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1 | /* | |
2 | * linux/fs/file.c | |
3 | * | |
4 | * Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes | |
5 | * | |
6 | * Manage the dynamic fd arrays in the process files_struct. | |
7 | */ | |
8 | ||
9 | #include <linux/module.h> | |
10 | #include <linux/fs.h> | |
11 | #include <linux/mm.h> | |
12 | #include <linux/time.h> | |
13 | #include <linux/sched.h> | |
14 | #include <linux/slab.h> | |
15 | #include <linux/vmalloc.h> | |
16 | #include <linux/file.h> | |
17 | #include <linux/fdtable.h> | |
18 | #include <linux/bitops.h> | |
19 | #include <linux/interrupt.h> | |
20 | #include <linux/spinlock.h> | |
21 | #include <linux/rcupdate.h> | |
22 | #include <linux/workqueue.h> | |
23 | ||
24 | struct fdtable_defer { | |
25 | spinlock_t lock; | |
26 | struct work_struct wq; | |
27 | struct fdtable *next; | |
28 | }; | |
29 | ||
30 | int sysctl_nr_open __read_mostly = 1024*1024; | |
31 | int sysctl_nr_open_min = BITS_PER_LONG; | |
32 | int sysctl_nr_open_max = 1024 * 1024; /* raised later */ | |
33 | ||
34 | /* | |
35 | * We use this list to defer free fdtables that have vmalloced | |
36 | * sets/arrays. By keeping a per-cpu list, we avoid having to embed | |
37 | * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in | |
38 | * this per-task structure. | |
39 | */ | |
40 | static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list); | |
41 | ||
42 | static inline void * alloc_fdmem(unsigned int size) | |
43 | { | |
44 | if (size <= PAGE_SIZE) | |
45 | return kmalloc(size, GFP_KERNEL); | |
46 | else | |
47 | return vmalloc(size); | |
48 | } | |
49 | ||
50 | static inline void free_fdarr(struct fdtable *fdt) | |
51 | { | |
52 | if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) | |
53 | kfree(fdt->fd); | |
54 | else | |
55 | vfree(fdt->fd); | |
56 | } | |
57 | ||
58 | static inline void free_fdset(struct fdtable *fdt) | |
59 | { | |
60 | if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2)) | |
61 | kfree(fdt->open_fds); | |
62 | else | |
63 | vfree(fdt->open_fds); | |
64 | } | |
65 | ||
66 | static void free_fdtable_work(struct work_struct *work) | |
67 | { | |
68 | struct fdtable_defer *f = | |
69 | container_of(work, struct fdtable_defer, wq); | |
70 | struct fdtable *fdt; | |
71 | ||
72 | spin_lock_bh(&f->lock); | |
73 | fdt = f->next; | |
74 | f->next = NULL; | |
75 | spin_unlock_bh(&f->lock); | |
76 | while(fdt) { | |
77 | struct fdtable *next = fdt->next; | |
78 | vfree(fdt->fd); | |
79 | free_fdset(fdt); | |
80 | kfree(fdt); | |
81 | fdt = next; | |
82 | } | |
83 | } | |
84 | ||
85 | void free_fdtable_rcu(struct rcu_head *rcu) | |
86 | { | |
87 | struct fdtable *fdt = container_of(rcu, struct fdtable, rcu); | |
88 | struct fdtable_defer *fddef; | |
89 | ||
90 | BUG_ON(!fdt); | |
91 | ||
92 | if (fdt->max_fds <= NR_OPEN_DEFAULT) { | |
93 | /* | |
94 | * This fdtable is embedded in the files structure and that | |
95 | * structure itself is getting destroyed. | |
96 | */ | |
97 | kmem_cache_free(files_cachep, | |
98 | container_of(fdt, struct files_struct, fdtab)); | |
99 | return; | |
100 | } | |
101 | if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) { | |
102 | kfree(fdt->fd); | |
103 | kfree(fdt->open_fds); | |
104 | kfree(fdt); | |
105 | } else { | |
