xref: /openbmc/linux/mm/shmem.c (revision b6dcefde)
1 /*
2  * Resizable virtual memory filesystem for Linux.
3  *
4  * Copyright (C) 2000 Linus Torvalds.
5  *		 2000 Transmeta Corp.
6  *		 2000-2001 Christoph Rohland
7  *		 2000-2001 SAP AG
8  *		 2002 Red Hat Inc.
9  * Copyright (C) 2002-2005 Hugh Dickins.
10  * Copyright (C) 2002-2005 VERITAS Software Corporation.
11  * Copyright (C) 2004 Andi Kleen, SuSE Labs
12  *
13  * Extended attribute support for tmpfs:
14  * Copyright (c) 2004, Luke Kenneth Casson Leighton <lkcl@lkcl.net>
15  * Copyright (c) 2004 Red Hat, Inc., James Morris <jmorris@redhat.com>
16  *
17  * tiny-shmem:
18  * Copyright (c) 2004, 2008 Matt Mackall <mpm@selenic.com>
19  *
20  * This file is released under the GPL.
21  */
22 
23 #include <linux/fs.h>
24 #include <linux/init.h>
25 #include <linux/vfs.h>
26 #include <linux/mount.h>
27 #include <linux/pagemap.h>
28 #include <linux/file.h>
29 #include <linux/mm.h>
30 #include <linux/module.h>
31 #include <linux/swap.h>
32 
33 static struct vfsmount *shm_mnt;
34 
35 #ifdef CONFIG_SHMEM
36 /*
37  * This virtual memory filesystem is heavily based on the ramfs. It
38  * extends ramfs by the ability to use swap and honor resource limits
39  * which makes it a completely usable filesystem.
40  */
41 
42 #include <linux/xattr.h>
43 #include <linux/exportfs.h>
44 #include <linux/posix_acl.h>
45 #include <linux/generic_acl.h>
46 #include <linux/mman.h>
47 #include <linux/string.h>
48 #include <linux/slab.h>
49 #include <linux/backing-dev.h>
50 #include <linux/shmem_fs.h>
51 #include <linux/writeback.h>
52 #include <linux/blkdev.h>
53 #include <linux/security.h>
54 #include <linux/swapops.h>
55 #include <linux/mempolicy.h>
56 #include <linux/namei.h>
57 #include <linux/ctype.h>
58 #include <linux/migrate.h>
59 #include <linux/highmem.h>
60 #include <linux/seq_file.h>
61 #include <linux/magic.h>
62 
63 #include <asm/uaccess.h>
64 #include <asm/div64.h>
65 #include <asm/pgtable.h>
66 
67 /*
68  * The maximum size of a shmem/tmpfs file is limited by the maximum size of
69  * its triple-indirect swap vector - see illustration at shmem_swp_entry().
70  *
71  * With 4kB page size, maximum file size is just over 2TB on a 32-bit kernel,
72  * but one eighth of that on a 64-bit kernel.  With 8kB page size, maximum
73  * file size is just over 4TB on a 64-bit kernel, but 16TB on a 32-bit kernel,
74  * MAX_LFS_FILESIZE being then more restrictive than swap vector layout.
75  *
76  * We use / and * instead of shifts in the definitions below, so that the swap
77  * vector can be tested with small even values (e.g. 20) for ENTRIES_PER_PAGE.
78  */
79 #define ENTRIES_PER_PAGE (PAGE_CACHE_SIZE/sizeof(unsigned long))
80 #define ENTRIES_PER_PAGEPAGE ((unsigned long long)ENTRIES_PER_PAGE*ENTRIES_PER_PAGE)
81 
82 #define SHMSWP_MAX_INDEX (SHMEM_NR_DIRECT + (ENTRIES_PER_PAGEPAGE/2) * (ENTRIES_PER_PAGE+1))
83 #define SHMSWP_MAX_BYTES (SHMSWP_MAX_INDEX << PAGE_CACHE_SHIFT)
84 
85 #define SHMEM_MAX_BYTES  min_t(unsigned long long, SHMSWP_MAX_BYTES, MAX_LFS_FILESIZE)
86 #define SHMEM_MAX_INDEX  ((unsigned long)((SHMEM_MAX_BYTES+1) >> PAGE_CACHE_SHIFT))
87 
88 #define BLOCKS_PER_PAGE  (PAGE_CACHE_SIZE/512)
89 #define VM_ACCT(size)    (PAGE_CACHE_ALIGN(size) >> PAGE_SHIFT)
90 
91 /* info->flags needs VM_flags to handle pagein/truncate races efficiently */
92 #define SHMEM_PAGEIN	 VM_READ
93 #define SHMEM_TRUNCATE	 VM_WRITE
94 
95 /* Definition to limit shmem_truncate's steps between cond_rescheds */
96 #define LATENCY_LIMIT	 64
97 
98 /* Pretend that each entry is of this size in directory's i_size */
99 #define BOGO_DIRENT_SIZE 20
100 
101 /* Flag allocation requirements to shmem_getpage and shmem_swp_alloc */
102 enum sgp_type {
103 	SGP_READ,	/* don't exceed i_size, don't allocate page */
104 	SGP_CACHE,	/* don't exceed i_size, may allocate page */
105 	SGP_DIRTY,	/* like SGP_CACHE, but set new page dirty */
106 	SGP_WRITE,	/* may exceed i_size, may allocate page */
107 };
108 
109 #ifdef CONFIG_TMPFS
110 static unsigned long shmem_default_max_blocks(void)
111 {
112 	return totalram_pages / 2;
113 }
114 
115 static unsigned long shmem_default_max_inodes(void)
116 {
117 	return min(totalram_pages - totalhigh_pages, totalram_pages / 2);
118 }
119 #endif
120 
121 static int shmem_getpage(struct inode *inode, unsigned long idx,
122 			 struct page **pagep, enum sgp_type sgp, int *type);
123 
124 static inline struct page *shmem_dir_alloc(gfp_t gfp_mask)
125 {
126 	/*
127 	 * The above definition of ENTRIES_PER_PAGE, and the use of
128 	 * BLOCKS_PER_PAGE on indirect pages, assume PAGE_CACHE_SIZE:
129 	 * might be reconsidered if it ever diverges from PAGE_SIZE.
130 	 *
131 	 * Mobility flags are masked out as swap vectors cannot move
132 	 */
133 	return alloc_pages((gfp_mask & ~GFP_MOVABLE_MASK) | __GFP_ZERO,
134 				PAGE_CACHE_SHIFT-PAGE_SHIFT);
135 }
136 
137 static inline void shmem_dir_free(struct page *page)
138 {
139 	__free_pages(page, PAGE_CACHE_SHIFT-PAGE_SHIFT);
140 }
141 
142 static struct page **shmem_dir_map(struct page *page)
143 {
144 	return (struct page **)kmap_atomic(page, KM_USER0);
145 }
146 
147 static inline void shmem_dir_unmap(struct page **dir)
148 {
149 	kunmap_atomic(dir, KM_USER0);
150 }
151 
152 static swp_entry_t *shmem_swp_map(struct page *page)
153 {
154 	return (swp_entry_t *)kmap_atomic(page, KM_USER1);
155 }
156 
157 static inline void shmem_swp_balance_unmap(void)
158 {
159 	/*
160 	 * When passing a pointer to an i_direct entry, to code which
161 	 * also handles indirect entries and so will shmem_swp_unmap,
162 	 * we must arrange for the preempt count to remain in balance.
163 	 * What kmap_atomic of a lowmem page does depends on config
164 	 * and architecture, so pretend to kmap_atomic some lowmem page.
165 	 */
166 	(void) kmap_atomic(ZERO_PAGE(0), KM_USER1);
167 }
168 
169 static inline void shmem_swp_unmap(swp_entry_t *entry)
170 {
171 	kunmap_atomic(entry, KM_USER1);
172 }
173 
174 static inline struct shmem_sb_info *SHMEM_SB(struct super_block *sb)
175 {
176 	return sb->s_fs_info;
177 }
178 
179 /*
180  * shmem_file_setup pre-accounts the whole fixed size of a VM object,
181  * for shared memory and for shared anonymous (/dev/zero) mappings
182  * (unless MAP_NORESERVE and sysctl_overcommit_memory <= 1),
183  * consistent with the pre-accounting of private mappings ...
184  */
185 static inline int shmem_acct_size(unsigned long flags, loff_t size)
186 {
187 	return (flags & VM_NORESERVE) ?
188 		0 : security_vm_enough_memory_kern(VM_ACCT(size));
189 }
190 
191 static inline void shmem_unacct_size(unsigned long flags, loff_t size)
192 {
193 	if (!(flags & VM_NORESERVE))
194 		vm_unacct_memory(VM_ACCT(size));
195 }
196 
197 /*
198  * ... whereas tmpfs objects are accounted incrementally as
199  * pages are allocated, in order to allow huge sparse files.
200  * shmem_getpage reports shmem_acct_block failure as -ENOSPC not -ENOMEM,
201  * so that a failure on a sparse tmpfs mapping will give SIGBUS not OOM.
202  */
203 static inline int shmem_acct_block(unsigned long flags)
204 {
205 	return (flags & VM_NORESERVE) ?
206 		security_vm_enough_memory_kern(VM_ACCT(PAGE_CACHE_SIZE)) : 0;
207 }
208 
209 static inline void shmem_unacct_blocks(unsigned long flags, long pages)
210 {
211 	if (flags & VM_NORESERVE)
212 		vm_unacct_memory(pages * VM_ACCT(PAGE_CACHE_SIZE));
213 }
214 
215 static const struct super_operations shmem_ops;
216 static const struct address_space_operations shmem_aops;
217 static const struct file_operations shmem_file_operations;
218 static const struct inode_operations shmem_inode_operations;
219 static const struct inode_operations shmem_dir_inode_operations;
220 static const struct inode_operations shmem_special_inode_operations;
221 static const struct vm_operations_struct shmem_vm_ops;
222 
223 static struct backing_dev_info shmem_backing_dev_info  __read_mostly = {
224 	.ra_pages	= 0,	/* No readahead */
225 	.capabilities	= BDI_CAP_NO_ACCT_AND_WRITEBACK | BDI_CAP_SWAP_BACKED,
226 	.unplug_io_fn	= default_unplug_io_fn,
227 };
228 
229 static LIST_HEAD(shmem_swaplist);
230 static DEFINE_MUTEX(shmem_swaplist_mutex);
231 
232 static void shmem_free_blocks(struct inode *inode, long pages)
233 {
234 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
235 	if (sbinfo->max_blocks) {
236 		spin_lock(&sbinfo->stat_lock);
237 		sbinfo->free_blocks += pages;
238 		inode->i_blocks -= pages*BLOCKS_PER_PAGE;
239 		spin_unlock(&sbinfo->stat_lock);
240 	}
241 }
242 
243 static int shmem_reserve_inode(struct super_block *sb)
244 {
245 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
246 	if (sbinfo->max_inodes) {
247 		spin_lock(&sbinfo->stat_lock);
248 		if (!sbinfo->free_inodes) {
249 			spin_unlock(&sbinfo->stat_lock);
250 			return -ENOSPC;
251 		}
252 		sbinfo->free_inodes--;
253 		spin_unlock(&sbinfo->stat_lock);
254 	}
255 	return 0;
256 }
257 
258 static void shmem_free_inode(struct super_block *sb)
259 {
260 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
261 	if (sbinfo->max_inodes) {
262 		spin_lock(&sbinfo->stat_lock);
263 		sbinfo->free_inodes++;
264 		spin_unlock(&sbinfo->stat_lock);
265 	}
266 }
267 
268 /**
269  * shmem_recalc_inode - recalculate the size of an inode
270  * @inode: inode to recalc
271  *
272  * We have to calculate the free blocks since the mm can drop
273  * undirtied hole pages behind our back.
274  *
275  * But normally   info->alloced == inode->i_mapping->nrpages + info->swapped
276  * So mm freed is info->alloced - (inode->i_mapping->nrpages + info->swapped)
277  *
278  * It has to be called with the spinlock held.
279  */
280 static void shmem_recalc_inode(struct inode *inode)
281 {
282 	struct shmem_inode_info *info = SHMEM_I(inode);
283 	long freed;
284 
285 	freed = info->alloced - info->swapped - inode->i_mapping->nrpages;
286 	if (freed > 0) {
287 		info->alloced -= freed;
288 		shmem_unacct_blocks(info->flags, freed);
289 		shmem_free_blocks(inode, freed);
290 	}
291 }
292 
293 /**
294  * shmem_swp_entry - find the swap vector position in the info structure
295  * @info:  info structure for the inode
296  * @index: index of the page to find
297  * @page:  optional page to add to the structure. Has to be preset to
298  *         all zeros
299  *
300  * If there is no space allocated yet it will return NULL when
301  * page is NULL, else it will use the page for the needed block,
302  * setting it to NULL on return to indicate that it has been used.
303  *
304  * The swap vector is organized the following way:
305  *
306  * There are SHMEM_NR_DIRECT entries directly stored in the
307  * shmem_inode_info structure. So small files do not need an addional
308  * allocation.
