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executable file 555 lines (486 sloc) 13.521 kb
/*
* linux/fs/file_table.c
*
* Copyright (C) 1991, 1992 Linus Torvalds
* Copyright (C) 1997 David S. Miller (davem@caip.rutgers.edu)
*/
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/file.h>
#include <linux/fdtable.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/fs.h>
#include <linux/security.h>
#include <linux/eventpoll.h>
#include <linux/rcupdate.h>
#include <linux/mount.h>
#include <linux/capability.h>
#include <linux/cdev.h>
#include <linux/fsnotify.h>
#include <linux/sysctl.h>
#include <linux/lglock.h>
#include <linux/percpu_counter.h>
#include <linux/percpu.h>
#include <linux/ima.h>
#include <asm/atomic.h>
#include "internal.h"
/* sysctl tunables... */
struct files_stat_struct files_stat = {
.max_files = NR_FILE
};
DECLARE_LGLOCK(files_lglock);
DEFINE_LGLOCK(files_lglock);
/* SLAB cache for file structures */
static struct kmem_cache *filp_cachep __read_mostly;
static struct percpu_counter nr_files __cacheline_aligned_in_smp;
static inline void file_free_rcu(struct rcu_head *head)
{
struct file *f = container_of(head, struct file, f_u.fu_rcuhead);
put_cred(f->f_cred);
kmem_cache_free(filp_cachep, f);
}
static inline void file_free(struct file *f)
{
percpu_counter_dec(&nr_files);
file_check_state(f);
call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}
/*
* Return the total number of open files in the system
*/
static long get_nr_files(void)
{
return percpu_counter_read_positive(&nr_files);
}
/*
* Return the maximum number of open files in the system
*/
unsigned long get_max_files(void)
{
return files_stat.max_files;
}
EXPORT_SYMBOL_GPL(get_max_files);
/*
* Handle nr_files sysctl
*/
#if defined(CONFIG_SYSCTL) && defined(CONFIG_PROC_FS)
int proc_nr_files(ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
files_stat.nr_files = get_nr_files();
return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
}
#else
int proc_nr_files(ctl_table *table, int write,
void __user *buffer, size_t *lenp, loff_t *ppos)
{
return -ENOSYS;
}
#endif
/* Find an unused file structure and return a pointer to it.
* Returns NULL, if there are no more free file structures or
* we run out of memory.
*
* Be very careful using this. You are responsible for
* getting write access to any mount that you might assign
* to this filp, if it is opened for write. If this is not
* done, you will imbalance int the mount's writer count
* and a warning at __fput() time.
*/
struct file *get_empty_filp(void)
{
const struct cred *cred = current_cred();
static long old_max;
struct file * f;
/*
* Privileged users can go above max_files
*/
if (get_nr_files() >= files_stat.max_files && !capable(CAP_SYS_ADMIN)) {
/*
* percpu_counters are inaccurate. Do an expensive check before
* we go and fail.
*/
if (percpu_counter_sum_positive(&nr_files) >= files_stat.max_files)
goto over;
}
f = kmem_cache_zalloc(filp_cachep, GFP_KERNEL);
if (f == NULL)
goto fail;
percpu_counter_inc(&nr_files);
f->f_cred = get_cred(cred);
if (security_file_alloc(f))
goto fail_sec;
INIT_LIST_HEAD(&f->f_u.fu_list);
atomic_long_set(&f->f_count, 1);
rwlock_init(&f->f_owner.lock);
spin_lock_init(&f->f_lock);
eventpoll_init_file(f);
/* f->f_version: 0 */
return f;
over:
/* Ran out of filps - report that */
if (get_nr_files() > old_max) {
pr_info("VFS: file-max limit %lu reached\n", get_max_files());
old_max = get_nr_files();
}
goto fail;
fail_sec:
file_free(f);
fail:
return NULL;
}
/**
* alloc_file - allocate and initialize a 'struct file'
* @mnt: the vfsmount on which the file will reside
* @dentry: the dentry representing the new file
* @mode: the mode with which the new file will be opened
* @fop: the 'struct file_operations' for the new file
*
* Use this instead of get_empty_filp() to get a new
* 'struct file'. Do so because of the same initialization
* pitfalls reasons listed for init_file(). This is a
* preferred interface to using init_file().
