linux/fs/file.c

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/*
* 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/fs.h>
#include <linux/mm.h>
#include <linux/time.h>
#include <linux/slab.h>
#include <linux/vmalloc.h>
#include <linux/file.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 timer_list timer;
struct fdtable *next;
};
/*
* 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);
/*
* Allocate an fd array, using kmalloc or vmalloc.
* Note: the array isn't cleared at allocation time.
*/
struct file ** alloc_fd_array(int num)
{
struct file **new_fds;
int size = num * sizeof(struct file *);
if (size <= PAGE_SIZE)
new_fds = (struct file **) kmalloc(size, GFP_KERNEL);
else
new_fds = (struct file **) vmalloc(size);
return new_fds;
}
void free_fd_array(struct file **array, int num)
{
int size = num * sizeof(struct file *);
if (!array) {
printk (KERN_ERR "free_fd_array: array = 0 (num = %d)\n", num);
return;
}
if (num <= NR_OPEN_DEFAULT) /* Don't free the embedded fd array! */
return;
else if (size <= PAGE_SIZE)
kfree(array);
else
vfree(array);
}
static void __free_fdtable(struct fdtable *fdt)
{
free_fdset(fdt->open_fds, fdt->max_fdset);
free_fdset(fdt->close_on_exec, fdt->max_fdset);
free_fd_array(fdt->fd, fdt->max_fds);
kfree(fdt);
}
static void fdtable_timer(unsigned long data)
{
struct fdtable_defer *fddef = (struct fdtable_defer *)data;
spin_lock(&fddef->lock);
/*
* If someone already emptied the queue return.
*/
if (!fddef->next)
goto out;
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
out:
spin_unlock(&fddef->lock);
}
static void free_fdtable_work(struct fdtable_defer *f)
{
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;
__free_fdtable(fdt);
fdt = next;
}
}
static void free_fdtable_rcu(struct rcu_head *rcu)
{
struct fdtable *fdt = container_of(rcu, struct fdtable, rcu);
int fdset_size, fdarray_size;
struct fdtable_defer *fddef;
BUG_ON(!fdt);
fdset_size = fdt->max_fdset / 8;
fdarray_size = fdt->max_fds * sizeof(struct file *);
if (fdt->free_files) {
/*
* The this fdtable was embedded in the files structure
* and the files structure itself was getting destroyed.
* It is now safe to free the files structure.
*/
kmem_cache_free(files_cachep, fdt->free_files);
return;
}
if (fdt->max_fdset <= EMBEDDED_FD_SET_SIZE &&
fdt->max_fds <= NR_OPEN_DEFAULT) {
/*
* The fdtable was embedded
*/
return;
}
if (fdset_size <= PAGE_SIZE && fdarray_size <= PAGE_SIZE) {
kfree(fdt->open_fds);
kfree(fdt->close_on_exec);
kfree(fdt->fd);
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.
* If the per-cpu workqueue is running, then we
* defer work scheduling through a timer.
*/
if (!schedule_work(&fddef->wq))
mod_timer(&fddef->timer, 5);
spin_unlock(&fddef->lock);
put_cpu_var(fdtable_defer_list);
}
}
void free_fdtable(struct fdtable *fdt)
{
if (fdt->free_files ||
fdt->max_fdset > EMBEDDED_FD_SET_SIZE ||
fdt->max_fds > NR_OPEN_DEFAULT)
call_rcu(&fdt->rcu, free_fdtable_rcu);
}
/*
* Expand the fdset in the files_struct. Called with the files spinlock
* held for write.
*/
static void copy_fdtable(struct fdtable *nfdt, struct fdtable *fdt)
{
int i;
int count;
BUG_ON(nfdt->max_fdset < fdt->max_fdset);
BUG_ON(nfdt->max_fds < fdt->max_fds);
/* Copy the existing tables and install the new pointers */
i = fdt->max_fdset / (sizeof(unsigned long) * 8);
count = (nfdt->max_fdset - fdt->max_fdset) / 8;
/*
* Don't copy the entire array if the current fdset is
* not yet initialised.
