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DEFINITIONS
This source file includes following definitions.
- alloc_fdmem
- free_fdarr
- free_fdset
- free_fdtable_work
- free_fdtable_rcu
- copy_fdtable
- alloc_fdtable
- expand_fdtable
- expand_files
- count_open_files
- dup_fd
- fdtable_defer_list_init
- files_defer_init
- alloc_fd
- get_unused_fd
/*
* linux/fs/file.c
*
* Copyright (C) 1998-1999, Stephen Tweedie and Bill Hawes
*
* Manage the dynamic fd arrays in the process files_struct.
*/
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/bitops.h>
#include <linux/interrupt.h>
#include <linux/spinlock.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
struct fdtable_defer {
spinlock_t lock;
struct work_struct wq;
struct fdtable *next;
};
int sysctl_nr_open __read_mostly = 1024*1024;
int sysctl_nr_open_min = BITS_PER_LONG;
int sysctl_nr_open_max = 1024 * 1024; /* raised later */
/*
* We use this list to defer free fdtables that have vmalloced
* sets/arrays. By keeping a per-cpu list, we avoid having to embed
* the work_struct in fdtable itself which avoids a 64 byte (i386) increase in
* this per-task structure.
*/
static DEFINE_PER_CPU(struct fdtable_defer, fdtable_defer_list);
static inline void * alloc_fdmem(unsigned int size)
{
if (size <= PAGE_SIZE)
return kmalloc(size, GFP_KERNEL);
else
return vmalloc(size);
}
static inline void free_fdarr(struct fdtable *fdt)
{
if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *)))
kfree(fdt->fd);
else
vfree(fdt->fd);
}
static inline void free_fdset(struct fdtable *fdt)
{
if (fdt->max_fds <= (PAGE_SIZE * BITS_PER_BYTE / 2))
kfree(fdt->open_fds);
else
vfree(fdt->open_fds);
}
static void free_fdtable_work(struct work_struct *work)
{
struct fdtable_defer *f =
container_of(work, struct fdtable_defer, wq);
struct fdtable *fdt;
spin_lock_bh(&f->lock);
fdt = f->next;
f->next = NULL;
spin_unlock_bh(&f->lock);
while(fdt) {
struct fdtable *next = fdt->next;
vfree(fdt->fd);
free_fdset(fdt);
kfree(fdt);
fdt = next;
}
}
void free_fdtable_rcu(struct rcu_head *rcu)
{
struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
struct fdtable_defer *fddef;
BUG_ON(!fdt);
if (fdt->max_fds <= NR_OPEN_DEFAULT) {
/*
* This fdtable is embedded in the files structure and that
* structure itself is getting destroyed.
*/
kmem_cache_free(files_cachep,
container_of(fdt, struct files_struct, fdtab));
return;
}
if (fdt->max_fds <= (PAGE_SIZE / sizeof(struct file *))) {
kfree(fdt->fd);
kfree(fdt->open_fds);
kfree(fdt);
} else {
fddef = &get_cpu_var(fdtable_defer_list);
spin_lock(&fddef->lock);
fdt->next = fddef->next;
fddef->next = fdt;
/* vmallocs are handled from the workqueue context */
schedule_work(&fddef->wq);
spin_unlock(&fddef->lock);
put_cpu_var(fdtable_defer_list);
}
}
/*
* Expand the fdset in the files_struct. Called with the files spinlock
* held for write.
*/
static void copy_fdtable(struct fdtable *nfdt, struct fdtable *ofdt)
{
unsigned int cpy, set;
BUG_ON(nfdt->max_fds < ofdt->max_fds);
cpy = ofdt->max_fds * sizeof(struct file *);
set = (nfdt->max_fds - ofdt->max_fds) * sizeof(struct file *);
memcpy(nfdt->fd, ofdt->fd, cpy);
memset((char *)(nfdt->fd) + cpy, 0, set);
cpy = ofdt->max_fds / BITS_PER_BYTE;
set = (nfdt->max_fds - ofdt->max_fds) / BITS_PER_BYTE;
memcpy(nfdt->open_fds, ofdt->open_fds, cpy);
memset((char *)(nfdt->open_fds) + cpy, 0, set);
memcpy(nfdt->close_on_exec, ofdt->close_on_exec, cpy);
memset((char *)(nfdt->close_on_exec) + cpy, 0, set);
}
static struct fdtable * alloc_fdtable(unsigned int nr)
{
struct fdtable *fdt;
char *data;
/*
* Figure out how many fds we actually want to support in this fdtable.
* Allocation steps are keyed to the size of the fdarray, since it
* grows far faster than any of the other dynamic data. We try to fit
* the fdarray into comfortable page-tuned chunks: starting at 1024B
* and growing in powers of two from there on.
*/
nr /= (1024 / sizeof(struct file *));
nr = roundup_pow_of_two(nr + 1);
nr *= (1024 / sizeof(struct file *));
/*
* Note that this can drive nr *below* what we had passed if sysctl_nr_open
* had been set lower between the check in expand_files() and here. Deal
* with that in caller, it's cheaper that way.