106 | fddef = &get_cpu_var(fdtable_defer_list); | |
107 | spin_lock(&fddef->lock); | |
108 | fdt->next = fddef->next; | |
109 | fddef->next = fdt; | |
110 | /* vmallocs are handled from the workqueue context */ | |
111 | schedule_work(&fddef->wq); | |
112 | spin_unlock(&fddef->lock); | |
113 | put_cpu_var(fdtable_defer_list); | |
114 | } | |
115 | } | |
116 | ||
117 | /* | |
118 | * Expand the fdset in the files_struct. Called with the files spinlock | |
119 | * held for write. | |
120 | */ | |
121 | static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt) | |
122 | { | |
123 | unsigned int cpy, set; | |
124 | ||
125 | BUG_ON(nfdt->max_fds < ofdt->max_fds); | |
126 | ||
127 | cpy = ofdt->max_fds * sizeof(struct file *); | |
128 | set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *); | |
129 | memcpy(nfdt->fd, ofdt->fd, cpy); | |
130 | memset((char *)(nfdt->fd) + cpy, 0, set); | |
131 | ||
132 | cpy = ofdt->max_fds / BITS_PER_BYTE; | |
133 | set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE; | |
134 | memcpy(nfdt->open_fds, ofdt->open_fds, cpy); | |
135 | memset((char *)(nfdt->open_fds) + cpy, 0, set); | |
136 | memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy); | |
137 | memset((char *)(nfdt->close_on_exec) + cpy, 0, set); | |
138 | } | |
139 | ||
140 | static struct fdtable * alloc_fdtable(unsigned int nr) | |
141 | { | |
142 | struct fdtable *fdt; | |
143 | char *data; | |
144 | ||
145 | /* | |
146 | * Figure out how many fds we actually want to support in this fdtable. | |
147 | * Allocation steps are keyed to the size of the fdarray, since it | |
148 | * grows far faster than any of the other dynamic data. We try to fit | |
149 | * the fdarray into comfortable page-tuned chunks: starting at 1024B | |
150 | * and growing in powers of two from there on. | |
151 | */ | |
152 | nr /= (1024 / sizeof(struct file *)); | |
153 | nr = roundup_pow_of_two(nr + 1); | |
154 | nr *= (1024 / sizeof(struct file *)); | |
155 | /* | |
156 | * Note that this can drive nr *below* what we had passed if sysctl_nr_open | |
157 | * had been set lower between the check in expand_files() and here. Deal | |
158 | * with that in caller, it's cheaper that way. | |
159 | * | |
160 | * We make sure that nr remains a multiple of BITS_PER_LONG - otherwise | |
161 | * bitmaps handling below becomes unpleasant, to put it mildly... | |
162 | */ | |
163 | if (unlikely(nr > sysctl_nr_open)) | |
164 | nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1; | |
165 | ||
166 | fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL); | |
167 | if (!fdt) | |
168 | goto out; | |
169 | fdt->max_fds = nr; | |
170 | data = alloc_fdmem(nr * sizeof(struct file *)); | |
171 | if (!data) | |
172 | goto out_fdt; | |
173 | fdt->fd = (struct file **)data; | |
174 | data = alloc_fdmem(max_t(unsigned int, | |
175 | 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES)); | |
176 | if (!data) | |
177 | goto out_arr; | |
178 | fdt->open_fds = (fd_set *)data; | |
179 | data += nr / BITS_PER_BYTE; | |
180 | fdt->close_on_exec = (fd_set *)data; | |
181 | INIT_RCU_HEAD(&fdt->rcu); | |
182 | fdt->next = NULL; | |
183 | ||
184 | return fdt; | |
185 | ||
186 | out_arr: | |
187 | free_fdarr(fdt); | |
188 | out_fdt: | |
189 | kfree(fdt); | |
190 | out: | |
191 | return NULL; | |
192 | } | |
193 | ||