309  *
310  * For pages with index > SHMEM_NR_DIRECT there is the pointer
311  * i_indirect which points to a page which holds in the first half
312  * doubly indirect blocks, in the second half triple indirect blocks:
313  *
314  * For an artificial ENTRIES_PER_PAGE = 4 this would lead to the
315  * following layout (for SHMEM_NR_DIRECT == 16):
316  *
317  * i_indirect -> dir --> 16-19
318  * 	      |	     +-> 20-23
319  * 	      |
320  * 	      +-->dir2 --> 24-27
321  * 	      |	       +-> 28-31
322  * 	      |	       +-> 32-35
323  * 	      |	       +-> 36-39
324  * 	      |
325  * 	      +-->dir3 --> 40-43
326  * 	       	       +-> 44-47
327  * 	      	       +-> 48-51
328  * 	      	       +-> 52-55
329  */
330 static swp_entry_t *shmem_swp_entry(struct shmem_inode_info *info, unsigned long index, struct page **page)
331 {
332 	unsigned long offset;
333 	struct page **dir;
334 	struct page *subdir;
335 
336 	if (index < SHMEM_NR_DIRECT) {
337 		shmem_swp_balance_unmap();
338 		return info->i_direct+index;
339 	}
340 	if (!info->i_indirect) {
341 		if (page) {
342 			info->i_indirect = *page;
343 			*page = NULL;
344 		}
345 		return NULL;			/* need another page */
346 	}
347 
348 	index -= SHMEM_NR_DIRECT;
349 	offset = index % ENTRIES_PER_PAGE;
350 	index /= ENTRIES_PER_PAGE;
351 	dir = shmem_dir_map(info->i_indirect);
352 
353 	if (index >= ENTRIES_PER_PAGE/2) {
354 		index -= ENTRIES_PER_PAGE/2;
355 		dir += ENTRIES_PER_PAGE/2 + index/ENTRIES_PER_PAGE;
356 		index %= ENTRIES_PER_PAGE;
357 		subdir = *dir;
358 		if (!subdir) {
359 			if (page) {
360 				*dir = *page;
361 				*page = NULL;
362 			}
363 			shmem_dir_unmap(dir);
364 			return NULL;		/* need another page */
365 		}
366 		shmem_dir_unmap(dir);
367 		dir = shmem_dir_map(subdir);
368 	}
369 
370 	dir += index;
371 	subdir = *dir;
372 	if (!subdir) {
373 		if (!page || !(subdir = *page)) {
374 			shmem_dir_unmap(dir);
375 			return NULL;		/* need a page */
376 		}
377 		*dir = subdir;
378 		*page = NULL;
379 	}
380 	shmem_dir_unmap(dir);
381 	return shmem_swp_map(subdir) + offset;
382 }
383 
384 static void shmem_swp_set(struct shmem_inode_info *info, swp_entry_t *entry, unsigned long value)
385 {
386 	long incdec = value? 1: -1;
387 
388 	entry->val = value;
389 	info->swapped += incdec;
390 	if ((unsigned long)(entry - info->i_direct) >= SHMEM_NR_DIRECT) {
391 		struct page *page = kmap_atomic_to_page(entry);
392 		set_page_private(page, page_private(page) + incdec);
393 	}
394 }
395 
396 /**
397  * shmem_swp_alloc - get the position of the swap entry for the page.
398  * @info:	info structure for the inode
399  * @index:	index of the page to find
400  * @sgp:	check and recheck i_size? skip allocation?
401  *
402  * If the entry does not exist, allocate it.
403  */
404 static swp_entry_t *shmem_swp_alloc(struct shmem_inode_info *info, unsigned long index, enum sgp_type sgp)
405 {
406 	struct inode *inode = &info->vfs_inode;
407 	struct shmem_sb_info *sbinfo = SHMEM_SB(inode->i_sb);
408 	struct page *page = NULL;
409 	swp_entry_t *entry;
410 
411 	if (sgp != SGP_WRITE &&
412 	    ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode))
413 		return ERR_PTR(-EINVAL);
414 
415 	while (!(entry = shmem_swp_entry(info, index, &page))) {
416 		if (sgp == SGP_READ)
417 			return shmem_swp_map(ZERO_PAGE(0));
418 		/*
419 		 * Test free_blocks against 1 not 0, since we have 1 data
420 		 * page (and perhaps indirect index pages) yet to allocate:
421 		 * a waste to allocate index if we cannot allocate data.
422 		 */
423 		if (sbinfo->max_blocks) {
424 			spin_lock(&sbinfo->stat_lock);
425 			if (sbinfo->free_blocks <= 1) {
426 				spin_unlock(&sbinfo->stat_lock);
427 				return ERR_PTR(-ENOSPC);
428 			}
429 			sbinfo->free_blocks--;
430 			inode->i_blocks += BLOCKS_PER_PAGE;
431 			spin_unlock(&sbinfo->stat_lock);
432 		}
433 
434 		spin_unlock(&info->lock);
435 		page = shmem_dir_alloc(mapping_gfp_mask(inode->i_mapping));
436 		if (page)
437 			set_page_private(page, 0);
438 		spin_lock(&info->lock);
439 
440 		if (!page) {
441 			shmem_free_blocks(inode, 1);
442 			return ERR_PTR(-ENOMEM);
443 		}
444 		if (sgp != SGP_WRITE &&
445 		    ((loff_t) index << PAGE_CACHE_SHIFT) >= i_size_read(inode)) {
446 			entry = ERR_PTR(-EINVAL);
447 			break;
448 		}
449 		if (info->next_index <= index)
450 			info->next_index = index + 1;
451 	}
452 	if (page) {
453 		/* another task gave its page, or truncated the file */
454 		shmem_free_blocks(inode, 1);
455 		shmem_dir_free(page);
456 	}
457 	if (info->next_index <= index && !IS_ERR(entry))
458 		info->next_index = index + 1;
459 	return entry;
460 }
461 
462 /**
463  * shmem_free_swp - free some swap entries in a directory
464  * @dir:        pointer to the directory
465  * @edir:       pointer after last entry of the directory
466  * @punch_lock: pointer to spinlock when needed for the holepunch case
467  */
468 static int shmem_free_swp(swp_entry_t *dir, swp_entry_t *edir,
469 						spinlock_t *punch_lock)
470 {
471 	spinlock_t *punch_unlock = NULL;
472 	swp_entry_t *ptr;
473 	int freed = 0;
474 
475 	for (ptr = dir; ptr < edir; ptr++) {
476 		if (ptr->val) {
477 			if (unlikely(punch_lock)) {
478 				punch_unlock = punch_lock;
479 				punch_lock = NULL;
480 				spin_lock(punch_unlock);
481 				if (!ptr->val)
482 					continue;
483 			}
484 			free_swap_and_cache(*ptr);
485 			*ptr = (swp_entry_t){0};
486 			freed++;
487 		}
488 	}
489 	if (punch_unlock)
490 		spin_unlock(punch_unlock);
491 	return freed;
492 }
493 
494 static int shmem_map_and_free_swp(struct page *subdir, int offset,
495 		int limit, struct page ***dir, spinlock_t *punch_lock)
496 {
497 	swp_entry_t *ptr;
498 	int freed = 0;
499 
500 	ptr = shmem_swp_map(subdir);
501 	for (; offset < limit; offset += LATENCY_LIMIT) {
502 		int size = limit - offset;
503 		if (size > LATENCY_LIMIT)
504 			size = LATENCY_LIMIT;
505 		freed += shmem_free_swp(ptr+offset, ptr+offset+size,
506 							punch_lock);
507 		if (need_resched()) {
508 			shmem_swp_unmap(ptr);
509 			if (*dir) {
510 				shmem_dir_unmap(*dir);
511 				*dir = NULL;
512 			}
513 			cond_resched();
514 			ptr = shmem_swp_map(subdir);
515 		}
516 	}
517 	shmem_swp_unmap(ptr);
518 	return freed;
519 }
520 
521 static void shmem_free_pages(struct list_head *next)
522 {
523 	struct page *page;
524 	int freed = 0;
525 
526 	do {
527 		page = container_of(next, struct page, lru);
528 		next = next->next;
529 		shmem_dir_free(page);
530 		freed++;
531 		if (freed >= LATENCY_LIMIT) {
532 			cond_resched();
533 			freed = 0;
534 		}
535 	} while (next);
536 }
537 
538 static void shmem_truncate_range(struct inode *inode, loff_t start, loff_t end)
539 {
540 	struct shmem_inode_info *info = SHMEM_I(inode);
541 	unsigned long idx;
542 	unsigned long size;
543 	unsigned long limit;
544 	unsigned long stage;
545 	unsigned long diroff;
546 	struct page **dir;
547 	struct page *topdir;
548 	struct page *middir;
549 	struct page *subdir;
550 	swp_entry_t *ptr;
551 	LIST_HEAD(pages_to_free);
552 	long nr_pages_to_free = 0;
553 	long nr_swaps_freed = 0;
554 	int offset;
555 	int freed;
556 	int punch_hole;
557 	spinlock_t *needs_lock;
558 	spinlock_t *punch_lock;
559 	unsigned long upper_limit;
560 
561 	inode->i_ctime = inode->i_mtime = CURRENT_TIME;
562 	idx = (start + PAGE_CACHE_SIZE - 1) >> PAGE_CACHE_SHIFT;
563 	if (idx >= info->next_index)
564 		return;
565 
566 	spin_lock(&info->lock);
567 	info->flags |= SHMEM_TRUNCATE;
568 	if (likely(end == (loff_t) -1)) {
569 		limit = info->next_index;
570 		upper_limit = SHMEM_MAX_INDEX;
571 		info->next_index = idx;
572 		needs_lock = NULL;
573 		punch_hole = 0;
574 	} else {
575 		if (end + 1 >= inode->i_size) {	/* we may free a little more */
576 			limit = (inode->i_size + PAGE_CACHE_SIZE - 1) >>
577 							PAGE_CACHE_SHIFT;
578 			upper_limit = SHMEM_MAX_INDEX;
579 		} else {
580 			limit = (end + 1) >> PAGE_CACHE_SHIFT;
581 			upper_limit = limit;
582 		}
583 		needs_lock = &info->lock;
584 		punch_hole = 1;
585 	}
586 
587 	topdir = info->i_indirect;
588 	if (topdir && idx <= SHMEM_NR_DIRECT && !punch_hole) {
589 		info->i_indirect = NULL;
590 		nr_pages_to_free++;
591 		list_add(&topdir->lru, &pages_to_free);
592 	}
593 	spin_unlock(&info->lock);
594 
595 	if (info->swapped && idx < SHMEM_NR_DIRECT) {
596 		ptr = info->i_direct;
597 		size = limit;
598 		if (size > SHMEM_NR_DIRECT)
599 			size = SHMEM_NR_DIRECT;
600 		nr_swaps_freed = shmem_free_swp(ptr+idx, ptr+size, needs_lock);
601 	}
602 
603 	/*
604 	 * If there are no indirect blocks or we are punching a hole
605 	 * below indirect blocks, nothing to be done.
606 	 */
607 	if (!topdir || limit <= SHMEM_NR_DIRECT)
608 		goto done2;
609 
610 	/*
611 	 * The truncation case has already dropped info->lock, and we're safe
612 	 * because i_size and next_index have already been lowered, preventing
613 	 * access beyond.  But in the punch_hole case, we still need to take
614 	 * the lock when updating the swap directory, because there might be
615 	 * racing accesses by shmem_getpage(SGP_CACHE), shmem_unuse_inode or
616 	 * shmem_writepage.  However, whenever we find we can remove a whole
617 	 * directory page (not at the misaligned start or end of the range),
618 	 * we first NULLify its pointer in the level above, and then have no
619 	 * need to take the lock when updating its contents: needs_lock and
620 	 * punch_lock (either pointing to info->lock or NULL) manage this.
