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