file.c revision 8b0e330b7720a206339887044fa275bf537a5264 
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/fs.h>
10#include <linux/mm.h>
11#include <linux/time.h>
12#include <linux/slab.h>
13#include <linux/vmalloc.h>
14#include <linux/file.h>
15#include <linux/bitops.h>
16#include <linux/interrupt.h>
17#include <linux/spinlock.h>
18#include <linux/rcupdate.h>
19#include <linux/workqueue.h>
20
21struct fdtable_defer {
22	spinlock_t lock;
23	struct work_struct wq;
24	struct timer_list timer;
25	struct fdtable *next;
26};
27
28/*
29 * We use this list to defer free fdtables that have vmalloced
30 * sets/arrays. By keeping a per-cpu list, we avoid having to embed
31 * the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
32 * this per-task structure.
33 */
34static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
35
36
37/*
38 * Allocate an fd array, using kmalloc or vmalloc.
39 * Note: the array isn't cleared at allocation time.
40 */
41struct file ** alloc_fd_array(int num)
42{
43	struct file **new_fds;
44	int size = num * sizeof(struct file *);
45
46	if (size <= PAGE_SIZE)
47		new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
48	else
49		new_fds = (struct file **) vmalloc(size);
50	return new_fds;
51}
52
53void free_fd_array(struct file **array, int num)
54{
55	int size = num * sizeof(struct file *);
56
57	if (!array) {
58		printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
59		return;
60	}
61
62	if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
63		return;
64	else if (size <= PAGE_SIZE)
65		kfree(array);
66	else
67		vfree(array);
68}
69
70static void __free_fdtable(struct fdtable *fdt)
71{
72	free_fdset(fdt->open_fds, fdt->max_fdset);
73	free_fdset(fdt->close_on_exec, fdt->max_fdset);
74	free_fd_array(fdt->fd, fdt->max_fds);
75	kfree(fdt);
76}
77
78static void fdtable_timer(unsigned long data)
79{
80	struct fdtable_defer *fddef = (struct fdtable_defer *)data;
81
82	spin_lock(&fddef->lock);
83	/*
84	 * If someone already emptied the queue return.
85	 */
86	if (!fddef->next)
87		goto out;
88	if (!schedule_work(&fddef->wq))
89		mod_timer(&fddef->timer, 5);
90out:
91	spin_unlock(&fddef->lock);
92}
93
94static void free_fdtable_work(struct fdtable_defer *f)
95{
96	struct fdtable *fdt;
97
98	spin_lock_bh(&f->lock);
99	fdt = f->next;
100	f->next = NULL;
101	spin_unlock_bh(&f->lock);
102	while(fdt) {
103		struct fdtable *next = fdt->next;
104		__free_fdtable(fdt);
105		fdt = next;
106	}
107}
108
109static void free_fdtable_rcu(struct rcu_head *rcu)
110{
111	struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
112	int fdset_size, fdarray_size;
113	struct fdtable_defer *fddef;
114
115	BUG_ON(!fdt);
116	fdset_size = fdt->max_fdset / 8;
117	fdarray_size = fdt->max_fds * sizeof(struct file *);
118
119	if (fdt->free_files) {
120		/*
121		 * The this fdtable was embedded in the files structure
122		 * and the files structure itself was getting destroyed.
123		 * It is now safe to free the files structure.
124		 */
125		kmem_cache_free(files_cachep, fdt->free_files);
126		return;
127	}
128	if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
129		fdt->max_fds <= NR_OPEN_DEFAULT) {
130		/*
131		 * The fdtable was embedded
132		 */
133		return;
134	}
135	if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
136		kfree(fdt->open_fds);
137		kfree(fdt->close_on_exec);
138		kfree(fdt->fd);
139		kfree(fdt);
140	} else {
141		fddef = &get_cpu_var(fdtable_defer_list);
142		spin_lock(&fddef->lock);
143		fdt->next = fddef->next;
144		fddef->next = fdt;
145		/*
146		 * vmallocs are handled from the workqueue context.
147		 * If the per-cpu workqueue is running, then we
148		 * defer work scheduling through a timer.
149		 */
150		if (!schedule_work(&fddef->wq))
151			mod_timer(&fddef->timer, 5);
152		spin_unlock(&fddef->lock);
153		put_cpu_var(fdtable_defer_list);
154	}
155}
156
157void free_fdtable(struct fdtable *fdt)
158{
159	if (fdt->free_files ||
160		fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
161		fdt->max_fds > NR_OPEN_DEFAULT)
162		call_rcu(&fdt->rcu, free_fdtable_rcu);
163}
164
165/*
166 * Expand the fdset in the files_struct.  Called with the files spinlock
167 * held for write.
168 */
169static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
170{
171	int i;
172	int count;
173
174	BUG_ON(nfdt->max_fdset < fdt->max_fdset);
175	BUG_ON(nfdt->max_fds < fdt->max_fds);
176	/* Copy the existing tables and install the new pointers */
177
178	i = fdt->max_fdset / (sizeof(unsigned long) * 8);
179	count = (nfdt->max_fdset - fdt->max_fdset) / 8;
180
181	/*
182	 * Don't copy the entire array if the current fdset is
183	 * not yet initialised.