621 	 */
622 
623 	upper_limit -= SHMEM_NR_DIRECT;
624 	limit -= SHMEM_NR_DIRECT;
625 	idx = (idx > SHMEM_NR_DIRECT)? (idx - SHMEM_NR_DIRECT): 0;
626 	offset = idx % ENTRIES_PER_PAGE;
627 	idx -= offset;
628 
629 	dir = shmem_dir_map(topdir);
630 	stage = ENTRIES_PER_PAGEPAGE/2;
631 	if (idx < ENTRIES_PER_PAGEPAGE/2) {
632 		middir = topdir;
633 		diroff = idx/ENTRIES_PER_PAGE;
634 	} else {
635 		dir += ENTRIES_PER_PAGE/2;
636 		dir += (idx - ENTRIES_PER_PAGEPAGE/2)/ENTRIES_PER_PAGEPAGE;
637 		while (stage <= idx)
638 			stage += ENTRIES_PER_PAGEPAGE;
639 		middir = *dir;
640 		if (*dir) {
641 			diroff = ((idx - ENTRIES_PER_PAGEPAGE/2) %
642 				ENTRIES_PER_PAGEPAGE) / ENTRIES_PER_PAGE;
643 			if (!diroff && !offset && upper_limit >= stage) {
644 				if (needs_lock) {
645 					spin_lock(needs_lock);
646 					*dir = NULL;
647 					spin_unlock(needs_lock);
648 					needs_lock = NULL;
649 				} else
650 					*dir = NULL;
651 				nr_pages_to_free++;
652 				list_add(&middir->lru, &pages_to_free);
653 			}
654 			shmem_dir_unmap(dir);
655 			dir = shmem_dir_map(middir);
656 		} else {
657 			diroff = 0;
658 			offset = 0;
659 			idx = stage;
660 		}
661 	}
662 
663 	for (; idx < limit; idx += ENTRIES_PER_PAGE, diroff++) {
664 		if (unlikely(idx == stage)) {
665 			shmem_dir_unmap(dir);
666 			dir = shmem_dir_map(topdir) +
667 			    ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
668 			while (!*dir) {
669 				dir++;
670 				idx += ENTRIES_PER_PAGEPAGE;
671 				if (idx >= limit)
672 					goto done1;
673 			}
674 			stage = idx + ENTRIES_PER_PAGEPAGE;
675 			middir = *dir;
676 			if (punch_hole)
677 				needs_lock = &info->lock;
678 			if (upper_limit >= stage) {
679 				if (needs_lock) {
680 					spin_lock(needs_lock);
681 					*dir = NULL;
682 					spin_unlock(needs_lock);
683 					needs_lock = NULL;
684 				} else
685 					*dir = NULL;
686 				nr_pages_to_free++;
687 				list_add(&middir->lru, &pages_to_free);
688 			}
689 			shmem_dir_unmap(dir);
690 			cond_resched();
691 			dir = shmem_dir_map(middir);
692 			diroff = 0;
693 		}
694 		punch_lock = needs_lock;
695 		subdir = dir[diroff];
696 		if (subdir && !offset && upper_limit-idx >= ENTRIES_PER_PAGE) {
697 			if (needs_lock) {
698 				spin_lock(needs_lock);
699 				dir[diroff] = NULL;
700 				spin_unlock(needs_lock);
701 				punch_lock = NULL;
702 			} else
703 				dir[diroff] = NULL;
704 			nr_pages_to_free++;
705 			list_add(&subdir->lru, &pages_to_free);
706 		}
707 		if (subdir && page_private(subdir) /* has swap entries */) {
708 			size = limit - idx;
709 			if (size > ENTRIES_PER_PAGE)
710 				size = ENTRIES_PER_PAGE;
711 			freed = shmem_map_and_free_swp(subdir,
712 					offset, size, &dir, punch_lock);
713 			if (!dir)
714 				dir = shmem_dir_map(middir);
715 			nr_swaps_freed += freed;
716 			if (offset || punch_lock) {
717 				spin_lock(&info->lock);
718 				set_page_private(subdir,
719 					page_private(subdir) - freed);
720 				spin_unlock(&info->lock);
721 			} else
722 				BUG_ON(page_private(subdir) != freed);
723 		}
724 		offset = 0;
725 	}
726 done1:
727 	shmem_dir_unmap(dir);
728 done2:
729 	if (inode->i_mapping->nrpages && (info->flags & SHMEM_PAGEIN)) {
730 		/*
731 		 * Call truncate_inode_pages again: racing shmem_unuse_inode
732 		 * may have swizzled a page in from swap since vmtruncate or
733 		 * generic_delete_inode did it, before we lowered next_index.
734 		 * Also, though shmem_getpage checks i_size before adding to
735 		 * cache, no recheck after: so fix the narrow window there too.
736 		 *
737 		 * Recalling truncate_inode_pages_range and unmap_mapping_range
738 		 * every time for punch_hole (which never got a chance to clear
739 		 * SHMEM_PAGEIN at the start of vmtruncate_range) is expensive,
740 		 * yet hardly ever necessary: try to optimize them out later.
741 		 */
742 		truncate_inode_pages_range(inode->i_mapping, start, end);
743 		if (punch_hole)
744 			unmap_mapping_range(inode->i_mapping, start,
745 							end - start, 1);
746 	}
747 
748 	spin_lock(&info->lock);
749 	info->flags &= ~SHMEM_TRUNCATE;
750 	info->swapped -= nr_swaps_freed;
751 	if (nr_pages_to_free)
752 		shmem_free_blocks(inode, nr_pages_to_free);
753 	shmem_recalc_inode(inode);
754 	spin_unlock(&info->lock);
755 
756 	/*
757 	 * Empty swap vector directory pages to be freed?
758 	 */
759 	if (!list_empty(&pages_to_free)) {
760 		pages_to_free.prev->next = NULL;
761 		shmem_free_pages(pages_to_free.next);
762 	}
763 }
764 
765 static void shmem_truncate(struct inode *inode)
766 {
767 	shmem_truncate_range(inode, inode->i_size, (loff_t)-1);
768 }
769 
770 static int shmem_notify_change(struct dentry *dentry, struct iattr *attr)
771 {
772 	struct inode *inode = dentry->d_inode;
773 	struct page *page = NULL;
774 	int error;
775 
776 	if (S_ISREG(inode->i_mode) && (attr->ia_valid & ATTR_SIZE)) {
777 		if (attr->ia_size < inode->i_size) {
778 			/*
779 			 * If truncating down to a partial page, then
780 			 * if that page is already allocated, hold it
781 			 * in memory until the truncation is over, so
782 			 * truncate_partial_page cannnot miss it were
783 			 * it assigned to swap.
784 			 */
785 			if (attr->ia_size & (PAGE_CACHE_SIZE-1)) {
786 				(void) shmem_getpage(inode,
787 					attr->ia_size>>PAGE_CACHE_SHIFT,
788 						&page, SGP_READ, NULL);
789 				if (page)
790 					unlock_page(page);
791 			}
792 			/*
793 			 * Reset SHMEM_PAGEIN flag so that shmem_truncate can
794 			 * detect if any pages might have been added to cache
795 			 * after truncate_inode_pages.  But we needn't bother
796 			 * if it's being fully truncated to zero-length: the
797 			 * nrpages check is efficient enough in that case.
798 			 */
799 			if (attr->ia_size) {
800 				struct shmem_inode_info *info = SHMEM_I(inode);
801 				spin_lock(&info->lock);
802 				info->flags &= ~SHMEM_PAGEIN;
803 				spin_unlock(&info->lock);
804 			}
805 		}
806 	}
807 
808 	error = inode_change_ok(inode, attr);
809 	if (!error)
810 		error = inode_setattr(inode, attr);
811 #ifdef CONFIG_TMPFS_POSIX_ACL
812 	if (!error && (attr->ia_valid & ATTR_MODE))
813 		error = generic_acl_chmod(inode);
814 #endif
815 	if (page)
816 		page_cache_release(page);
817 	return error;
818 }
819 
820 static void shmem_delete_inode(struct inode *inode)
821 {
822 	struct shmem_inode_info *info = SHMEM_I(inode);
823 
824 	if (inode->i_op->truncate == shmem_truncate) {
825 		truncate_inode_pages(inode->i_mapping, 0);
826 		shmem_unacct_size(info->flags, inode->i_size);
827 		inode->i_size = 0;
828 		shmem_truncate(inode);
829 		if (!list_empty(&info->swaplist)) {
830 			mutex_lock(&shmem_swaplist_mutex);
831 			list_del_init(&info->swaplist);
832 			mutex_unlock(&shmem_swaplist_mutex);
833 		}
834 	}
835 	BUG_ON(inode->i_blocks);
836 	shmem_free_inode(inode->i_sb);
837 	clear_inode(inode);
838 }
839 
840 static inline int shmem_find_swp(swp_entry_t entry, swp_entry_t *dir, swp_entry_t *edir)
841 {
842 	swp_entry_t *ptr;
843 
844 	for (ptr = dir; ptr < edir; ptr++) {
845 		if (ptr->val == entry.val)
846 			return ptr - dir;
847 	}
848 	return -1;
849 }
850 
851 static int shmem_unuse_inode(struct shmem_inode_info *info, swp_entry_t entry, struct page *page)
852 {
853 	struct inode *inode;
854 	unsigned long idx;
855 	unsigned long size;
856 	unsigned long limit;
857 	unsigned long stage;
858 	struct page **dir;
859 	struct page *subdir;
860 	swp_entry_t *ptr;
861 	int offset;
862 	int error;
863 
864 	idx = 0;
865 	ptr = info->i_direct;
866 	spin_lock(&info->lock);
867 	if (!info->swapped) {
868 		list_del_init(&info->swaplist);
869 		goto lost2;
870 	}
871 	limit = info->next_index;
872 	size = limit;
873 	if (size > SHMEM_NR_DIRECT)
874 		size = SHMEM_NR_DIRECT;
875 	offset = shmem_find_swp(entry, ptr, ptr+size);
876 	if (offset >= 0)
877 		goto found;
878 	if (!info->i_indirect)
879 		goto lost2;
880 
881 	dir = shmem_dir_map(info->i_indirect);
882 	stage = SHMEM_NR_DIRECT + ENTRIES_PER_PAGEPAGE/2;
883 
884 	for (idx = SHMEM_NR_DIRECT; idx < limit; idx += ENTRIES_PER_PAGE, dir++) {
885 		if (unlikely(idx == stage)) {
886 			shmem_dir_unmap(dir-1);
887 			if (cond_resched_lock(&info->lock)) {
888 				/* check it has not been truncated */
889 				if (limit > info->next_index) {
890 					limit = info->next_index;
891 					if (idx >= limit)
892 						goto lost2;
893 				}
894 			}
895 			dir = shmem_dir_map(info->i_indirect) +
896 			    ENTRIES_PER_PAGE/2 + idx/ENTRIES_PER_PAGEPAGE;
897 			while (!*dir) {
898 				dir++;
899 				idx += ENTRIES_PER_PAGEPAGE;
900 				if (idx >= limit)
901 					goto lost1;
902 			}
903 			stage = idx + ENTRIES_PER_PAGEPAGE;
904 			subdir = *dir;
905 			shmem_dir_unmap(dir);
906 			dir = shmem_dir_map(subdir);
907 		}
908 		subdir = *dir;
909 		if (subdir && page_private(subdir)) {
910 			ptr = shmem_swp_map(subdir);
911 			size = limit - idx;
912 			if (size > ENTRIES_PER_PAGE)
913 				size = ENTRIES_PER_PAGE;
914 			offset = shmem_find_swp(entry, ptr, ptr+size);
915 			shmem_swp_unmap(ptr);
916 			if (offset >= 0) {
917 				shmem_dir_unmap(dir);
918 				goto found;
919 			}
920 		}
921 	}
922 lost1:
923 	shmem_dir_unmap(dir-1);
924 lost2:
925 	spin_unlock(&info->lock);
926 	return 0;
927 found:
928 	idx += offset;
929 	inode = igrab(&info->vfs_inode);
930 	spin_unlock(&info->lock);
931 
932 	/*
933 	 * Move _head_ to start search for next from here.
934 	 * But be careful: shmem_delete_inode checks list_empty without taking
935 	 * mutex, and there's an instant in list_move_tail when info->swaplist
936 	 * would appear empty, if it were the only one on shmem_swaplist.  We
937 	 * could avoid doing it if inode NULL; or use this minor optimization.
938 	 */
939 	if (shmem_swaplist.next != &info->swaplist)
940 		list_move_tail(&shmem_swaplist, &info->swaplist);
941 	mutex_unlock(&shmem_swaplist_mutex);
942 
943 	error = 1;
944 	if (!inode)
945 		goto out;
946 	/*
947 	 * Charge page using GFP_KERNEL while we can wait.
948 	 * Charged back to the user(not to caller) when swap account is used.
949 	 * add_to_page_cache() will be called with GFP_NOWAIT.
950 	 */
951 	error = mem_cgroup_cache_charge(page, current->mm, GFP_KERNEL);
952 	if (error)
953 		goto out;
954 	error = radix_tree_preload(GFP_KERNEL);
955 	if (error) {
956 		mem_cgroup_uncharge_cache_page(page);
957 		goto out;
958 	}
959 	error = 1;
960 
961 	spin_lock(&info->lock);
962 	ptr = shmem_swp_entry(info, idx, NULL);
963 	if (ptr && ptr->val == entry.val) {
964 		error = add_to_page_cache_locked(page, inode->i_mapping,
965 						idx, GFP_NOWAIT);
966 		/* does mem_cgroup_uncharge_cache_page on error */
967 	} else	/* we must compensate for our precharge above */
968 		mem_cgroup_uncharge_cache_page(page);
969 
970 	if (error == -EEXIST) {
971 		struct page *filepage = find_get_page(inode->i_mapping, idx);
972 		error = 1;
973 		if (filepage) {
974 			/*
975 			 * There might be a more uptodate page coming down
976 			 * from a stacked writepage: forget our swappage if so.
977 			 */
978 			if (PageUptodate(filepage))
979 				error = 0;
980 			page_cache_release(filepage);
981 		}
982 	}
983 	if (!error) {
984 		delete_from_swap_cache(page);
985 		set_page_dirty(page);
986 		info->flags |= SHMEM_PAGEIN;
987 		shmem_swp_set(info, ptr, 0);
988 		swap_free(entry);
989 		error = 1;	/* not an error, but entry was found */
990 	}
991 	if (ptr)
992 		shmem_swp_unmap(ptr);
993 	spin_unlock(&info->lock);
994 	radix_tree_preload_end();
995 out:
996 	unlock_page(page);
997 	page_cache_release(page);
998 	iput(inode);		/* allows for NULL */
999 	return error;
1000 }
1001 
1002 /*
1003  * shmem_unuse() search for an eventually swapped out shmem page.