*/
if (i) {
memcpy (nfdt->open_fds, fdt->open_fds,
fdt->max_fdset/8);
memcpy (nfdt->close_on_exec, fdt->close_on_exec,
fdt->max_fdset/8);
memset (&nfdt->open_fds->fds_bits[i], 0, count);
memset (&nfdt->close_on_exec->fds_bits[i], 0, count);
}
/* Don't copy/clear the array if we are creating a new
fd array for fork() */
if (fdt->max_fds) {
memcpy(nfdt->fd, fdt->fd,
fdt->max_fds * sizeof(struct file *));
/* clear the remainder of the array */
memset(&nfdt->fd[fdt->max_fds], 0,
(nfdt->max_fds - fdt->max_fds) *
sizeof(struct file *));
}
}
/*
* Allocate an fdset array, using kmalloc or vmalloc.
* Note: the array isn't cleared at allocation time.
*/
fd_set * alloc_fdset(int num)
{
fd_set *new_fdset;
int size = num / 8;
if (size <= PAGE_SIZE)
new_fdset = (fd_set *) kmalloc(size, GFP_KERNEL);
else
new_fdset = (fd_set *) vmalloc(size);
return new_fdset;
}
void free_fdset(fd_set *array, int num)
{
if (num <= EMBEDDED_FD_SET_SIZE) /* Don't free an embedded fdset */
return;
else if (num <= 8 * PAGE_SIZE)
kfree(array);
else
vfree(array);
}
static struct fdtable *alloc_fdtable(int nr)
{
struct fdtable *fdt = NULL;
int nfds = 0;
fd_set *new_openset = NULL, *new_execset = NULL;
struct file **new_fds;
fdt = kzalloc(sizeof(*fdt), GFP_KERNEL);
if (!fdt)
goto out;
nfds = max_t(int, 8 * L1_CACHE_BYTES, roundup_pow_of_two(nr + 1));
if (nfds > NR_OPEN)
nfds = NR_OPEN;
new_openset = alloc_fdset(nfds);
new_execset = alloc_fdset(nfds);
if (!new_openset || !new_execset)
goto out;
fdt->open_fds = new_openset;
fdt->close_on_exec = new_execset;
fdt->max_fdset = nfds;
nfds = NR_OPEN_DEFAULT;
/*
* Expand to the max in easy steps, and keep expanding it until
* we have enough for the requested fd array size.
*/
do {
#if NR_OPEN_DEFAULT < 256
if (nfds < 256)
nfds = 256;
else
#endif
if (nfds < (PAGE_SIZE / sizeof(struct file *)))
nfds = PAGE_SIZE / sizeof(struct file *);
else {
nfds = nfds * 2;
if (nfds > NR_OPEN)
nfds = NR_OPEN;
}
} while (nfds <= nr);
new_fds = alloc_fd_array(nfds);
if (!new_fds)
goto out2;
fdt->fd = new_fds;
fdt->max_fds = nfds;
fdt->free_files = NULL;
return fdt;
out2:
nfds = fdt->max_fdset;
out:
free_fdset(new_openset, nfds);
free_fdset(new_execset, nfds);
kfree(fdt);
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;
/*
* 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 || nr >= cur_fdt->max_fdset) {
/* Continue as planned */
copy_fdtable(new_fdt, cur_fdt);
rcu_assign_pointer(files->fdt, new_fdt);
free_fdtable(cur_fdt);
} else {
/* Somebody else expanded, so undo our attempt */
__free_fdtable(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);
/* Do we need to expand? */
if (nr < fdt->max_fdset && nr < fdt->max_fds)
return 0;
/* Can we expand? */
if (fdt->max_fdset >= NR_OPEN || fdt->max_fds >= NR_OPEN ||
nr >= NR_OPEN)
return -EMFILE;
/* All good, so we try */
return expand_fdtable(files, nr);
}
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, (void (*)(void *))free_fdtable_work, fddef);
init_timer(&fddef->timer);
fddef->timer.data = (unsigned long)fddef;
fddef->timer.function = fdtable_timer;
fddef->next = NULL;
}
void __init files_defer_init(void)
{
int i;
for_each_possible_cpu(i)
fdtable_defer_list_init(i);
}