194 | /* | |
195 | * Expand the file descriptor table. | |
196 | * This function will allocate a new fdtable and both fd array and fdset, of | |
197 | * the given size. | |
198 | * Return <0 error code on error; 1 on successful completion. | |
199 | * The files->file_lock should be held on entry, and will be held on exit. | |
200 | */ | |
201 | static int expand_fdtable(struct files_struct *files, int nr) | |
202 | __releases(files->file_lock) | |
203 | __acquires(files->file_lock) | |
204 | { | |
205 | struct fdtable *new_fdt, *cur_fdt; | |
206 | ||
207 | spin_unlock(&files->file_lock); | |
208 | new_fdt = alloc_fdtable(nr); | |
209 | spin_lock(&files->file_lock); | |
210 | if (!new_fdt) | |
211 | return -ENOMEM; | |
212 | /* | |
213 | * extremely unlikely race - sysctl_nr_open decreased between the check in | |
214 | * caller and alloc_fdtable(). Cheaper to catch it here... | |
215 | */ | |
216 | if (unlikely(new_fdt->max_fds <= nr)) { | |
217 | free_fdarr(new_fdt); | |
218 | free_fdset(new_fdt); | |
219 | kfree(new_fdt); | |
220 | return -EMFILE; | |
221 | } | |
222 | /* | |
223 | * Check again since another task may have expanded the fd table while | |
224 | * we dropped the lock | |
225 | */ | |
226 | cur_fdt = files_fdtable(files); | |
227 | if (nr >= cur_fdt->max_fds) { | |
228 | /* Continue as planned */ | |
229 | copy_fdtable(new_fdt, cur_fdt); | |
230 | rcu_assign_pointer(files->fdt, new_fdt); | |
231 | if (cur_fdt->max_fds > NR_OPEN_DEFAULT) | |
232 | free_fdtable(cur_fdt); | |
233 | } else { | |
234 | /* Somebody else expanded, so undo our attempt */ | |
235 | free_fdarr(new_fdt); | |
236 | free_fdset(new_fdt); | |
237 | kfree(new_fdt); | |
238 | } | |
239 | return 1; | |
240 | } | |
241 | ||
242 | /* | |
243 | * Expand files. | |
244 | * This function will expand the file structures, if the requested size exceeds | |
245 | * the current capacity and there is room for expansion. | |
246 | * Return <0 error code on error; 0 when nothing done; 1 when files were | |
247 | * expanded and execution may have blocked. | |
248 | * The files->file_lock should be held on entry, and will be held on exit. | |
249 | */ | |
250 | int expand_files(struct files_struct *files, int nr) | |
251 | { | |
252 | struct fdtable *fdt; | |
253 | ||
254 | fdt = files_fdtable(files); | |
255 | ||
256 | /* | |
257 | * N.B. For clone tasks sharing a files structure, this test | |
258 | * will limit the total number of files that can be opened. | |
259 | */ | |
260 | if (nr >= rlimit(RLIMIT_NOFILE)) | |
261 | return -EMFILE; | |
262 | ||
263 | /* Do we need to expand? */ | |
264 | if (nr < fdt->max_fds) | |
265 | return 0; | |
266 | ||
267 | /* Can we expand? */ | |
268 | if (nr >= sysctl_nr_open) | |
269 | return -EMFILE; | |
270 | ||
271 | /* All good, so we try */ | |
272 | return expand_fdtable(files, nr); | |
273 | } | |
274 | ||
275 | static int count_open_files(struct fdtable *fdt) | |
276 | { | |
277 | int size = fdt->max_fds; | |
278 | int i; | |
279 | ||
280 | /* Find the last open fd */ | |
281 | for (i = size/(8*sizeof(long)); i > 0; ) { | |
282 | if (fdt->open_fds->fds_bits[--i]) | |
283 | break; | |
284 | } | |
285 | i = (i+1) * 8 * sizeof(long); | |
286 | return i; | |
287 | } | |
288 | ||
289 | /* | |
290 | * Allocate a new files structure and copy contents from the | |