1004  */
1005 int shmem_unuse(swp_entry_t entry, struct page *page)
1006 {
1007 	struct list_head *p, *next;
1008 	struct shmem_inode_info *info;
1009 	int found = 0;
1010 
1011 	mutex_lock(&shmem_swaplist_mutex);
1012 	list_for_each_safe(p, next, &shmem_swaplist) {
1013 		info = list_entry(p, struct shmem_inode_info, swaplist);
1014 		found = shmem_unuse_inode(info, entry, page);
1015 		cond_resched();
1016 		if (found)
1017 			goto out;
1018 	}
1019 	mutex_unlock(&shmem_swaplist_mutex);
1020 	/*
1021 	 * Can some race bring us here?  We've been holding page lock,
1022 	 * so I think not; but would rather try again later than BUG()
1023 	 */
1024 	unlock_page(page);
1025 	page_cache_release(page);
1026 out:
1027 	return (found < 0) ? found : 0;
1028 }
1029 
1030 /*
1031  * Move the page from the page cache to the swap cache.
1032  */
1033 static int shmem_writepage(struct page *page, struct writeback_control *wbc)
1034 {
1035 	struct shmem_inode_info *info;
1036 	swp_entry_t *entry, swap;
1037 	struct address_space *mapping;
1038 	unsigned long index;
1039 	struct inode *inode;
1040 
1041 	BUG_ON(!PageLocked(page));
1042 	mapping = page->mapping;
1043 	index = page->index;
1044 	inode = mapping->host;
1045 	info = SHMEM_I(inode);
1046 	if (info->flags & VM_LOCKED)
1047 		goto redirty;
1048 	if (!total_swap_pages)
1049 		goto redirty;
1050 
1051 	/*
1052 	 * shmem_backing_dev_info's capabilities prevent regular writeback or
1053 	 * sync from ever calling shmem_writepage; but a stacking filesystem
1054 	 * may use the ->writepage of its underlying filesystem, in which case
1055 	 * tmpfs should write out to swap only in response to memory pressure,
1056 	 * and not for the writeback threads or sync.  However, in those cases,
1057 	 * we do still want to check if there's a redundant swappage to be
1058 	 * discarded.
1059 	 */
1060 	if (wbc->for_reclaim)
1061 		swap = get_swap_page();
1062 	else
1063 		swap.val = 0;
1064 
1065 	spin_lock(&info->lock);
1066 	if (index >= info->next_index) {
1067 		BUG_ON(!(info->flags & SHMEM_TRUNCATE));
1068 		goto unlock;
1069 	}
1070 	entry = shmem_swp_entry(info, index, NULL);
1071 	if (entry->val) {
1072 		/*
1073 		 * The more uptodate page coming down from a stacked
1074 		 * writepage should replace our old swappage.
1075 		 */
1076 		free_swap_and_cache(*entry);
1077 		shmem_swp_set(info, entry, 0);
1078 	}
1079 	shmem_recalc_inode(inode);
1080 
1081 	if (swap.val && add_to_swap_cache(page, swap, GFP_ATOMIC) == 0) {
1082 		remove_from_page_cache(page);
1083 		shmem_swp_set(info, entry, swap.val);
1084 		shmem_swp_unmap(entry);
1085 		if (list_empty(&info->swaplist))
1086 			inode = igrab(inode);
1087 		else
1088 			inode = NULL;
1089 		spin_unlock(&info->lock);
1090 		swap_shmem_alloc(swap);
1091 		BUG_ON(page_mapped(page));
1092 		page_cache_release(page);	/* pagecache ref */
1093 		swap_writepage(page, wbc);
1094 		if (inode) {
1095 			mutex_lock(&shmem_swaplist_mutex);
1096 			/* move instead of add in case we're racing */
1097 			list_move_tail(&info->swaplist, &shmem_swaplist);
1098 			mutex_unlock(&shmem_swaplist_mutex);
1099 			iput(inode);
1100 		}
1101 		return 0;
1102 	}
1103 
1104 	shmem_swp_unmap(entry);
1105 unlock:
1106 	spin_unlock(&info->lock);
1107 	/*
1108 	 * add_to_swap_cache() doesn't return -EEXIST, so we can safely
1109 	 * clear SWAP_HAS_CACHE flag.
1110 	 */
1111 	swapcache_free(swap, NULL);
1112 redirty:
1113 	set_page_dirty(page);
1114 	if (wbc->for_reclaim)
1115 		return AOP_WRITEPAGE_ACTIVATE;	/* Return with page locked */
1116 	unlock_page(page);
1117 	return 0;
1118 }
1119 
1120 #ifdef CONFIG_NUMA
1121 #ifdef CONFIG_TMPFS
1122 static void shmem_show_mpol(struct seq_file *seq, struct mempolicy *mpol)
1123 {
1124 	char buffer[64];
1125 
1126 	if (!mpol || mpol->mode == MPOL_DEFAULT)
1127 		return;		/* show nothing */
1128 
1129 	mpol_to_str(buffer, sizeof(buffer), mpol, 1);
1130 
1131 	seq_printf(seq, ",mpol=%s", buffer);
1132 }
1133 
1134 static struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
1135 {
1136 	struct mempolicy *mpol = NULL;
1137 	if (sbinfo->mpol) {
1138 		spin_lock(&sbinfo->stat_lock);	/* prevent replace/use races */
1139 		mpol = sbinfo->mpol;
1140 		mpol_get(mpol);
1141 		spin_unlock(&sbinfo->stat_lock);
1142 	}
1143 	return mpol;
1144 }
1145 #endif /* CONFIG_TMPFS */
1146 
1147 static struct page *shmem_swapin(swp_entry_t entry, gfp_t gfp,
1148 			struct shmem_inode_info *info, unsigned long idx)
1149 {
1150 	struct mempolicy mpol, *spol;
1151 	struct vm_area_struct pvma;
1152 	struct page *page;
1153 
1154 	spol = mpol_cond_copy(&mpol,
1155 				mpol_shared_policy_lookup(&info->policy, idx));
1156 
1157 	/* Create a pseudo vma that just contains the policy */
1158 	pvma.vm_start = 0;
1159 	pvma.vm_pgoff = idx;
1160 	pvma.vm_ops = NULL;
1161 	pvma.vm_policy = spol;
1162 	page = swapin_readahead(entry, gfp, &pvma, 0);
1163 	return page;
1164 }
1165 
1166 static struct page *shmem_alloc_page(gfp_t gfp,
1167 			struct shmem_inode_info *info, unsigned long idx)
1168 {
1169 	struct vm_area_struct pvma;
1170 
1171 	/* Create a pseudo vma that just contains the policy */
1172 	pvma.vm_start = 0;
1173 	pvma.vm_pgoff = idx;
1174 	pvma.vm_ops = NULL;
1175 	pvma.vm_policy = mpol_shared_policy_lookup(&info->policy, idx);
1176 
1177 	/*
1178 	 * alloc_page_vma() will drop the shared policy reference
1179 	 */
1180 	return alloc_page_vma(gfp, &pvma, 0);
1181 }
1182 #else /* !CONFIG_NUMA */
1183 #ifdef CONFIG_TMPFS
1184 static inline void shmem_show_mpol(struct seq_file *seq, struct mempolicy *p)
1185 {
1186 }
1187 #endif /* CONFIG_TMPFS */
1188 
1189 static inline struct page *shmem_swapin(swp_entry_t entry, gfp_t gfp,
1190 			struct shmem_inode_info *info, unsigned long idx)
1191 {
1192 	return swapin_readahead(entry, gfp, NULL, 0);
1193 }
1194 
1195 static inline struct page *shmem_alloc_page(gfp_t gfp,
1196 			struct shmem_inode_info *info, unsigned long idx)
1197 {
1198 	return alloc_page(gfp);
1199 }
1200 #endif /* CONFIG_NUMA */
1201 
1202 #if !defined(CONFIG_NUMA) || !defined(CONFIG_TMPFS)
1203 static inline struct mempolicy *shmem_get_sbmpol(struct shmem_sb_info *sbinfo)
1204 {
1205 	return NULL;
1206 }
1207 #endif
1208 
1209 /*
1210  * shmem_getpage - either get the page from swap or allocate a new one
1211  *
1212  * If we allocate a new one we do not mark it dirty. That's up to the
1213  * vm. If we swap it in we mark it dirty since we also free the swap
1214  * entry since a page cannot live in both the swap and page cache
1215  */
1216 static int shmem_getpage(struct inode *inode, unsigned long idx,
1217 			struct page **pagep, enum sgp_type sgp, int *type)
1218 {
1219 	struct address_space *mapping = inode->i_mapping;
1220 	struct shmem_inode_info *info = SHMEM_I(inode);
1221 	struct shmem_sb_info *sbinfo;
1222 	struct page *filepage = *pagep;
1223 	struct page *swappage;
1224 	swp_entry_t *entry;
1225 	swp_entry_t swap;
1226 	gfp_t gfp;
1227 	int error;
1228 
1229 	if (idx >= SHMEM_MAX_INDEX)
1230 		return -EFBIG;
1231 
1232 	if (type)
1233 		*type = 0;
1234 
1235 	/*
1236 	 * Normally, filepage is NULL on entry, and either found
1237 	 * uptodate immediately, or allocated and zeroed, or read
1238 	 * in under swappage, which is then assigned to filepage.
1239 	 * But shmem_readpage (required for splice) passes in a locked
1240 	 * filepage, which may be found not uptodate by other callers
1241 	 * too, and may need to be copied from the swappage read in.
1242 	 */
1243 repeat:
1244 	if (!filepage)
1245 		filepage = find_lock_page(mapping, idx);
1246 	if (filepage && PageUptodate(filepage))
1247 		goto done;
1248 	error = 0;
1249 	gfp = mapping_gfp_mask(mapping);
1250 	if (!filepage) {
1251 		/*
1252 		 * Try to preload while we can wait, to not make a habit of
1253 		 * draining atomic reserves; but don't latch on to this cpu.
1254 		 */
1255 		error = radix_tree_preload(gfp & ~__GFP_HIGHMEM);
1256 		if (error)
1257 			goto failed;
1258 		radix_tree_preload_end();
1259 	}
1260 
1261 	spin_lock(&info->lock);
1262 	shmem_recalc_inode(inode);
1263 	entry = shmem_swp_alloc(info, idx, sgp);
1264 	if (IS_ERR(entry)) {
1265 		spin_unlock(&info->lock);
1266 		error = PTR_ERR(entry);
1267 		goto failed;
1268 	}
1269 	swap = *entry;
1270 
1271 	if (swap.val) {
1272 		/* Look it up and read it in.. */
1273 		swappage = lookup_swap_cache(swap);
1274 		if (!swappage) {
1275 			shmem_swp_unmap(entry);
1276 			/* here we actually do the io */
1277 			if (type && !(*type & VM_FAULT_MAJOR)) {
1278 				__count_vm_event(PGMAJFAULT);
1279 				*type |= VM_FAULT_MAJOR;
1280 			}
1281 			spin_unlock(&info->lock);
1282 			swappage = shmem_swapin(swap, gfp, info, idx);
1283 			if (!swappage) {
1284 				spin_lock(&info->lock);
1285 				entry = shmem_swp_alloc(info, idx, sgp);
1286 				if (IS_ERR(entry))
1287 					error = PTR_ERR(entry);
1288 				else {
1289 					if (entry->val == swap.val)
1290 						error = -ENOMEM;
1291 					shmem_swp_unmap(entry);
1292 				}
1293 				spin_unlock(&info->lock);
1294 				if (error)
1295 					goto failed;
1296 				goto repeat;
1297 			}
1298 			wait_on_page_locked(swappage);
1299 			page_cache_release(swappage);
1300 			goto repeat;
1301 		}
1302 
1303 		/* We have to do this with page locked to prevent races */
1304 		if (!trylock_page(swappage)) {
1305 			shmem_swp_unmap(entry);
1306 			spin_unlock(&info->lock);
1307 			wait_on_page_locked(swappage);
1308 			page_cache_release(swappage);
1309 			goto repeat;
1310 		}
1311 		if (PageWriteback(swappage)) {
1312 			shmem_swp_unmap(entry);
1313 			spin_unlock(&info->lock);
1314 			wait_on_page_writeback(swappage);
1315 			unlock_page(swappage);
1316 			page_cache_release(swappage);
1317 			goto repeat;
1318 		}
1319 		if (!PageUptodate(swappage)) {
1320 			shmem_swp_unmap(entry);
1321 			spin_unlock(&info->lock);
1322 			unlock_page(swappage);
1323 			page_cache_release(swappage);
1324 			error = -EIO;
1325 			goto failed;
1326 		}
1327 
1328 		if (filepage) {
1329 			shmem_swp_set(info, entry, 0);
1330 			shmem_swp_unmap(entry);
1331 			delete_from_swap_cache(swappage);
1332 			spin_unlock(&info->lock);
1333 			copy_highpage(filepage, swappage);
1334 			unlock_page(swappage);
1335 			page_cache_release(swappage);
1336 			flush_dcache_page(filepage);
1337 			SetPageUptodate(filepage);
1338 			set_page_dirty(filepage);
1339 			swap_free(swap);
1340 		} else if (!(error = add_to_page_cache_locked(swappage, mapping,
1341 					idx, GFP_NOWAIT))) {
1342 			info->flags |= SHMEM_PAGEIN;
1343 			shmem_swp_set(info, entry, 0);
1344 			shmem_swp_unmap(entry);
1345 			delete_from_swap_cache(swappage);
1346 			spin_unlock(&info->lock);
1347 			filepage = swappage;
1348 			set_page_dirty(filepage);
1349 			swap_free(swap);
1350 		} else {
1351 			shmem_swp_unmap(entry);
1352 			spin_unlock(&info->lock);
1353 			if (error == -ENOMEM) {
1354 				/*
1355 				 * reclaim from proper memory cgroup and
1356 				 * call memcg's OOM if needed.