184	 */
185	if (i) {
186		memcpy (nfdt->open_fds, fdt->open_fds,
187						fdt->max_fdset/8);
188		memcpy (nfdt->close_on_exec, fdt->close_on_exec,
189						fdt->max_fdset/8);
190		memset (&nfdt->open_fds->fds_bits[i], 0, count);
191		memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
192	}
193
194	/* Don't copy/clear the array if we are creating a new
195	   fd array for fork() */
196	if (fdt->max_fds) {
197		memcpy(nfdt->fd, fdt->fd,
198			fdt->max_fds * sizeof(struct file *));
199		/* clear the remainder of the array */
200		memset(&nfdt->fd[fdt->max_fds], 0,
201		       (nfdt->max_fds - fdt->max_fds) *
202					sizeof(struct file *));
203	}
204}
205
206/*
207 * Allocate an fdset array, using kmalloc or vmalloc.
208 * Note: the array isn't cleared at allocation time.
209 */
210fd_set * alloc_fdset(int num)
211{
212	fd_set *new_fdset;
213	int size = num / 8;
214
215	if (size <= PAGE_SIZE)
216		new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
217	else
218		new_fdset = (fd_set *) vmalloc(size);
219	return new_fdset;
220}
221
222void free_fdset(fd_set *array, int num)
223{
224	if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
225		return;
226	else if (num <= 8 * PAGE_SIZE)
227		kfree(array);
228	else
229		vfree(array);
230}
231
232static struct fdtable *alloc_fdtable(int nr)
233{
234	struct fdtable *fdt = NULL;
235	int nfds = 0;
236  	fd_set *new_openset = NULL, *new_execset = NULL;
237	struct file **new_fds;
238
239	fdt = kzalloc(sizeof(*fdt), GFP_KERNEL);
240	if (!fdt)
241  		goto out;
242
243	nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1));
244	if (nfds > NR_OPEN)
245		nfds = NR_OPEN;
246
247  	new_openset = alloc_fdset(nfds);
248  	new_execset = alloc_fdset(nfds);
249  	if (!new_openset || !new_execset)
250  		goto out;
251	fdt->open_fds = new_openset;
252	fdt->close_on_exec = new_execset;
253	fdt->max_fdset = nfds;
254
255	nfds = NR_OPEN_DEFAULT;
256	/*
257	 * Expand to the max in easy steps, and keep expanding it until
258	 * we have enough for the requested fd array size.
259	 */
260	do {
261#if NR_OPEN_DEFAULT < 256
262		if (nfds < 256)
263			nfds = 256;
264		else
265#endif
266		if (nfds < (PAGE_SIZE / sizeof(struct file *)))
267			nfds = PAGE_SIZE / sizeof(struct file *);
268		else {
269			nfds = nfds * 2;
270			if (nfds > NR_OPEN)
271				nfds = NR_OPEN;
272  		}
273	} while (nfds <= nr);
274	new_fds = alloc_fd_array(nfds);
275	if (!new_fds)
276		goto out2;
277	fdt->fd = new_fds;
278	fdt->max_fds = nfds;
279	fdt->free_files = NULL;
280	return fdt;
281out2:
282	nfds = fdt->max_fdset;
283out:
284	free_fdset(new_openset, nfds);
285	free_fdset(new_execset, nfds);
286	kfree(fdt);
287	return NULL;
288}
289
290/*
291 * Expands the file descriptor table - it will allocate a new fdtable and
292 * both fd array and fdset. It is expected to be called with the
293 * files_lock held.
294 */
295static int expand_fdtable(struct files_struct *files, int nr)
296	__releases(files->file_lock)
297	__acquires(files->file_lock)
298{
299	int error = 0;
300	struct fdtable *fdt;
301	struct fdtable *nfdt = NULL;
302
303	spin_unlock(&files->file_lock);
304	nfdt = alloc_fdtable(nr);
305	if (!nfdt) {
306		error = -ENOMEM;
307		spin_lock(&files->file_lock);
308		goto out;
309	}
310
311	spin_lock(&files->file_lock);
312	fdt = files_fdtable(files);
313	/*
314	 * Check again since another task may have expanded the
315	 * fd table while we dropped the lock
316	 */
317	if (nr >= fdt->max_fds || nr >= fdt->max_fdset) {
318		copy_fdtable(nfdt, fdt);
319	} else {
320		/* Somebody expanded while we dropped file_lock */
321		spin_unlock(&files->file_lock);
322		__free_fdtable(nfdt);
323		spin_lock(&files->file_lock);
324		goto out;
325	}
326	rcu_assign_pointer(files->fdt, nfdt);
327	free_fdtable(fdt);
328out:
329	return error;
330}
331
332/*
333 * Expand files.
334 * Return <0 on error; 0 nothing done; 1 files expanded, we may have blocked.
335 * Should be called with the files->file_lock spinlock held for write.
336 */
337int expand_files(struct files_struct *files, int nr)
338{
339	int err, expand = 0;
340	struct fdtable *fdt;
341
342	fdt = files_fdtable(files);
343	if (nr >= fdt->max_fdset || nr >= fdt->max_fds) {
344		if (fdt->max_fdset >= NR_OPEN ||
345			fdt->max_fds >= NR_OPEN || nr >= NR_OPEN) {
346			err = -EMFILE;
347			goto out;
348		}
349		expand = 1;
350		if ((err = expand_fdtable(files, nr)))
351			goto out;
352	}
353	err = expand;
354out:
355	return err;
356}
357
358static void __devinit fdtable_defer_list_init(int cpu)
359{
360	struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
361	spin_lock_init(&fddef->lock);
362	INIT_WORK(&fddef->wq, (void (*)(void *))free_fdtable_work, fddef);
363	init_timer(&fddef->timer);
364	fddef->timer.data = (unsigned long)fddef;
365	fddef->timer.function = fdtable_timer;
366	fddef->next = NULL;
367}
368
369void __init files_defer_init(void)
370{
371	int i;
372	for_each_possible_cpu(i)
373		fdtable_defer_list_init(i);
374}
375