*
* We make sure that nr remains a multiple of BITS_PER_LONG - otherwise
* bitmaps handling below becomes unpleasant, to put it mildly...
*/
if (unlikely(nr > sysctl_nr_open))
nr = ((sysctl_nr_open - 1) | (BITS_PER_LONG - 1)) + 1;
fdt = kmalloc(sizeof(struct fdtable), GFP_KERNEL);
if (!fdt)
goto out;
fdt->max_fds = nr;
data = alloc_fdmem(nr * sizeof(struct file *));
if (!data)
goto out_fdt;
fdt->fd = (struct file **)data;
data = alloc_fdmem(max_t(unsigned int,
2 * nr / BITS_PER_BYTE, L1_CACHE_BYTES));
if (!data)
goto out_arr;
fdt->open_fds = (fd_set *)data;
data += nr / BITS_PER_BYTE;
fdt->close_on_exec = (fd_set *)data;
INIT_RCU_HEAD(&fdt->rcu);
fdt->next = NULL;
return fdt;
out_arr:
free_fdarr(fdt);
out_fdt:
kfree(fdt);
out:
return NULL;
}
/*
* Expand the file descriptor table.
* This function will allocate a new fdtable and both fd array and fdset, of
* the given size.
* Return <0 error code on error; 1 on successful completion.
* The files->file_lock should be held on entry, and will be held on exit.
*/
static int expand_fdtable(struct files_struct *files, int nr)
__releases(files->file_lock)
__acquires(files->file_lock)
{
struct fdtable *new_fdt, *cur_fdt;
spin_unlock(&files->file_lock);
new_fdt = alloc_fdtable(nr);
spin_lock(&files->file_lock);
if (!new_fdt)
return -ENOMEM;
/*
* extremely unlikely race - sysctl_nr_open decreased between the check in
* caller and alloc_fdtable(). Cheaper to catch it here...
*/
if (unlikely(new_fdt->max_fds <= nr)) {
free_fdarr(new_fdt);
free_fdset(new_fdt);
kfree(new_fdt);
return -EMFILE;
}
/*
* Check again since another task may have expanded the fd table while
* we dropped the lock
*/
cur_fdt = files_fdtable(files);
if (nr >= cur_fdt->max_fds) {
/* Continue as planned */
copy_fdtable(new_fdt, cur_fdt);
rcu_assign_pointer(files->fdt, new_fdt);
if (cur_fdt->max_fds > NR_OPEN_DEFAULT)
free_fdtable(cur_fdt);
} else {
/* Somebody else expanded, so undo our attempt */
free_fdarr(new_fdt);
free_fdset(new_fdt);
kfree(new_fdt);
}
return 1;
}
/*
* Expand files.
* This function will expand the file structures, if the requested size exceeds
* the current capacity and there is room for expansion.
* Return <0 error code on error; 0 when nothing done; 1 when files were
* expanded and execution may have blocked.
* The files->file_lock should be held on entry, and will be held on exit.
*/
int expand_files(struct files_struct *files, int nr)
{
struct fdtable *fdt;
fdt = files_fdtable(files);
/*
* N.B. For clone tasks sharing a files structure, this test
* will limit the total number of files that can be opened.
*/
if (nr >= current->signal->rlim[RLIMIT_NOFILE].rlim_cur)
return -EMFILE;
/* Do we need to expand? */
if (nr < fdt->max_fds)
return 0;
/* Can we expand? */
if (nr >= sysctl_nr_open)
return -EMFILE;
/* All good, so we try */
return expand_fdtable(files, nr);
}
static int count_open_files(struct fdtable *fdt)
{
int size = fdt->max_fds;
int i;
/* Find the last open fd */
for (i = size/(8*sizeof(long)); i > 0; ) {
if (fdt->open_fds->fds_bits[--i])
break;
}
i = (i+1) * 8 * sizeof(long);
return i;
}
/*
* Allocate a new files structure and copy contents from the
* passed in files structure.
* errorp will be valid only when the returned files_struct is NULL.
*/
struct files_struct *dup_fd(struct files_struct *oldf, int *errorp)
{
struct files_struct *newf;
struct file **old_fds, **new_fds;
int open_files, size, i;
struct fdtable *old_fdt, *new_fdt;
*errorp = -ENOMEM;
newf = kmem_cache_alloc(files_cachep, GFP_KERNEL);
if (!newf)
goto out;
atomic_set(&newf->count, 1);
spin_lock_init(&newf->file_lock);
newf->next_fd = 0;
new_fdt = &newf->fdtab;
new_fdt->max_fds = NR_OPEN_DEFAULT;
new_fdt->close_on_exec = (fd_set *)&newf->close_on_exec_init;
new_fdt->open_fds = (fd_set *)&newf->open_fds_init;
new_fdt->fd = &newf->fd_array[0];
INIT_RCU_HEAD(&new_fdt->rcu);
new_fdt->next = NULL;
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
open_files = count_open_files(old_fdt);
/*
* Check whether we need to allocate a larger fd array and fd set.