1357 				 */
1358 				error = mem_cgroup_shmem_charge_fallback(
1359 								swappage,
1360 								current->mm,
1361 								gfp);
1362 				if (error) {
1363 					unlock_page(swappage);
1364 					page_cache_release(swappage);
1365 					goto failed;
1366 				}
1367 			}
1368 			unlock_page(swappage);
1369 			page_cache_release(swappage);
1370 			goto repeat;
1371 		}
1372 	} else if (sgp == SGP_READ && !filepage) {
1373 		shmem_swp_unmap(entry);
1374 		filepage = find_get_page(mapping, idx);
1375 		if (filepage &&
1376 		    (!PageUptodate(filepage) || !trylock_page(filepage))) {
1377 			spin_unlock(&info->lock);
1378 			wait_on_page_locked(filepage);
1379 			page_cache_release(filepage);
1380 			filepage = NULL;
1381 			goto repeat;
1382 		}
1383 		spin_unlock(&info->lock);
1384 	} else {
1385 		shmem_swp_unmap(entry);
1386 		sbinfo = SHMEM_SB(inode->i_sb);
1387 		if (sbinfo->max_blocks) {
1388 			spin_lock(&sbinfo->stat_lock);
1389 			if (sbinfo->free_blocks == 0 ||
1390 			    shmem_acct_block(info->flags)) {
1391 				spin_unlock(&sbinfo->stat_lock);
1392 				spin_unlock(&info->lock);
1393 				error = -ENOSPC;
1394 				goto failed;
1395 			}
1396 			sbinfo->free_blocks--;
1397 			inode->i_blocks += BLOCKS_PER_PAGE;
1398 			spin_unlock(&sbinfo->stat_lock);
1399 		} else if (shmem_acct_block(info->flags)) {
1400 			spin_unlock(&info->lock);
1401 			error = -ENOSPC;
1402 			goto failed;
1403 		}
1404 
1405 		if (!filepage) {
1406 			int ret;
1407 
1408 			spin_unlock(&info->lock);
1409 			filepage = shmem_alloc_page(gfp, info, idx);
1410 			if (!filepage) {
1411 				shmem_unacct_blocks(info->flags, 1);
1412 				shmem_free_blocks(inode, 1);
1413 				error = -ENOMEM;
1414 				goto failed;
1415 			}
1416 			SetPageSwapBacked(filepage);
1417 
1418 			/* Precharge page while we can wait, compensate after */
1419 			error = mem_cgroup_cache_charge(filepage, current->mm,
1420 					GFP_KERNEL);
1421 			if (error) {
1422 				page_cache_release(filepage);
1423 				shmem_unacct_blocks(info->flags, 1);
1424 				shmem_free_blocks(inode, 1);
1425 				filepage = NULL;
1426 				goto failed;
1427 			}
1428 
1429 			spin_lock(&info->lock);
1430 			entry = shmem_swp_alloc(info, idx, sgp);
1431 			if (IS_ERR(entry))
1432 				error = PTR_ERR(entry);
1433 			else {
1434 				swap = *entry;
1435 				shmem_swp_unmap(entry);
1436 			}
1437 			ret = error || swap.val;
1438 			if (ret)
1439 				mem_cgroup_uncharge_cache_page(filepage);
1440 			else
1441 				ret = add_to_page_cache_lru(filepage, mapping,
1442 						idx, GFP_NOWAIT);
1443 			/*
1444 			 * At add_to_page_cache_lru() failure, uncharge will
1445 			 * be done automatically.
1446 			 */
1447 			if (ret) {
1448 				spin_unlock(&info->lock);
1449 				page_cache_release(filepage);
1450 				shmem_unacct_blocks(info->flags, 1);
1451 				shmem_free_blocks(inode, 1);
1452 				filepage = NULL;
1453 				if (error)
1454 					goto failed;
1455 				goto repeat;
1456 			}
1457 			info->flags |= SHMEM_PAGEIN;
1458 		}
1459 
1460 		info->alloced++;
1461 		spin_unlock(&info->lock);
1462 		clear_highpage(filepage);
1463 		flush_dcache_page(filepage);
1464 		SetPageUptodate(filepage);
1465 		if (sgp == SGP_DIRTY)
1466 			set_page_dirty(filepage);
1467 	}
1468 done:
1469 	*pagep = filepage;
1470 	return 0;
1471 
1472 failed:
1473 	if (*pagep != filepage) {
1474 		unlock_page(filepage);
1475 		page_cache_release(filepage);
1476 	}
1477 	return error;
1478 }
1479 
1480 static int shmem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
1481 {
1482 	struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
1483 	int error;
1484 	int ret;
1485 
1486 	if (((loff_t)vmf->pgoff << PAGE_CACHE_SHIFT) >= i_size_read(inode))
1487 		return VM_FAULT_SIGBUS;
1488 
1489 	error = shmem_getpage(inode, vmf->pgoff, &vmf->page, SGP_CACHE, &ret);
1490 	if (error)
1491 		return ((error == -ENOMEM) ? VM_FAULT_OOM : VM_FAULT_SIGBUS);
1492 
1493 	return ret | VM_FAULT_LOCKED;
1494 }
1495 
1496 #ifdef CONFIG_NUMA
1497 static int shmem_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
1498 {
1499 	struct inode *i = vma->vm_file->f_path.dentry->d_inode;
1500 	return mpol_set_shared_policy(&SHMEM_I(i)->policy, vma, new);
1501 }
1502 
1503 static struct mempolicy *shmem_get_policy(struct vm_area_struct *vma,
1504 					  unsigned long addr)
1505 {
1506 	struct inode *i = vma->vm_file->f_path.dentry->d_inode;
1507 	unsigned long idx;
1508 
1509 	idx = ((addr - vma->vm_start) >> PAGE_SHIFT) + vma->vm_pgoff;
1510 	return mpol_shared_policy_lookup(&SHMEM_I(i)->policy, idx);
1511 }
1512 #endif
1513 
1514 int shmem_lock(struct file *file, int lock, struct user_struct *user)
1515 {
1516 	struct inode *inode = file->f_path.dentry->d_inode;
1517 	struct shmem_inode_info *info = SHMEM_I(inode);
1518 	int retval = -ENOMEM;
1519 
1520 	spin_lock(&info->lock);
1521 	if (lock && !(info->flags & VM_LOCKED)) {
1522 		if (!user_shm_lock(inode->i_size, user))
1523 			goto out_nomem;
1524 		info->flags |= VM_LOCKED;
1525 		mapping_set_unevictable(file->f_mapping);
1526 	}
1527 	if (!lock && (info->flags & VM_LOCKED) && user) {
1528 		user_shm_unlock(inode->i_size, user);
1529 		info->flags &= ~VM_LOCKED;
1530 		mapping_clear_unevictable(file->f_mapping);
1531 		scan_mapping_unevictable_pages(file->f_mapping);
1532 	}
1533 	retval = 0;
1534 
1535 out_nomem:
1536 	spin_unlock(&info->lock);
1537 	return retval;
1538 }
1539 
1540 static int shmem_mmap(struct file *file, struct vm_area_struct *vma)
1541 {
1542 	file_accessed(file);
1543 	vma->vm_ops = &shmem_vm_ops;
1544 	vma->vm_flags |= VM_CAN_NONLINEAR;
1545 	return 0;
1546 }
1547 
1548 static struct inode *shmem_get_inode(struct super_block *sb, int mode,
1549 					dev_t dev, unsigned long flags)
1550 {
1551 	struct inode *inode;
1552 	struct shmem_inode_info *info;
1553 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
1554 
1555 	if (shmem_reserve_inode(sb))
1556 		return NULL;
1557 
1558 	inode = new_inode(sb);
1559 	if (inode) {
1560 		inode->i_mode = mode;
1561 		inode->i_uid = current_fsuid();
1562 		inode->i_gid = current_fsgid();
1563 		inode->i_blocks = 0;
1564 		inode->i_mapping->backing_dev_info = &shmem_backing_dev_info;
1565 		inode->i_atime = inode->i_mtime = inode->i_ctime = CURRENT_TIME;
1566 		inode->i_generation = get_seconds();
1567 		info = SHMEM_I(inode);
1568 		memset(info, 0, (char *)inode - (char *)info);
1569 		spin_lock_init(&info->lock);
1570 		info->flags = flags & VM_NORESERVE;
1571 		INIT_LIST_HEAD(&info->swaplist);
1572 		cache_no_acl(inode);
1573 
1574 		switch (mode & S_IFMT) {
1575 		default:
1576 			inode->i_op = &shmem_special_inode_operations;
1577 			init_special_inode(inode, mode, dev);
1578 			break;
1579 		case S_IFREG:
1580 			inode->i_mapping->a_ops = &shmem_aops;
1581 			inode->i_op = &shmem_inode_operations;
1582 			inode->i_fop = &shmem_file_operations;
1583 			mpol_shared_policy_init(&info->policy,
1584 						 shmem_get_sbmpol(sbinfo));
1585 			break;
1586 		case S_IFDIR:
1587 			inc_nlink(inode);
1588 			/* Some things misbehave if size == 0 on a directory */
1589 			inode->i_size = 2 * BOGO_DIRENT_SIZE;
1590 			inode->i_op = &shmem_dir_inode_operations;
1591 			inode->i_fop = &simple_dir_operations;
1592 			break;
1593 		case S_IFLNK:
1594 			/*
1595 			 * Must not load anything in the rbtree,
1596 			 * mpol_free_shared_policy will not be called.
1597 			 */
1598 			mpol_shared_policy_init(&info->policy, NULL);
1599 			break;
1600 		}
1601 	} else
1602 		shmem_free_inode(sb);
1603 	return inode;
1604 }
1605 
1606 #ifdef CONFIG_TMPFS
1607 static const struct inode_operations shmem_symlink_inode_operations;
1608 static const struct inode_operations shmem_symlink_inline_operations;
1609 
1610 /*
1611  * Normally tmpfs avoids the use of shmem_readpage and shmem_write_begin;
1612  * but providing them allows a tmpfs file to be used for splice, sendfile, and
1613  * below the loop driver, in the generic fashion that many filesystems support.
1614  */
1615 static int shmem_readpage(struct file *file, struct page *page)
1616 {
1617 	struct inode *inode = page->mapping->host;
1618 	int error = shmem_getpage(inode, page->index, &page, SGP_CACHE, NULL);
1619 	unlock_page(page);
1620 	return error;
1621 }
1622 
1623 static int
1624 shmem_write_begin(struct file *file, struct address_space *mapping,
1625 			loff_t pos, unsigned len, unsigned flags,
1626 			struct page **pagep, void **fsdata)
1627 {
1628 	struct inode *inode = mapping->host;
1629 	pgoff_t index = pos >> PAGE_CACHE_SHIFT;
1630 	*pagep = NULL;
1631 	return shmem_getpage(inode, index, pagep, SGP_WRITE, NULL);
1632 }
1633 
1634 static int
1635 shmem_write_end(struct file *file, struct address_space *mapping,
1636 			loff_t pos, unsigned len, unsigned copied,
1637 			struct page *page, void *fsdata)
1638 {
1639 	struct inode *inode = mapping->host;
1640 
1641 	if (pos + copied > inode->i_size)
1642 		i_size_write(inode, pos + copied);
1643 
1644 	set_page_dirty(page);
1645 	unlock_page(page);
1646 	page_cache_release(page);
1647 
1648 	return copied;
1649 }
1650 
1651 static void do_shmem_file_read(struct file *filp, loff_t *ppos, read_descriptor_t *desc, read_actor_t actor)
1652 {
1653 	struct inode *inode = filp->f_path.dentry->d_inode;
1654 	struct address_space *mapping = inode->i_mapping;
1655 	unsigned long index, offset;
1656 	enum sgp_type sgp = SGP_READ;
1657 
1658 	/*
1659 	 * Might this read be for a stacking filesystem?  Then when reading
1660 	 * holes of a sparse file, we actually need to allocate those pages,
1661 	 * and even mark them dirty, so it cannot exceed the max_blocks limit.
