting purposes.
60  */
61 static void *dir_get_page(struct inode *dir, unsigned long n, struct page **p)
62 {
63 	struct address_space *mapping = dir->i_mapping;
64 	struct page *page = read_mapping_page(mapping, n, NULL);
65 	if (IS_ERR(page))
66 		return ERR_CAST(page);
67 	*p = page;
68 	return kmap_local_page(page);
69 }
70 
71 static int sysv_readdir(struct file *file, struct dir_context *ctx)
72 {
73 	unsigned long pos = ctx->pos;
74 	struct inode *inode = file_inode(file);
75 	struct super_block *sb = inode->i_sb;
76 	unsigned long npages = dir_pages(inode);
77 	unsigned offset;
78 	unsigned long n;
79 
80 	ctx->pos = pos = (pos + SYSV_DIRSIZE-1) & ~(SYSV_DIRSIZE-1);
81 	if (pos >= inode->i_size)
82 		return 0;
83 
84 	offset = pos & ~PAGE_MASK;
85 	n = pos >> PAGE_SHIFT;
86 
87 	for ( ; n < npages; n++, offset = 0) {
88 		char *kaddr, *limit;
89 		struct sysv_dir_entry *de;
90 		struct page *page;
91 
92 		kaddr = dir_get_page(inode, n, &page);
93 		if (IS_ERR(kaddr))
94 			continue;
95 		de = (struct sysv_dir_entry *)(kaddr+offset);
96 		limit = kaddr + PAGE_SIZE - SYSV_DIRSIZE;
97 		for ( ;(char*)de <= limit; de++, ctx->pos += sizeof(*de)) {
98 			char *name = de->name;
99 
100 			if (!de->inode)
101 				continue;
102 
103 			if (!dir_emit(ctx, name, strnlen(name,SYSV_NAMELEN),
104 					fs16_to_cpu(SYSV_SB(sb), de->inode),
105 					DT_UNKNOWN)) {
106 				unmap_and_put_page(page, kaddr);
107 				return 0;
108 			}
109 		}
110 		unmap_and_put_page(page, kaddr);
111 	}
112 	return 0;
113 }
114 
115 /* compare strings: name[0..len-1] (not zero-terminated) and
116  * buffer[0..] (filled with zeroes up to buffer[0..maxlen-1])
117  */
118 static inline int namecompare(int len, int maxlen,
119 	const char * name, const char * buffer)
120 {
121 	if (len < maxlen && buffer[len])
122 		return 0;
123 	return !memcmp(name, buffer, len);
124 }
125 
126 /*
127  *	sysv_find_entry()
128  *
129  * finds an entry in the specified directory with the wanted name. It
130  * returns the cache buffer in which the entry was found, and the entry
131  * itself (as a parameter - res_dir). It does NOT read the inode of the
132  * entry - you'll have to do that yourself if you want to.
133  *
134  * On Success unmap_and_put_page() should be called on *res_page.
135  *
136  * sysv_find_entry() acts as a call to dir_get_page() and must be treated
137  * accordingly for nesting purposes.
