Root/fs/file.c

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    if (size <= PAGE_SIZE)
45        return kmalloc(size, GFP_KERNEL);
46    else
47        return vmalloc(size);
48}
49
50static 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
58static 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
66static 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
85void 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 */
121static 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
140static 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
186out_arr:
187    free_fdarr(fdt);
188out_fdt:
189    kfree(fdt);
190out:
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 */
201static 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 */
250int 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
275static 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 */
294struct 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
402out_release:
403    kmem_cache_free(files_cachep, newf);
404out:
405    return NULL;
406}
407
408static 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
416void __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
425struct 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 */
441int 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);
449repeat:
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
487out:
488    spin_unlock(&files->file_lock);
489    return error;
490}
491
492int get_unused_fd(void)
493{
494    return alloc_fd(0, 0);
495}
496EXPORT_SYMBOL(get_unused_fd);
497

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