1662 	 */
1663 	if (segment_eq(get_fs(), KERNEL_DS))
1664 		sgp = SGP_DIRTY;
1665 
1666 	index = *ppos >> PAGE_CACHE_SHIFT;
1667 	offset = *ppos & ~PAGE_CACHE_MASK;
1668 
1669 	for (;;) {
1670 		struct page *page = NULL;
1671 		unsigned long end_index, nr, ret;
1672 		loff_t i_size = i_size_read(inode);
1673 
1674 		end_index = i_size >> PAGE_CACHE_SHIFT;
1675 		if (index > end_index)
1676 			break;
1677 		if (index == end_index) {
1678 			nr = i_size & ~PAGE_CACHE_MASK;
1679 			if (nr <= offset)
1680 				break;
1681 		}
1682 
1683 		desc->error = shmem_getpage(inode, index, &page, sgp, NULL);
1684 		if (desc->error) {
1685 			if (desc->error == -EINVAL)
1686 				desc->error = 0;
1687 			break;
1688 		}
1689 		if (page)
1690 			unlock_page(page);
1691 
1692 		/*
1693 		 * We must evaluate after, since reads (unlike writes)
1694 		 * are called without i_mutex protection against truncate
1695 		 */
1696 		nr = PAGE_CACHE_SIZE;
1697 		i_size = i_size_read(inode);
1698 		end_index = i_size >> PAGE_CACHE_SHIFT;
1699 		if (index == end_index) {
1700 			nr = i_size & ~PAGE_CACHE_MASK;
1701 			if (nr <= offset) {
1702 				if (page)
1703 					page_cache_release(page);
1704 				break;
1705 			}
1706 		}
1707 		nr -= offset;
1708 
1709 		if (page) {
1710 			/*
1711 			 * If users can be writing to this page using arbitrary
1712 			 * virtual addresses, take care about potential aliasing
1713 			 * before reading the page on the kernel side.
1714 			 */
1715 			if (mapping_writably_mapped(mapping))
1716 				flush_dcache_page(page);
1717 			/*
1718 			 * Mark the page accessed if we read the beginning.
1719 			 */
1720 			if (!offset)
1721 				mark_page_accessed(page);
1722 		} else {
1723 			page = ZERO_PAGE(0);
1724 			page_cache_get(page);
1725 		}
1726 
1727 		/*
1728 		 * Ok, we have the page, and it's up-to-date, so
1729 		 * now we can copy it to user space...
1730 		 *
1731 		 * The actor routine returns how many bytes were actually used..
1732 		 * NOTE! This may not be the same as how much of a user buffer
1733 		 * we filled up (we may be padding etc), so we can only update
1734 		 * "pos" here (the actor routine has to update the user buffer
1735 		 * pointers and the remaining count).
1736 		 */
1737 		ret = actor(desc, page, offset, nr);
1738 		offset += ret;
1739 		index += offset >> PAGE_CACHE_SHIFT;
1740 		offset &= ~PAGE_CACHE_MASK;
1741 
1742 		page_cache_release(page);
1743 		if (ret != nr || !desc->count)
1744 			break;
1745 
1746 		cond_resched();
1747 	}
1748 
1749 	*ppos = ((loff_t) index << PAGE_CACHE_SHIFT) + offset;
1750 	file_accessed(filp);
1751 }
1752 
1753 static ssize_t shmem_file_aio_read(struct kiocb *iocb,
1754 		const struct iovec *iov, unsigned long nr_segs, loff_t pos)
1755 {
1756 	struct file *filp = iocb->ki_filp;
1757 	ssize_t retval;
1758 	unsigned long seg;
1759 	size_t count;
1760 	loff_t *ppos = &iocb->ki_pos;
1761 
1762 	retval = generic_segment_checks(iov, &nr_segs, &count, VERIFY_WRITE);
1763 	if (retval)
1764 		return retval;
1765 
1766 	for (seg = 0; seg < nr_segs; seg++) {
1767 		read_descriptor_t desc;
1768 
1769 		desc.written = 0;
1770 		desc.arg.buf = iov[seg].iov_base;
1771 		desc.count = iov[seg].iov_len;
1772 		if (desc.count == 0)
1773 			continue;
1774 		desc.error = 0;
1775 		do_shmem_file_read(filp, ppos, &desc, file_read_actor);
1776 		retval += desc.written;
1777 		if (desc.error) {
1778 			retval = retval ?: desc.error;
1779 			break;
1780 		}
1781 		if (desc.count > 0)
1782 			break;
1783 	}
1784 	return retval;
1785 }
1786 
1787 static int shmem_statfs(struct dentry *dentry, struct kstatfs *buf)
1788 {
1789 	struct shmem_sb_info *sbinfo = SHMEM_SB(dentry->d_sb);
1790 
1791 	buf->f_type = TMPFS_MAGIC;
1792 	buf->f_bsize = PAGE_CACHE_SIZE;
1793 	buf->f_namelen = NAME_MAX;
1794 	spin_lock(&sbinfo->stat_lock);
1795 	if (sbinfo->max_blocks) {
1796 		buf->f_blocks = sbinfo->max_blocks;
1797 		buf->f_bavail = buf->f_bfree = sbinfo->free_blocks;
1798 	}
1799 	if (sbinfo->max_inodes) {
1800 		buf->f_files = sbinfo->max_inodes;
1801 		buf->f_ffree = sbinfo->free_inodes;
1802 	}
1803 	/* else leave those fields 0 like simple_statfs */
1804 	spin_unlock(&sbinfo->stat_lock);
1805 	return 0;
1806 }
1807 
1808 /*
1809  * File creation. Allocate an inode, and we're done..
1810  */
1811 static int
1812 shmem_mknod(struct inode *dir, struct dentry *dentry, int mode, dev_t dev)
1813 {
1814 	struct inode *inode;
1815 	int error = -ENOSPC;
1816 
1817 	inode = shmem_get_inode(dir->i_sb, mode, dev, VM_NORESERVE);
1818 	if (inode) {
1819 		error = security_inode_init_security(inode, dir, NULL, NULL,
1820 						     NULL);
1821 		if (error) {
1822 			if (error != -EOPNOTSUPP) {
1823 				iput(inode);
1824 				return error;
1825 			}
1826 		}
1827 #ifdef CONFIG_TMPFS_POSIX_ACL
1828 		error = generic_acl_init(inode, dir);
1829 		if (error) {
1830 			iput(inode);
1831 			return error;
1832 		}
1833 #else
1834 		error = 0;
1835 #endif
1836 		if (dir->i_mode & S_ISGID) {
1837 			inode->i_gid = dir->i_gid;
1838 			if (S_ISDIR(mode))
1839 				inode->i_mode |= S_ISGID;
1840 		}
1841 		dir->i_size += BOGO_DIRENT_SIZE;
1842 		dir->i_ctime = dir->i_mtime = CURRENT_TIME;
1843 		d_instantiate(dentry, inode);
1844 		dget(dentry); /* Extra count - pin the dentry in core */
1845 	}
1846 	return error;
1847 }
1848 
1849 static int shmem_mkdir(struct inode *dir, struct dentry *dentry, int mode)
1850 {
1851 	int error;
1852 
1853 	if ((error = shmem_mknod(dir, dentry, mode | S_IFDIR, 0)))
1854 		return error;
1855 	inc_nlink(dir);
1856 	return 0;
1857 }
1858 
1859 static int shmem_create(struct inode *dir, struct dentry *dentry, int mode,
1860 		struct nameidata *nd)
1861 {
1862 	return shmem_mknod(dir, dentry, mode | S_IFREG, 0);
1863 }
1864 
1865 /*
1866  * Link a file..
1867  */
1868 static int shmem_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
1869 {
1870 	struct inode *inode = old_dentry->d_inode;
1871 	int ret;
1872 
1873 	/*
1874 	 * No ordinary (disk based) filesystem counts links as inodes;
1875 	 * but each new link needs a new dentry, pinning lowmem, and
1876 	 * tmpfs dentries cannot be pruned until they are unlinked.
1877 	 */
1878 	ret = shmem_reserve_inode(inode->i_sb);
1879 	if (ret)
1880 		goto out;
1881 
1882 	dir->i_size += BOGO_DIRENT_SIZE;
1883 	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
1884 	inc_nlink(inode);
1885 	atomic_inc(&inode->i_count);	/* New dentry reference */
1886 	dget(dentry);		/* Extra pinning count for the created dentry */
1887 	d_instantiate(dentry, inode);
1888 out:
1889 	return ret;
1890 }
1891 
1892 static int shmem_unlink(struct inode *dir, struct dentry *dentry)
1893 {
1894 	struct inode *inode = dentry->d_inode;
1895 
1896 	if (inode->i_nlink > 1 && !S_ISDIR(inode->i_mode))
1897 		shmem_free_inode(inode->i_sb);
1898 
1899 	dir->i_size -= BOGO_DIRENT_SIZE;
1900 	inode->i_ctime = dir->i_ctime = dir->i_mtime = CURRENT_TIME;
1901 	drop_nlink(inode);
1902 	dput(dentry);	/* Undo the count from "create" - this does all the work */
1903 	return 0;
1904 }
1905 
1906 static int shmem_rmdir(struct inode *dir, struct dentry *dentry)
1907 {
1908 	if (!simple_empty(dentry))
1909 		return -ENOTEMPTY;
1910 
1911 	drop_nlink(dentry->d_inode);
1912 	drop_nlink(dir);
1913 	return shmem_unlink(dir, dentry);
1914 }
1915 
1916 /*
1917  * The VFS layer already does all the dentry stuff for rename,
1918  * we just have to decrement the usage count for the target if
1919  * it exists so that the VFS layer correctly free's it when it
1920  * gets overwritten.
1921  */
1922 static int shmem_rename(struct inode *old_dir, struct dentry *old_dentry, struct inode *new_dir, struct dentry *new_dentry)
1923 {
1924 	struct inode *inode = old_dentry->d_inode;
1925 	int they_are_dirs = S_ISDIR(inode->i_mode);
1926 
1927 	if (!simple_empty(new_dentry))
1928 		return -ENOTEMPTY;
1929 
1930 	if (new_dentry->d_inode) {
1931 		(void) shmem_unlink(new_dir, new_dentry);
1932 		if (they_are_dirs)
1933 			drop_nlink(old_dir);
1934 	} else if (they_are_dirs) {
1935 		drop_nlink(old_dir);
1936 		inc_nlink(new_dir);
1937 	}
1938 
1939 	old_dir->i_size -= BOGO_DIRENT_SIZE;
1940 	new_dir->i_size += BOGO_DIRENT_SIZE;
1941 	old_dir->i_ctime = old_dir->i_mtime =
1942 	new_dir->i_ctime = new_dir->i_mtime =
1943 	inode->i_ctime = CURRENT_TIME;
1944 	return 0;
1945 }
1946 
1947 static int shmem_symlink(struct inode *dir, struct dentry *dentry, const char *symname)
1948 {
1949 	int error;
1950 	int len;
1951 	struct inode *inode;
1952 	struct page *page = NULL;
1953 	char *kaddr;
1954 	struct shmem_inode_info *info;
1955 
1956 	len = strlen(symname) + 1;
1957 	if (len > PAGE_CACHE_SIZE)
1958 		return -ENAMETOOLONG;
1959 
1960 	inode = shmem_get_inode(dir->i_sb, S_IFLNK|S_IRWXUGO, 0, VM_NORESERVE);
1961 	if (!inode)
1962 		return -ENOSPC;
1963 
1964 	error = security_inode_init_security(inode, dir, NULL, NULL,
1965 					     NULL);
1966 	if (error) {
1967 		if (error != -EOPNOTSUPP) {
1968 			iput(inode);
1969 			return error;
1970 		}
1971 		error = 0;
1972 	}
1973 
1974 	info = SHMEM_I(inode);
1975 	inode->i_size = len-1;
1976 	if (len <= (char *)inode - (char *)info) {
1977 		/* do it inline */
1978 		memcpy(info, symname, len);
1979 		inode->i_op = &shmem_symlink_inline_operations;
1980 	} else {
1981 		error = shmem_getpage(inode, 0, &page, SGP_WRITE, NULL);
1982 		if (error) {
1983 			iput(inode);
1984 			return error;
1985 		}
1986 		inode->i_mapping->a_ops = &shmem_aops;
1987 		inode->i_op = &shmem_symlink_inode_operations;
1988 		kaddr = kmap_atomic(page, KM_USER0);
1989 		memcpy(kaddr, symname, len);
1990 		kunmap_atomic(kaddr, KM_USER0);
1991 		set_page_dirty(page);
1992 		unlock_page(page);
1993 		page_cache_release(page);
1994 	}
1995 	if (dir->i_mode & S_ISGID)
1996 		inode->i_gid = dir->i_gid;
1997 	dir->i_size += BOGO_DIRENT_SIZE;
1998 	dir->i_ctime = dir->i_mtime = CURRENT_TIME;
1999 	d_instantiate(dentry, inode);
2000 	dget(dentry);
2001 	return 0;
2002 }
2003 
2004 static void *shmem_follow_link_inline(struct dentry *dentry, struct nameidata *nd)
2005 {
2006 	nd_set_link(nd, (char *)SHMEM_I(dentry->d_inode));
2007 	return NULL;
2008 }
2009 
2010 static void *shmem_follow_link(struct dentry *dentry, struct nameidata *nd)
2011 {
2012 	struct page *page = NULL;
2013 	int res = shmem_getpage(dentry->d_inode, 0, &page, SGP_READ, NULL);
2014 	nd_set_link(nd, res ? ERR_PTR(res) : kmap(page));
2015 	if (page)
2016 		unlock_page(page);
2017 	return page;
2018 }
2019 
2020 static void shmem_put_link(struct dentry *dentry, struct nameidata *nd, void *cookie)
2021 {
2022 	if (!IS_ERR(nd_get_link(nd))) {
2023 		struct page *page = cookie;
2024 		kunmap(page);
2025 		mark_page_accessed(page);
2026 		page_cache_release(page);
2027 	}
2028 }
2029 
2030 static const struct inode_operations shmem_symlink_inline_operations = {
2031 	.readlink	= generic_readlink,
2032 	.follow_link	= shmem_follow_link_inline,
2033 };
2034 
2035 static const struct inode_operations shmem_symlink_inode_operations = {
2036 	.truncate	= shmem_truncate,
2037 	.readlink	= generic_readlink,
2038 	.follow_link	= shmem_follow_link,
2039 	.put_link	= shmem_put_link,
2040 };
2041 
2042 #ifdef CONFIG_TMPFS_POSIX_ACL
2043 /*
2044  * Superblocks without xattr inode operations will get security.* xattr
2045  * support from the VFS "for free". As soon as we have any other xattrs
2046  * like ACLs, we also need to implement the security.* handlers at
2047  * filesystem level, though.
