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/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
25struct fdtable_defer {
26    spinlock_t lock;
27    struct work_struct wq;
28    struct fdtable *next;
29};
30
31int sysctl_nr_open __read_mostly = 1024*1024;
32int sysctl_nr_open_min = BITS_PER_LONG;
33int 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 */
41static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
42
43static void *alloc_fdmem(unsigned int 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
57static void free_fdmem(void *ptr)
58{
59    is_vmalloc_addr(ptr) ? vfree(ptr) : kfree(ptr);
60}
61
62static void __free_fdtable(struct fdtable *fdt)
63{
64    free_fdmem(fdt->fd);
65    free_fdmem(fdt->open_fds);
66    kfree(fdt);
67}
68
69static 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
87void 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 */
123static 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
142static struct fdtable * alloc_fdtable(unsigned int nr)
143{
144    struct fdtable *fdt;
145    char *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 = (struct file **)data;
176    data = alloc_fdmem(max_t(unsigned int,
177                 2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
178    if (!data)
179        goto out_arr;
180    fdt->open_fds = (fd_set *)data;
181    data += nr / BITS_PER_BYTE;
182    fdt->close_on_exec = (fd_set *)data;
183    fdt->next = NULL;
184
185    return fdt;
186
187out_arr:
188    free_fdmem(fdt->fd);
189out_fdt:
190    kfree(fdt);
191out:
192    return NULL;
193}
194
195/*
196 * Expand the file descriptor table.
197 * This function will allocate a new fdtable and both fd array and fdset, of
198 * the given size.
199 * Return <0 error code on error; 1 on successful completion.
200 * The files->file_lock should be held on entry, and will be held on exit.
201 */
202static int expand_fdtable(struct files_struct *files, int nr)
203    __releases(files->file_lock)
204    __acquires(files->file_lock)
205{
206    struct fdtable *new_fdt, *cur_fdt;
207
208    spin_unlock(&files->file_lock);
209    new_fdt = alloc_fdtable(nr);
210    spin_lock(&files->file_lock);
211    if (!new_fdt)
212        return -ENOMEM;
213    /*
214     * extremely unlikely race - sysctl_nr_open decreased between the check in
215     * caller and alloc_fdtable(). Cheaper to catch it here...
216     */
217    if (unlikely(new_fdt->max_fds <= nr)) {
218        __free_fdtable(new_fdt);
219        return -EMFILE;
220    }
221    /*
222     * Check again since another task may have expanded the fd table while
223     * we dropped the lock
224     */
225    cur_fdt = files_fdtable(files);
226    if (nr >= cur_fdt->max_fds) {
227        /* Continue as planned */
228        copy_fdtable(new_fdt, cur_fdt);
229        rcu_assign_pointer(files->fdt, new_fdt);
230        if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
231            free_fdtable(cur_fdt);
232    } else {
233        /* Somebody else expanded, so undo our attempt */
234        __free_fdtable(new_fdt);
235    }
236    return 1;
237}
238
239/*
240 * Expand files.
241 * This function will expand the file structures, if the requested size exceeds
242 * the current capacity and there is room for expansion.
243 * Return <0 error code on error; 0 when nothing done; 1 when files were
244 * expanded and execution may have blocked.
245 * The files->file_lock should be held on entry, and will be held on exit.
246 */
247int expand_files(struct files_struct *files, int nr)
248{
249    struct fdtable *fdt;
250
251    fdt = files_fdtable(files);
252
253    /*
254     * N.B. For clone tasks sharing a files structure, this test
255     * will limit the total number of files that can be opened.
256     */
257    if (nr >= rlimit(RLIMIT_NOFILE))
258        return -EMFILE;
259
260    /* Do we need to expand? */
261    if (nr < fdt->max_fds)
262        return 0;
263
264    /* Can we expand? */
265    if (nr >= sysctl_nr_open)
266        return -EMFILE;
267
268    /* All good, so we try */
269    return expand_fdtable(files, nr);
270}
271
272static int count_open_files(struct fdtable *fdt)
273{
274    int size = fdt->max_fds;
275    int i;
276
277    /* Find the last open fd */
278    for (i = size/(8*sizeof(long)); i > 0; ) {
279        if (fdt->open_fds->fds_bits[--i])
280            break;
281    }
282    i = (i+1) * 8 * sizeof(long);
283    return i;
284}
285
286/*
287 * Allocate a new files structure and copy contents from the
288 * passed in files structure.
289 * errorp will be valid only when the returned files_struct is NULL.
290 */
291struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
292{
293    struct files_struct *newf;
294    struct file **old_fds, **new_fds;
295    int open_files, size, i;
296    struct fdtable *old_fdt, *new_fdt;
297
298    *errorp = -ENOMEM;
299    newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
300    if (!newf)
301        goto out;
302
303    atomic_set(&newf->count, 1);
304
305    spin_lock_init(&newf->file_lock);
306    newf->next_fd = 0;
307    new_fdt = &newf->fdtab;
308    new_fdt->max_fds = NR_OPEN_DEFAULT;
309    new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
310    new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
311    new_fdt->fd = &newf->fd_array[0];
312    new_fdt->next = NULL;
313
314    spin_lock(&oldf->file_lock);
315    old_fdt = files_fdtable(oldf);
316    open_files = count_open_files(old_fdt);
317
318    /*
319     * Check whether we need to allocate a larger fd array and fd set.