*/
while (unlikely(open_files > new_fdt->max_fds)) {
spin_unlock(&oldf->file_lock);
if (new_fdt != &newf->fdtab) {
free_fdarr(new_fdt);
free_fdset(new_fdt);
kfree(new_fdt);
}
new_fdt = alloc_fdtable(open_files - 1);
if (!new_fdt) {
*errorp = -ENOMEM;
goto out_release;
}
/* beyond sysctl_nr_open; nothing to do */
if (unlikely(new_fdt->max_fds < open_files)) {
free_fdarr(new_fdt);
free_fdset(new_fdt);
kfree(new_fdt);
*errorp = -EMFILE;
goto out_release;
}
/*
* Reacquire the oldf lock and a pointer to its fd table
* who knows it may have a new bigger fd table. We need
* the latest pointer.
*/
spin_lock(&oldf->file_lock);
old_fdt = files_fdtable(oldf);
open_files = count_open_files(old_fdt);
}
old_fds = old_fdt->fd;
new_fds = new_fdt->fd;
memcpy(new_fdt->open_fds->fds_bits,
old_fdt->open_fds->fds_bits, open_files/8);
memcpy(new_fdt->close_on_exec->fds_bits,
old_fdt->close_on_exec->fds_bits, open_files/8);
for (i = open_files; i != 0; i--) {
struct file *f = *old_fds++;
if (f) {
get_file(f);
} else {
/*
* The fd may be claimed in the fd bitmap but not yet
* instantiated in the files array if a sibling thread
* is partway through open(). So make sure that this
* fd is available to the new process.
*/
FD_CLR(open_files - i, new_fdt->open_fds);
}
rcu_assign_pointer(*new_fds++, f);
}
spin_unlock(&oldf->file_lock);
/* compute the remainder to be cleared */
size = (new_fdt->max_fds - open_files) * sizeof(struct file *);
/* This is long word aligned thus could use a optimized version */
memset(new_fds, 0, size);
if (new_fdt->max_fds > open_files) {
int left = (new_fdt->max_fds-open_files)/8;
int start = open_files / (8 * sizeof(unsigned long));
memset(&new_fdt->open_fds->fds_bits[start], 0, left);
memset(&new_fdt->close_on_exec->fds_bits[start], 0, left);
}
rcu_assign_pointer(newf->fdt, new_fdt);
return newf;
out_release:
kmem_cache_free(files_cachep, newf);
out:
return NULL;
}
static void __devinit fdtable_defer_list_init(int cpu)
{
struct fdtable_defer *fddef = &per_cpu(fdtable_defer_list, cpu);
spin_lock_init(&fddef->lock);
INIT_WORK(&fddef->wq, free_fdtable_work);
fddef->next = NULL;
}
void __init files_defer_init(void)
{
int i;
for_each_possible_cpu(i)
fdtable_defer_list_init(i);
sysctl_nr_open_max = min((size_t)INT_MAX, ~(size_t)0/sizeof(void *)) &
-BITS_PER_LONG;
}
struct files_struct init_files = {
.count = ATOMIC_INIT(1),
.fdt = &init_files.fdtab,
.fdtab = {
.max_fds = NR_OPEN_DEFAULT,
.fd = &init_files.fd_array[0],
.close_on_exec = (fd_set *)&init_files.close_on_exec_init,
.open_fds = (fd_set *)&init_files.open_fds_init,
.rcu = RCU_HEAD_INIT,
},
.file_lock = __SPIN_LOCK_UNLOCKED(init_task.file_lock),
};
/*
* allocate a file descriptor, mark it busy.
*/
int alloc_fd(unsigned start, unsigned flags)
{
struct files_struct *files = current->files;
unsigned int fd;
int error;
struct fdtable *fdt;
spin_lock(&files->file_lock);
repeat:
fdt = files_fdtable(files);
fd = start;
if (fd < files->next_fd)
fd = files->next_fd;
if (fd < fdt->max_fds)
fd = find_next_zero_bit(fdt->open_fds->fds_bits,
fdt->max_fds, fd);
error = expand_files(files, fd);
if (error < 0)
goto out;
/*
* If we needed to expand the fs array we
* might have blocked - try again.
*/
if (error)
goto repeat;
if (start <= files->next_fd)
files->next_fd = fd + 1;
FD_SET(fd, fdt->open_fds);
if (flags & O_CLOEXEC)
FD_SET(fd, fdt->close_on_exec);
else
FD_CLR(fd, fdt->close_on_exec);
error = fd;
#if 1
/* Sanity check */
if (rcu_dereference(fdt->fd[fd]) != NULL) {
printk(KERN_WARNING "alloc_fd: slot %d not NULL!\n", fd);
rcu_assign_pointer(fdt->fd[fd], NULL);
}
#endif
out:
spin_unlock(&files->file_lock);
return error;
}
int get_unused_fd(void)
{
return alloc_fd(0, 0);
}
EXPORT_SYMBOL(get_unused_fd);