2048  */
2049 
2050 static size_t shmem_xattr_security_list(struct dentry *dentry, char *list,
2051 					size_t list_len, const char *name,
2052 					size_t name_len, int handler_flags)
2053 {
2054 	return security_inode_listsecurity(dentry->d_inode, list, list_len);
2055 }
2056 
2057 static int shmem_xattr_security_get(struct dentry *dentry, const char *name,
2058 		void *buffer, size_t size, int handler_flags)
2059 {
2060 	if (strcmp(name, "") == 0)
2061 		return -EINVAL;
2062 	return xattr_getsecurity(dentry->d_inode, name, buffer, size);
2063 }
2064 
2065 static int shmem_xattr_security_set(struct dentry *dentry, const char *name,
2066 		const void *value, size_t size, int flags, int handler_flags)
2067 {
2068 	if (strcmp(name, "") == 0)
2069 		return -EINVAL;
2070 	return security_inode_setsecurity(dentry->d_inode, name, value,
2071 					  size, flags);
2072 }
2073 
2074 static struct xattr_handler shmem_xattr_security_handler = {
2075 	.prefix = XATTR_SECURITY_PREFIX,
2076 	.list   = shmem_xattr_security_list,
2077 	.get    = shmem_xattr_security_get,
2078 	.set    = shmem_xattr_security_set,
2079 };
2080 
2081 static struct xattr_handler *shmem_xattr_handlers[] = {
2082 	&generic_acl_access_handler,
2083 	&generic_acl_default_handler,
2084 	&shmem_xattr_security_handler,
2085 	NULL
2086 };
2087 #endif
2088 
2089 static struct dentry *shmem_get_parent(struct dentry *child)
2090 {
2091 	return ERR_PTR(-ESTALE);
2092 }
2093 
2094 static int shmem_match(struct inode *ino, void *vfh)
2095 {
2096 	__u32 *fh = vfh;
2097 	__u64 inum = fh[2];
2098 	inum = (inum << 32) | fh[1];
2099 	return ino->i_ino == inum && fh[0] == ino->i_generation;
2100 }
2101 
2102 static struct dentry *shmem_fh_to_dentry(struct super_block *sb,
2103 		struct fid *fid, int fh_len, int fh_type)
2104 {
2105 	struct inode *inode;
2106 	struct dentry *dentry = NULL;
2107 	u64 inum = fid->raw[2];
2108 	inum = (inum << 32) | fid->raw[1];
2109 
2110 	if (fh_len < 3)
2111 		return NULL;
2112 
2113 	inode = ilookup5(sb, (unsigned long)(inum + fid->raw[0]),
2114 			shmem_match, fid->raw);
2115 	if (inode) {
2116 		dentry = d_find_alias(inode);
2117 		iput(inode);
2118 	}
2119 
2120 	return dentry;
2121 }
2122 
2123 static int shmem_encode_fh(struct dentry *dentry, __u32 *fh, int *len,
2124 				int connectable)
2125 {
2126 	struct inode *inode = dentry->d_inode;
2127 
2128 	if (*len < 3)
2129 		return 255;
2130 
2131 	if (hlist_unhashed(&inode->i_hash)) {
2132 		/* Unfortunately insert_inode_hash is not idempotent,
2133 		 * so as we hash inodes here rather than at creation
2134 		 * time, we need a lock to ensure we only try
2135 		 * to do it once
2136 		 */
2137 		static DEFINE_SPINLOCK(lock);
2138 		spin_lock(&lock);
2139 		if (hlist_unhashed(&inode->i_hash))
2140 			__insert_inode_hash(inode,
2141 					    inode->i_ino + inode->i_generation);
2142 		spin_unlock(&lock);
2143 	}
2144 
2145 	fh[0] = inode->i_generation;
2146 	fh[1] = inode->i_ino;
2147 	fh[2] = ((__u64)inode->i_ino) >> 32;
2148 
2149 	*len = 3;
2150 	return 1;
2151 }
2152 
2153 static const struct export_operations shmem_export_ops = {
2154 	.get_parent     = shmem_get_parent,
2155 	.encode_fh      = shmem_encode_fh,
2156 	.fh_to_dentry	= shmem_fh_to_dentry,
2157 };
2158 
2159 static int shmem_parse_options(char *options, struct shmem_sb_info *sbinfo,
2160 			       bool remount)
2161 {
2162 	char *this_char, *value, *rest;
2163 
2164 	while (options != NULL) {
2165 		this_char = options;
2166 		for (;;) {
2167 			/*
2168 			 * NUL-terminate this option: unfortunately,
2169 			 * mount options form a comma-separated list,
2170 			 * but mpol's nodelist may also contain commas.
2171 			 */
2172 			options = strchr(options, ',');
2173 			if (options == NULL)
2174 				break;
2175 			options++;
2176 			if (!isdigit(*options)) {
2177 				options[-1] = '\0';
2178 				break;
2179 			}
2180 		}
2181 		if (!*this_char)
2182 			continue;
2183 		if ((value = strchr(this_char,'=')) != NULL) {
2184 			*value++ = 0;
2185 		} else {
2186 			printk(KERN_ERR
2187 			    "tmpfs: No value for mount option '%s'\n",
2188 			    this_char);
2189 			return 1;
2190 		}
2191 
2192 		if (!strcmp(this_char,"size")) {
2193 			unsigned long long size;
2194 			size = memparse(value,&rest);
2195 			if (*rest == '%') {
2196 				size <<= PAGE_SHIFT;
2197 				size *= totalram_pages;
2198 				do_div(size, 100);
2199 				rest++;
2200 			}
2201 			if (*rest)
2202 				goto bad_val;
2203 			sbinfo->max_blocks =
2204 				DIV_ROUND_UP(size, PAGE_CACHE_SIZE);
2205 		} else if (!strcmp(this_char,"nr_blocks")) {
2206 			sbinfo->max_blocks = memparse(value, &rest);
2207 			if (*rest)
2208 				goto bad_val;
2209 		} else if (!strcmp(this_char,"nr_inodes")) {
2210 			sbinfo->max_inodes = memparse(value, &rest);
2211 			if (*rest)
2212 				goto bad_val;
2213 		} else if (!strcmp(this_char,"mode")) {
2214 			if (remount)
2215 				continue;
2216 			sbinfo->mode = simple_strtoul(value, &rest, 8) & 07777;
2217 			if (*rest)
2218 				goto bad_val;
2219 		} else if (!strcmp(this_char,"uid")) {
2220 			if (remount)
2221 				continue;
2222 			sbinfo->uid = simple_strtoul(value, &rest, 0);
2223 			if (*rest)
2224 				goto bad_val;
2225 		} else if (!strcmp(this_char,"gid")) {
2226 			if (remount)
2227 				continue;
2228 			sbinfo->gid = simple_strtoul(value, &rest, 0);
2229 			if (*rest)
2230 				goto bad_val;
2231 		} else if (!strcmp(this_char,"mpol")) {
2232 			if (mpol_parse_str(value, &sbinfo->mpol, 1))
2233 				goto bad_val;
2234 		} else {
2235 			printk(KERN_ERR "tmpfs: Bad mount option %s\n",
2236 			       this_char);
2237 			return 1;
2238 		}
2239 	}
2240 	return 0;
2241 
2242 bad_val:
2243 	printk(KERN_ERR "tmpfs: Bad value '%s' for mount option '%s'\n",
2244 	       value, this_char);
2245 	return 1;
2246 
2247 }
2248 
2249 static int shmem_remount_fs(struct super_block *sb, int *flags, char *data)
2250 {
2251 	struct shmem_sb_info *sbinfo = SHMEM_SB(sb);
2252 	struct shmem_sb_info config = *sbinfo;
2253 	unsigned long blocks;
2254 	unsigned long inodes;
2255 	int error = -EINVAL;
2256 
2257 	if (shmem_parse_options(data, &config, true))
2258 		return error;
2259 
2260 	spin_lock(&sbinfo->stat_lock);
2261 	blocks = sbinfo->max_blocks - sbinfo->free_blocks;
2262 	inodes = sbinfo->max_inodes - sbinfo->free_inodes;
2263 	if (config.max_blocks < blocks)
2264 		goto out;
2265 	if (config.max_inodes < inodes)
2266 		goto out;
2267 	/*
2268 	 * Those tests also disallow limited->unlimited while any are in
2269 	 * use, so i_blocks will always be zero when max_blocks is zero;
2270 	 * but we must separately disallow unlimited->limited, because
2271 	 * in that case we have no record of how much is already in use.
2272 	 */
2273 	if (config.max_blocks && !sbinfo->max_blocks)
2274 		goto out;
2275 	if (config.max_inodes && !sbinfo->max_inodes)
2276 		goto out;
2277 
2278 	error = 0;
2279 	sbinfo->max_blocks  = config.max_blocks;
2280 	sbinfo->free_blocks = config.max_blocks - blocks;
2281 	sbinfo->max_inodes  = config.max_inodes;
2282 	sbinfo->free_inodes = config.max_inodes - inodes;
2283 
2284 	mpol_put(sbinfo->mpol);
2285 	sbinfo->mpol        = config.mpol;	/* transfers initial ref */
2286 out:
2287 	spin_unlock(&sbinfo->stat_lock);
2288 	return error;
2289 }
2290 
2291 static int shmem_show_options(struct seq_file *seq, struct vfsmount *vfs)
2292 {
2293 	struct shmem_sb_info *sbinfo = SHMEM_SB(vfs->mnt_sb);
2294 
2295 	if (sbinfo->max_blocks != shmem_default_max_blocks())
2296 		seq_printf(seq, ",size=%luk",
2297 			sbinfo->max_blocks << (PAGE_CACHE_SHIFT - 10));
2298 	if (sbinfo->max_inodes != shmem_default_max_inodes())
2299 		seq_printf(seq, ",nr_inodes=%lu", sbinfo->max_inodes);
2300 	if (sbinfo->mode != (S_IRWXUGO | S_ISVTX))
2301 		seq_printf(seq, ",mode=%03o", sbinfo->mode);
2302 	if (sbinfo->uid != 0)
2303 		seq_printf(seq, ",uid=%u", sbinfo->uid);
2304 	if (sbinfo->gid != 0)
2305 		seq_printf(seq, ",gid=%u", sbinfo->gid);
2306 	shmem_show_mpol(seq, sbinfo->mpol);
2307 	return 0;
2308 }
2309 #endif /* CONFIG_TMPFS */
2310 
2311 static void shmem_put_super(struct super_block *sb)
2312 {
2313 	kfree(sb->s_fs_info);
2314 	sb->s_fs_info = NULL;
2315 }
2316 
2317 int shmem_fill_super(struct super_block *sb, void *data, int silent)
2318 {
2319 	struct inode *inode;
2320 	struct dentry *root;
2321 	struct shmem_sb_info *sbinfo;
2322 	int err = -ENOMEM;
2323 
2324 	/* Round up to L1_CACHE_BYTES to resist false sharing */
2325 	sbinfo = kzalloc(max((int)sizeof(struct shmem_sb_info),
2326 				L1_CACHE_BYTES), GFP_KERNEL);
2327 	if (!sbinfo)
2328 		return -ENOMEM;
2329 
2330 	sbinfo->mode = S_IRWXUGO | S_ISVTX;
2331 	sbinfo->uid = current_fsuid();
2332 	sbinfo->gid = current_fsgid();
2333 	sb->s_fs_info = sbinfo;
2334 
2335 #ifdef CONFIG_TMPFS
2336 	/*
2337 	 * Per default we only allow half of the physical ram per
2338 	 * tmpfs instance, limiting inodes to one per page of lowmem;
2339 	 * but the internal instance is left unlimited.