320     */
321    while (unlikely(open_files > new_fdt->max_fds)) {
322        spin_unlock(&oldf->file_lock);
323
324        if (new_fdt != &newf->fdtab)
325            __free_fdtable(new_fdt);
326
327        new_fdt = alloc_fdtable(open_files - 1);
328        if (!new_fdt) {
329            *errorp = -ENOMEM;
330            goto out_release;
331        }
332
333        /* beyond sysctl_nr_open; nothing to do */
334        if (unlikely(new_fdt->max_fds < open_files)) {
335            __free_fdtable(new_fdt);
336            *errorp = -EMFILE;
337            goto out_release;
338        }
339
340        /*
341         * Reacquire the oldf lock and a pointer to its fd table
342         * who knows it may have a new bigger fd table. We need
343         * the latest pointer.
344         */
345        spin_lock(&oldf->file_lock);
346        old_fdt = files_fdtable(oldf);
347        open_files = count_open_files(old_fdt);
348    }
349
350    old_fds = old_fdt->fd;
351    new_fds = new_fdt->fd;
352
353    memcpy(new_fdt->open_fds->fds_bits,
354        old_fdt->open_fds->fds_bits, open_files/8);
355    memcpy(new_fdt->close_on_exec->fds_bits,
356        old_fdt->close_on_exec->fds_bits, open_files/8);
357
358    for (i = open_files; i != 0; i--) {
359        struct file *f = *old_fds++;
360        if (f) {
361            get_file(f);
362        } else {
363            /*
364             * The fd may be claimed in the fd bitmap but not yet
365             * instantiated in the files array if a sibling thread
366             * is partway through open(). So make sure that this
367             * fd is available to the new process.
368             */
369            FD_CLR(open_files - i, new_fdt->open_fds);
370        }
371        rcu_assign_pointer(*new_fds++, f);
372    }
373    spin_unlock(&oldf->file_lock);
374
375    /* compute the remainder to be cleared */
376    size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
377
378    /* This is long word aligned thus could use a optimized version */
379    memset(new_fds, 0, size);
380
381    if (new_fdt->max_fds > open_files) {
382        int left = (new_fdt->max_fds-open_files)/8;
383        int start = open_files / (8 * sizeof(unsigned long));
384
385        memset(&new_fdt->open_fds->fds_bits[start], 0, left);
386        memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
387    }
388
389    rcu_assign_pointer(newf->fdt, new_fdt);
390
391    return newf;
392
393out_release:
394    kmem_cache_free(files_cachep, newf);
395out:
396    return NULL;
397}
398
399static void __devinit fdtable_defer_list_init(int cpu)
400{
401    struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
402    spin_lock_init(&fddef->lock);
403    INIT_WORK(&fddef->wq, free_fdtable_work);
404    fddef->next = NULL;
405}
406
407void __init files_defer_init(void)
408{
409    int i;
410    for_each_possible_cpu(i)
411        fdtable_defer_list_init(i);
412    sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
413                 -BITS_PER_LONG;
414}
415
416struct files_struct init_files = {
417    .count = ATOMIC_INIT(1),
418    .fdt = &init_files.fdtab,
419    .fdtab = {
420        .max_fds = NR_OPEN_DEFAULT,
421        .fd = &init_files.fd_array[0],
422        .close_on_exec = (fd_set *)&init_files.close_on_exec_init,
423        .open_fds = (fd_set *)&init_files.open_fds_init,
424    },
425    .file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
426};
427
428/*
429 * allocate a file descriptor, mark it busy.
430 */
431int alloc_fd(unsigned start, unsigned flags)
432{
433    struct files_struct *files = current->files;
434    unsigned int fd;
435    int error;
436    struct fdtable *fdt;
437
438    spin_lock(&files->file_lock);
439repeat:
440    fdt = files_fdtable(files);
441    fd = start;
442    if (fd < files->next_fd)
443        fd = files->next_fd;
444
445    if (fd < fdt->max_fds)
446        fd = find_next_zero_bit(fdt->open_fds->fds_bits,
447                       fdt->max_fds, fd);
448
449    error = expand_files(files, fd);
450    if (error < 0)
451        goto out;
452
453    /*
454     * If we needed to expand the fs array we
455     * might have blocked - try again.
456     */
457    if (error)
458        goto repeat;
459
460    if (start <= files->next_fd)
461        files->next_fd = fd + 1;
462
463    FD_SET(fd, fdt->open_fds);
464    if (flags & O_CLOEXEC)
465        FD_SET(fd, fdt->close_on_exec);
466    else
467        FD_CLR(fd, fdt->close_on_exec);
468    error = fd;
469#if 1
470    /* Sanity check */
471    if (rcu_dereference_raw(fdt->fd[fd]) != NULL) {
472        printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
473        rcu_assign_pointer(fdt->fd[fd], NULL);
474    }
475#endif
476
477out:
478    spin_unlock(&files->file_lock);
479    return error;
480}
481
482int get_unused_fd(void)
483{
484    return alloc_fd(0, 0);
485}
486EXPORT_SYMBOL(get_unused_fd);
487

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