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