2340 	 */
2341 	if (!(sb->s_flags & MS_NOUSER)) {
2342 		sbinfo->max_blocks = shmem_default_max_blocks();
2343 		sbinfo->max_inodes = shmem_default_max_inodes();
2344 		if (shmem_parse_options(data, sbinfo, false)) {
2345 			err = -EINVAL;
2346 			goto failed;
2347 		}
2348 	}
2349 	sb->s_export_op = &shmem_export_ops;
2350 #else
2351 	sb->s_flags |= MS_NOUSER;
2352 #endif
2353 
2354 	spin_lock_init(&sbinfo->stat_lock);
2355 	sbinfo->free_blocks = sbinfo->max_blocks;
2356 	sbinfo->free_inodes = sbinfo->max_inodes;
2357 
2358 	sb->s_maxbytes = SHMEM_MAX_BYTES;
2359 	sb->s_blocksize = PAGE_CACHE_SIZE;
2360 	sb->s_blocksize_bits = PAGE_CACHE_SHIFT;
2361 	sb->s_magic = TMPFS_MAGIC;
2362 	sb->s_op = &shmem_ops;
2363 	sb->s_time_gran = 1;
2364 #ifdef CONFIG_TMPFS_POSIX_ACL
2365 	sb->s_xattr = shmem_xattr_handlers;
2366 	sb->s_flags |= MS_POSIXACL;
2367 #endif
2368 
2369 	inode = shmem_get_inode(sb, S_IFDIR | sbinfo->mode, 0, VM_NORESERVE);
2370 	if (!inode)
2371 		goto failed;
2372 	inode->i_uid = sbinfo->uid;
2373 	inode->i_gid = sbinfo->gid;
2374 	root = d_alloc_root(inode);
2375 	if (!root)
2376 		goto failed_iput;
2377 	sb->s_root = root;
2378 	return 0;
2379 
2380 failed_iput:
2381 	iput(inode);
2382 failed:
2383 	shmem_put_super(sb);
2384 	return err;
2385 }
2386 
2387 static struct kmem_cache *shmem_inode_cachep;
2388 
2389 static struct inode *shmem_alloc_inode(struct super_block *sb)
2390 {
2391 	struct shmem_inode_info *p;
2392 	p = (struct shmem_inode_info *)kmem_cache_alloc(shmem_inode_cachep, GFP_KERNEL);
2393 	if (!p)
2394 		return NULL;
2395 	return &p->vfs_inode;
2396 }
2397 
2398 static void shmem_destroy_inode(struct inode *inode)
2399 {
2400 	if ((inode->i_mode & S_IFMT) == S_IFREG) {
2401 		/* only struct inode is valid if it's an inline symlink */
2402 		mpol_free_shared_policy(&SHMEM_I(inode)->policy);
2403 	}
2404 	kmem_cache_free(shmem_inode_cachep, SHMEM_I(inode));
2405 }
2406 
2407 static void init_once(void *foo)
2408 {
2409 	struct shmem_inode_info *p = (struct shmem_inode_info *) foo;
2410 
2411 	inode_init_once(&p->vfs_inode);
2412 }
2413 
2414 static int init_inodecache(void)
2415 {
2416 	shmem_inode_cachep = kmem_cache_create("shmem_inode_cache",
2417 				sizeof(struct shmem_inode_info),
2418 				0, SLAB_PANIC, init_once);
2419 	return 0;
2420 }
2421 
2422 static void destroy_inodecache(void)
2423 {
2424 	kmem_cache_destroy(shmem_inode_cachep);
2425 }
2426 
2427 static const struct address_space_operations shmem_aops = {
2428 	.writepage	= shmem_writepage,
2429 	.set_page_dirty	= __set_page_dirty_no_writeback,
2430 #ifdef CONFIG_TMPFS
2431 	.readpage	= shmem_readpage,
2432 	.write_begin	= shmem_write_begin,
2433 	.write_end	= shmem_write_end,
2434 #endif
2435 	.migratepage	= migrate_page,
2436 	.error_remove_page = generic_error_remove_page,
2437 };
2438 
2439 static const struct file_operations shmem_file_operations = {
2440 	.mmap		= shmem_mmap,
2441 #ifdef CONFIG_TMPFS
2442 	.llseek		= generic_file_llseek,
2443 	.read		= do_sync_read,
2444 	.write		= do_sync_write,
2445 	.aio_read	= shmem_file_aio_read,
2446 	.aio_write	= generic_file_aio_write,
2447 	.fsync		= simple_sync_file,
2448 	.splice_read	= generic_file_splice_read,
2449 	.splice_write	= generic_file_splice_write,
2450 #endif
2451 };
2452 
2453 static const struct inode_operations shmem_inode_operations = {
2454 	.truncate	= shmem_truncate,
2455 	.setattr	= shmem_notify_change,
2456 	.truncate_range	= shmem_truncate_range,
2457 #ifdef CONFIG_TMPFS_POSIX_ACL
2458 	.setxattr	= generic_setxattr,
2459 	.getxattr	= generic_getxattr,
2460 	.listxattr	= generic_listxattr,
2461 	.removexattr	= generic_removexattr,
2462 	.check_acl	= generic_check_acl,
2463 #endif
2464 
2465 };
2466 
2467 static const struct inode_operations shmem_dir_inode_operations = {
2468 #ifdef CONFIG_TMPFS
2469 	.create		= shmem_create,
2470 	.lookup		= simple_lookup,
2471 	.link		= shmem_link,
2472 	.unlink		= shmem_unlink,
2473 	.symlink	= shmem_symlink,
2474 	.mkdir		= shmem_mkdir,
2475 	.rmdir		= shmem_rmdir,
2476 	.mknod		= shmem_mknod,
2477 	.rename		= shmem_rename,
2478 #endif
2479 #ifdef CONFIG_TMPFS_POSIX_ACL
2480 	.setattr	= shmem_notify_change,
2481 	.setxattr	= generic_setxattr,
2482 	.getxattr	= generic_getxattr,
2483 	.listxattr	= generic_listxattr,
2484 	.removexattr	= generic_removexattr,
2485 	.check_acl	= generic_check_acl,
2486 #endif
2487 };
2488 
2489 static const struct inode_operations shmem_special_inode_operations = {
2490 #ifdef CONFIG_TMPFS_POSIX_ACL
2491 	.setattr	= shmem_notify_change,
2492 	.setxattr	= generic_setxattr,
2493 	.getxattr	= generic_getxattr,
2494 	.listxattr	= generic_listxattr,
2495 	.removexattr	= generic_removexattr,
2496 	.check_acl	= generic_check_acl,
2497 #endif
2498 };
2499 
2500 static const struct super_operations shmem_ops = {
2501 	.alloc_inode	= shmem_alloc_inode,
2502 	.destroy_inode	= shmem_destroy_inode,
2503 #ifdef CONFIG_TMPFS
2504 	.statfs		= shmem_statfs,
2505 	.remount_fs	= shmem_remount_fs,
2506 	.show_options	= shmem_show_options,
2507 #endif
2508 	.delete_inode	= shmem_delete_inode,
2509 	.drop_inode	= generic_delete_inode,
2510 	.put_super	= shmem_put_super,
2511 };
2512 
2513 static const struct vm_operations_struct shmem_vm_ops = {
2514 	.fault		= shmem_fault,
2515 #ifdef CONFIG_NUMA
2516 	.set_policy     = shmem_set_policy,
2517 	.get_policy     = shmem_get_policy,
2518 #endif
2519 };
2520 
2521 
2522 static int shmem_get_sb(struct file_system_type *fs_type,
2523 	int flags, const char *dev_name, void *data, struct vfsmount *mnt)
2524 {
2525 	return get_sb_nodev(fs_type, flags, data, shmem_fill_super, mnt);
2526 }
2527 
2528 static struct file_system_type tmpfs_fs_type = {
2529 	.owner		= THIS_MODULE,
2530 	.name		= "tmpfs",
2531 	.get_sb		= shmem_get_sb,
2532 	.kill_sb	= kill_litter_super,
2533 };
2534 
2535 int __init init_tmpfs(void)
2536 {
2537 	int error;
2538 
2539 	error = bdi_init(&shmem_backing_dev_info);
2540 	if (error)
2541 		goto out4;
2542 
2543 	error = init_inodecache();
2544 	if (error)
2545 		goto out3;
2546 
2547 	error = register_filesystem(&tmpfs_fs_type);
2548 	if (error) {
2549 		printk(KERN_ERR "Could not register tmpfs\n");
2550 		goto out2;
2551 	}
2552 
2553 	shm_mnt = vfs_kern_mount(&tmpfs_fs_type, MS_NOUSER,
2554 				tmpfs_fs_type.name, NULL);
2555 	if (IS_ERR(shm_mnt)) {
2556 		error = PTR_ERR(shm_mnt);
2557 		printk(KERN_ERR "Could not kern_mount tmpfs\n");
2558 		goto out1;
2559 	}
2560 	return 0;
2561 
2562 out1:
2563 	unregister_filesystem(&tmpfs_fs_type);
2564 out2:
2565 	destroy_inodecache();
2566 out3:
2567 	bdi_destroy(&shmem_backing_dev_info);
2568 out4:
2569 	shm_mnt = ERR_PTR(error);
2570 	return error;
2571 }
2572 
2573 #else /* !CONFIG_SHMEM */
2574 
2575 /*
2576  * tiny-shmem: simple shmemfs and tmpfs using ramfs code
2577  *
2578  * This is intended for small system where the benefits of the full
2579  * shmem code (swap-backed and resource-limited) are outweighed by
2580  * their complexity. On systems without swap this code should be
2581  * effectively equivalent, but much lighter weight.
2582  */
2583 
2584 #include <linux/ramfs.h>
2585 
2586 static struct file_system_type tmpfs_fs_type = {
2587 	.name		= "tmpfs",
2588 	.get_sb		= ramfs_get_sb,
2589 	.kill_sb	= kill_litter_super,
2590 };
2591 
2592 int __init init_tmpfs(void)
2593 {
2594 	BUG_ON(register_filesystem(&tmpfs_fs_type) != 0);
2595 
2596 	shm_mnt = kern_mount(&tmpfs_fs_type);
2597 	BUG_ON(IS_ERR(shm_mnt));
2598 
2599 	return 0;
2600 }
2601 
2602 int shmem_unuse(swp_entry_t entry, struct page *page)
2603 {
2604 	return 0;
2605 }
2606 
2607 int shmem_lock(struct file *file, int lock, struct user_struct *user)
2608 {
2609 	return 0;
2610 }
2611 
2612 #define shmem_vm_ops				generic_file_vm_ops
2613 #define shmem_file_operations			ramfs_file_operations
2614 #define shmem_get_inode(sb, mode, dev, flags)	ramfs_get_inode(sb, mode, dev)
2615 #define shmem_acct_size(flags, size)		0
2616 #define shmem_unacct_size(flags, size)		do {} while (0)
2617 #define SHMEM_MAX_BYTES				MAX_LFS_FILESIZE
2618 
2619 #endif /* CONFIG_SHMEM */
2620 
2621 /* common code */
2622 
2623 /**
2624  * shmem_file_setup - get an unlinked file living in tmpfs
2625  * @name: name for dentry (to be seen in /proc/<pid>/maps
2626  * @size: size to be set for the file
2627  * @flags: VM_NORESERVE suppresses pre-accounting of the entire object size
2628  */
2629 struct file *shmem_file_setup(const char *name, loff_t size, unsigned long flags)
2630 {
2631 	int error;
2632 	struct file *file;
2633 	struct inode *inode;
2634 	struct path path;
2635 	struct dentry *root;
2636 	struct qstr this;
2637 
2638 	if (IS_ERR(shm_mnt))
2639 		return (void *)shm_mnt;
2640 
2641 	if (size < 0 || size > SHMEM_MAX_BYTES)
2642 		return ERR_PTR(-EINVAL);
2643 
2644 	if (shmem_acct_size(flags, size))
2645 		return ERR_PTR(-ENOMEM);
2646 
2647 	error = -ENOMEM;
2648 	this.name = name;
2649 	this.len = strlen(name);
2650 	this.hash = 0; /* will go */
2651 	root = shm_mnt->mnt_root;
2652 	path.dentry = d_alloc(root, &this);
2653 	if (!path.dentry)
2654 		goto put_memory;
2655 	path.mnt = mntget(shm_mnt);
2656 
2657 	error = -ENOSPC;
2658 	inode = shmem_get_inode(root->d_sb, S_IFREG | S_IRWXUGO, 0, flags);
2659 	if (!inode)
2660 		goto put_dentry;
2661 
2662 	d_instantiate(path.dentry, inode);
2663 	inode->i_size = size;
2664 	inode->i_nlink = 0;	/* It is unlinked */
2665 #ifndef CONFIG_MMU
2666 	error = ramfs_nommu_expand_for_mapping(inode, size);
2667 	if (error)
2668 		goto put_dentry;
2669 #endif
2670 
2671 	error = -ENFILE;
2672 	file = alloc_file(&path, FMODE_WRITE | FMODE_READ,
2673 		  &shmem_file_operations);
2674 	if (!file)
2675 		goto put_dentry;
2676 
2677 	return file;
2678 
2679 put_dentry:
2680 	path_put(&path);
2681 put_memory:
2682 	shmem_unacct_size(flags, size);
2683 	return ERR_PTR(error);
2684 }
2685 EXPORT_SYMBOL_GPL(shmem_file_setup);
2686 
2687 /**
2688  * shmem_zero_setup - setup a shared anonymous mapping
2689  * @vma: the vma to be mmapped is prepared by do_mmap_pgoff
2690  */
2691 int shmem_zero_setup(struct vm_area_struct *vma)
2692 {
2693 	struct file *file;
2694 	loff_t size = vma->vm_end - vma->vm_start;
2695 
2696 	file = shmem_file_setup("dev/zero", size, vma->vm_flags);
2697 	if (IS_ERR(file))
2698 		return PTR_ERR(file);
2699 
2700 	if (vma->vm_file)
2701 		fput(vma->vm_file);
2702 	vma->vm_file = file;
2703 	vma->vm_ops = &shmem_vm_ops;
2704 	return 0;
2705 }
2706