138  */
139 struct sysv_dir_entry *sysv_find_entry(struct dentry *dentry, struct page **res_page)
140 {
141 	const char * name = dentry->d_name.name;
142 	int namelen = dentry->d_name.len;
143 	struct inode * dir = d_inode(dentry->d_parent);
144 	unsigned long start, n;
145 	unsigned long npages = dir_pages(dir);
146 	struct page *page = NULL;
147 	struct sysv_dir_entry *de;
148 
149 	*res_page = NULL;
150 
151 	start = SYSV_I(dir)->i_dir_start_lookup;
152 	if (start >= npages)
153 		start = 0;
154 	n = start;
155 
156 	do {
157 		char *kaddr = dir_get_page(dir, n, &page);
158 
159 		if (!IS_ERR(kaddr)) {
160 			de = (struct sysv_dir_entry *)kaddr;
161 			kaddr += PAGE_SIZE - SYSV_DIRSIZE;
162 			for ( ; (char *) de <= kaddr ; de++) {
163 				if (!de->inode)
164 					continue;
165 				if (namecompare(namelen, SYSV_NAMELEN,
166 							name, de->name))
167 					goto found;
168 			}
169 			unmap_and_put_page(page, kaddr);
170 		}
171 
172 		if (++n >= npages)
173 			n = 0;
174 	} while (n != start);
175 
176 	return NULL;
177 
178 found:
179 	SYSV_I(dir)->i_dir_start_lookup = n;
180 	*res_page = page;
181 	return de;
182 }
183 
184 int sysv_add_link(struct dentry *dentry, struct inode *inode)
185 {
186 	struct inode *dir = d_inode(dentry->d_parent);
187 	const char * name = dentry->d_name.name;
188 	int namelen = dentry->d_name.len;
189 	struct page *page = NULL;
190 	struct sysv_dir_entry * de;
191 	unsigned long npages = dir_pages(dir);
192 	unsigned long n;
193 	char *kaddr;
194 	loff_t pos;
195 	int err;
196 
197 	/* We take care of directory expansion in the same loop */
198 	for (n = 0; n <= npages; n++) {
199 		kaddr = dir_get_page(dir, n, &page);
200 		if (IS_ERR(kaddr))
201 			return PTR_ERR(kaddr);
202 		de = (struct sysv_dir_entry *)kaddr;
203 		kaddr += PAGE_SIZE - SYSV_DIRSIZE;
204 		while ((char *)de <= kaddr) {
205 			if (!de->inode)
206 				goto got_it;
207 			err = -EEXIST;
208 			if (namecompare(namelen, SYSV_NAMELEN, name, de->name))
209 				goto out_page;
210 			de++;
211 		}
212 		unmap_and_put_page(page, kaddr);
213 	}
214 	BUG();
215 	return -EINVAL;
216 
217 got_it:
218 	pos = page_offset(page) + offset_in_page(de);
219 	lock_page(page);
220 	err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
221 	if (err)
222 		goto out_unlock;
223 	memcpy (de->name, name, namelen);
224 	memset (de->name + namelen, 0, SYSV_DIRSIZE - namelen - 2);
225 	de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
226 	dir_commit_chunk(page, pos, SYSV_DIRSIZE);
227 	dir->i_mtime = dir->i_ctime = current_time(dir);
228 	mark_inode_dirty(dir);
229 	err = sysv_handle_dirsync(dir);
230 out_page:
231 	unmap_and_put_page(page, kaddr);
232 	return err;
233 out_unlock:
234 	unlock_page(page);
235 	goto out_page;
236 }
237 
238 int sysv_delete_entry(struct sysv_dir_entry *de, struct page *page)
239 {
240 	struct inode *inode = page->mapping->host;
241 	loff_t pos = page_offset(page) + offset_in_page(de);
242 	int err;
243 
244 	lock_page(page);
245 	err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
246 	if (err) {
247 		unlock_page(page);
248 		return err;
249 	}
250 	de->inode = 0;
251 	dir_commit_chunk(page, pos, SYSV_DIRSIZE);
252 	inode->i_ctime = inode->i_mtime = current_time(inode);
253 	mark_inode_dirty(inode);
254 	return sysv_handle_dirsync(inode);
255 }
256 
257 int sysv_make_empty(struct inode *inode, struct inode *dir)