291 | * passed in files structure. | |
292 | * errorp will be valid only when the returned files_struct is NULL. | |
293 | */ | |
294 | struct files_struct *dup_fd(struct files_struct *oldf, int *errorp) | |
295 | { | |
296 | struct files_struct *newf; | |
297 | struct file **old_fds, **new_fds; | |
298 | int open_files, size, i; | |
299 | struct fdtable *old_fdt, *new_fdt; | |
300 | ||
301 | *errorp = -ENOMEM; | |
302 | newf = kmem_cache_alloc(files_cachep, GFP_KERNEL); | |
303 | if (!newf) | |
304 | goto out; | |
305 | ||
306 | atomic_set(&newf->count, 1); | |
307 | ||
308 | spin_lock_init(&newf->file_lock); | |
309 | newf->next_fd = 0; | |
310 | new_fdt = &newf->fdtab; | |
311 | new_fdt->max_fds = NR_OPEN_DEFAULT; | |
312 | new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init; | |
313 | new_fdt->open_fds = (fd_set *)&newf->open_fds_init; | |
314 | new_fdt->fd = &newf->fd_array[0]; | |
315 | INIT_RCU_HEAD(&new_fdt->rcu); | |
316 | new_fdt->next = NULL; | |
317 | ||
318 | spin_lock(&oldf->file_lock); | |
319 | old_fdt = files_fdtable(oldf); | |
320 | open_files = count_open_files(old_fdt); | |
321 | ||
322 | /* | |
323 | * Check whether we need to allocate a larger fd array and fd set. | |
324 | */ | |
325 | while (unlikely(open_files > new_fdt->max_fds)) { | |
326 | spin_unlock(&oldf->file_lock); | |
327 | ||
328 | if (new_fdt != &newf->fdtab) { | |
329 | free_fdarr(new_fdt); | |
330 | free_fdset(new_fdt); | |
331 | kfree(new_fdt); | |
332 | } | |
333 | ||
334 | new_fdt = alloc_fdtable(open_files - 1); | |
335 | if (!new_fdt) { | |
336 | *errorp = -ENOMEM; | |
337 | goto out_release; | |
338 | } | |
339 | ||
340 | /* beyond sysctl_nr_open; nothing to do */ | |
341 | if (unlikely(new_fdt->max_fds < open_files)) { | |
342 | free_fdarr(new_fdt); | |
343 | free_fdset(new_fdt); | |
344 | kfree(new_fdt); | |
345 | *errorp = -EMFILE; | |
346 | goto out_release; | |
347 | } | |
348 | ||
349 | /* | |
350 | * Reacquire the oldf lock and a pointer to its fd table | |
351 | * who knows it may have a new bigger fd table. We need | |
352 | * the latest pointer. | |
353 | */ | |
354 | spin_lock(&oldf->file_lock); | |
355 | old_fdt = files_fdtable(oldf); | |
356 | open_files = count_open_files(old_fdt); | |
357 | } | |
358 | ||
359 | old_fds = old_fdt->fd; | |
360 | new_fds = new_fdt->fd; | |
361 | ||
362 | memcpy(new_fdt->open_fds->fds_bits, | |
363 | old_fdt->open_fds->fds_bits, open_files/8); | |
364 | memcpy(new_fdt->close_on_exec->fds_bits, | |
365 | old_fdt->close_on_exec->fds_bits, open_files/8); | |
366 | ||
367 | for (i = open_files; i != 0; i--) { | |
368 | struct file *f = *old_fds++; | |
369 | if (f) { | |
370 | get_file(f); | |
371 | } else { | |
372 | /* | |
373 | * The fd may be claimed in the fd bitmap but not yet | |
374 | * instantiated in the files array if a sibling thread | |
375 | * is partway through open(). So make sure that this | |
376 | * fd is available to the new process. | |
377 | */ | |
378 | FD_CLR(open_files - i, new_fdt->open_fds); | |
379 | } | |
380 | rcu_assign_pointer(*new_fds++, f); | |
381 | } | |
382 | spin_unlock(&oldf->file_lock); | |
383 | ||
384 | /* compute the remainder to be cleared */ | |
385 | size = (new_fdt->max_fds - open_files) * sizeof(struct file *); | |
386 | ||
387 | /* This is long word aligned thus could use a optimized version */ | |
388 | memset(new_fds, 0, size); | |
389 | ||
390 | if (new_fdt->max_fds > open_files) { | |
391 | int left = (new_fdt->max_fds-open_files)/8; | |
392 | int start = open_files / (8 * sizeof(unsigned long)); | |
393 | ||
394 | memset(&new_fdt->open_fds->fds_bits[start], 0, left); | |
395 | memset(&new_fdt->close_on_exec->fds_bits[start], 0, left); | |
396 | } | |
397 | ||
398 | rcu_assign_pointer(newf->fdt, new_fdt); | |
399 | ||
400 | return newf; | |
401 | ||
402 | out_release: | |
403 | kmem_cache_free(files_cachep, newf); | |
404 | out: | |
405 | return NULL; | |
406 | } | |
407 | ||
408 | static void __devinit fdtable_defer_list_init(int cpu) | |
409 | { | |
410 | struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu); | |
411 | spin_lock_init(&fddef->lock); | |
412 | INIT_WORK(&fddef->wq, free_fdtable_work); | |
413 | fddef->next = NULL; | |
414 | } | |
415 | ||
416 | void __init files_defer_init(void) | |
417 | { | |
418 | int i; | |
419 | for_each_possible_cpu(i) | |
420 | fdtable_defer_list_init(i); | |
421 | sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) & | |
422 | -BITS_PER_LONG; | |
423 | } | |
424 | ||
425 | struct files_struct init_files = { | |
426 | .count = ATOMIC_INIT(1), | |
427 | .fdt = &init_files.fdtab, | |
428 | .fdtab = { | |
429 | .max_fds = NR_OPEN_DEFAULT, | |
430 | .fd = &init_files.fd_array[0], | |
431 | .close_on_exec = (fd_set *)&init_files.close_on_exec_init, | |
432 | .open_fds = (fd_set *)&init_files.open_fds_init, | |
433 | .rcu = RCU_HEAD_INIT, | |
434 | }, | |
435 | .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock), | |
436 | }; | |
437 | ||
438 | /* | |
439 | * allocate a file descriptor, mark it busy. | |
440 | */ | |
441 | int alloc_fd(unsigned start, unsigned flags) | |
442 | { | |
443 | struct files_struct *files = current->files; | |
444 | unsigned int fd; | |
445 | int error; | |
446 | struct fdtable *fdt; | |
447 | ||
448 | spin_lock(&files->file_lock); | |
449 | repeat: | |
450 | fdt = files_fdtable(files); | |
451 | fd = start; | |
452 | if (fd < files->next_fd) | |
453 | fd = files->next_fd; | |
454 | ||
455 | if (fd < fdt->max_fds) | |
456 | fd = find_next_zero_bit(fdt->open_fds->fds_bits, | |
457 | fdt->max_fds, fd); | |
458 | ||
459 | error = expand_files(files, fd); | |
460 | if (error < 0) | |
461 | goto out; | |
462 | ||
463 | /* | |
464 | * If we needed to expand the fs array we | |
465 | * might have blocked - try again. | |
466 | */ | |
467 | if (error) | |
468 | goto repeat; | |
469 | ||
470 | if (start <= files->next_fd) | |
471 | files->next_fd = fd + 1; | |
472 | ||
473 | FD_SET(fd, fdt->open_fds); | |
474 | if (flags & O_CLOEXEC) | |
475 | FD_SET(fd, fdt->close_on_exec); | |
476 | else | |
477 | FD_CLR(fd, fdt->close_on_exec); | |
478 | error = fd; | |
479 | #if 1 | |
480 | /* Sanity check */ | |
481 | if (rcu_dereference_raw(fdt->fd[fd]) != NULL) { | |
482 | printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd); | |
483 | rcu_assign_pointer(fdt->fd[fd], NULL); | |
484 | } | |
485 | #endif | |
486 | ||
487 | out: | |
488 | spin_unlock(&files->file_lock); | |
489 | return error; | |
490 | } | |
491 | ||
492 | int get_unused_fd(void) | |
493 | { | |
494 | return alloc_fd(0, 0); | |
495 | } | |
496 | EXPORT_SYMBOL(get_unused_fd); |