258 {
259 	struct page *page = grab_cache_page(inode->i_mapping, 0);
260 	struct sysv_dir_entry * de;
261 	char *base;
262 	int err;
263 
264 	if (!page)
265 		return -ENOMEM;
266 	err = sysv_prepare_chunk(page, 0, 2 * SYSV_DIRSIZE);
267 	if (err) {
268 		unlock_page(page);
269 		goto fail;
270 	}
271 	base = kmap_local_page(page);
272 	memset(base, 0, PAGE_SIZE);
273 
274 	de = (struct sysv_dir_entry *) base;
275 	de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
276 	strcpy(de->name,".");
277 	de++;
278 	de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), dir->i_ino);
279 	strcpy(de->name,"..");
280 
281 	kunmap_local(base);
282 	dir_commit_chunk(page, 0, 2 * SYSV_DIRSIZE);
283 	err = sysv_handle_dirsync(inode);
284 fail:
285 	put_page(page);
286 	return err;
287 }
288 
289 /*
290  * routine to check that the specified directory is empty (for rmdir)
291  */
292 int sysv_empty_dir(struct inode * inode)
293 {
294 	struct super_block *sb = inode->i_sb;
295 	struct page *page = NULL;
296 	unsigned long i, npages = dir_pages(inode);
297 	char *kaddr;
298 
299 	for (i = 0; i < npages; i++) {
300 		struct sysv_dir_entry *de;
301 
302 		kaddr = dir_get_page(inode, i, &page);
303 		if (IS_ERR(kaddr))
304 			continue;
305 
306 		de = (struct sysv_dir_entry *)kaddr;
307 		kaddr += PAGE_SIZE-SYSV_DIRSIZE;
308 
309 		for ( ;(char *)de <= kaddr; de++) {
310 			if (!de->inode)
311 				continue;
312 			/* check for . and .. */
313 			if (de->name[0] != '.')
314 				goto not_empty;
315 			if (!de->name[1]) {
316 				if (de->inode == cpu_to_fs16(SYSV_SB(sb),
317 							inode->i_ino))
318 					continue;
319 				goto not_empty;
320 			}
321 			if (de->name[1] != '.' || de->name[2])
322 				goto not_empty;
323 		}
324 		unmap_and_put_page(page, kaddr);
325 	}
326 	return 1;
327 
328 not_empty:
329 	unmap_and_put_page(page, kaddr);
330 	return 0;
331 }
332 
333 /* Releases the page */
334 int sysv_set_link(struct sysv_dir_entry *de, struct page *page,
335 	struct inode *inode)
336 {
337 	struct inode *dir = page->mapping->host;
338 	loff_t pos = page_offset(page) + offset_in_page(de);
339 	int err;
340 
341 	lock_page(page);
342 	err = sysv_prepare_chunk(page, pos, SYSV_DIRSIZE);
343 	if (err) {
344 		unlock_page(page);
345 		return err;
346 	}
347 	de->inode = cpu_to_fs16(SYSV_SB(inode->i_sb), inode->i_ino);
348 	dir_commit_chunk(page, pos, SYSV_DIRSIZE);
349 	dir->i_mtime = dir->i_ctime = current_time(dir);
350 	mark_inode_dirty(dir);
351 	return sysv_handle_dirsync(inode);
352 }
353 
354 /*
355  * Calls to dir_get_page()/unmap_and_put_page() must be nested according to the
356  * rules documented in mm/highmem.rst.
357  *
358  * sysv_dotdot() acts as a call to dir_get_page() and must be treated
359  * accordingly for nesting purposes.
360  */
361 struct sysv_dir_entry *sysv_dotdot(struct inode *dir, struct page **p)
362 {
363 	struct sysv_dir_entry *de = dir_get_page(dir, 0, p);
364 
365 	if (IS_ERR(de))
366 		return NULL;
367 	/* ".." is the second directory entry */
368 	return de + 1;
369 }
370 
371 ino_t sysv_inode_by_name(struct dentry *dentry)
372 {
373 	struct page *page;
374 	struct sysv_dir_entry *de = sysv_find_entry (dentry, &page);
375 	ino_t res = 0;
376 
377 	if (de) {
378 		res = fs16_to_cpu(SYSV_SB(dentry->d_sb), de->inode);
379 		unmap_and_put_page(page, de);
380 	}
381 	return res;
382 }
383