*
* If all the callers of init_file() are eliminated, its
* code should be moved into this function.
*/
struct file *alloc_file(struct path *path, fmode_t mode,
const struct file_operations *fop)
{
struct file *file;
file = get_empty_filp();
if (!file)
return NULL;
file->f_path = *path;
file->f_mapping = path->dentry->d_inode->i_mapping;
file->f_mode = mode;
file->f_op = fop;
/*
* These mounts don't really matter in practice
* for r/o bind mounts. They aren't userspace-
* visible. We do this for consistency, and so
* that we can do debugging checks at __fput()
*/
if ((mode & FMODE_WRITE) && !special_file(path->dentry->d_inode->i_mode)) {
file_take_write(file);
WARN_ON(mnt_clone_write(path->mnt));
}
if ((mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
i_readcount_inc(path->dentry->d_inode);
return file;
}
EXPORT_SYMBOL(alloc_file);
/**
* drop_file_write_access - give up ability to write to a file
* @file: the file to which we will stop writing
*
* This is a central place which will give up the ability
* to write to @file, along with access to write through
* its vfsmount.
*/
void drop_file_write_access(struct file *file)
{
struct vfsmount *mnt = file->f_path.mnt;
struct dentry *dentry = file->f_path.dentry;
struct inode *inode = dentry->d_inode;
put_write_access(inode);
if (special_file(inode->i_mode))
return;
if (file_check_writeable(file) != 0)
return;
mnt_drop_write(mnt);
file_release_write(file);
}
EXPORT_SYMBOL_GPL(drop_file_write_access);
/* the real guts of fput() - releasing the last reference to file
*/
static void __fput(struct file *file)
{
struct dentry *dentry = file->f_path.dentry;
struct vfsmount *mnt = file->f_path.mnt;
struct inode *inode = dentry->d_inode;
might_sleep();
fsnotify_close(file);
/*
* The function eventpoll_release() should be the first called
* in the file cleanup chain.
*/
eventpoll_release(file);
locks_remove_flock(file);
if (unlikely(file->f_flags & FASYNC)) {
if (file->f_op && file->f_op->fasync)
file->f_op->fasync(-1, file, 0);
}
if (file->f_op && file->f_op->release)
file->f_op->release(inode, file);
security_file_free(file);
ima_file_free(file);
if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL &&
!(file->f_mode & FMODE_PATH))) {
cdev_put(inode->i_cdev);
}
fops_put(file->f_op);
put_pid(file->f_owner.pid);
file_sb_list_del(file);
if ((file->f_mode & (FMODE_READ | FMODE_WRITE)) == FMODE_READ)
i_readcount_dec(inode);
if (file->f_mode & FMODE_WRITE)
drop_file_write_access(file);
file->f_path.dentry = NULL;
file->f_path.mnt = NULL;
file_free(file);
dput(dentry);
mntput(mnt);
}
void fput(struct file *file)
{
if (atomic_long_dec_and_test(&file->f_count))
__fput(file);
}
EXPORT_SYMBOL(fput);
struct file *fget(unsigned int fd)
{
struct file *file;
struct files_struct *files = current->files;
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
/* File object ref couldn't be taken */
if (file->f_mode & FMODE_PATH ||
!atomic_long_inc_not_zero(&file->f_count))
file = NULL;
}
rcu_read_unlock();
return file;
}
EXPORT_SYMBOL(fget);
struct file *fget_raw(unsigned int fd)
{
struct file *file;
struct files_struct *files = current->files;
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
/* File object ref couldn't be taken */
if (!atomic_long_inc_not_zero(&file->f_count))
file = NULL;
}
rcu_read_unlock();
return file;
}
EXPORT_SYMBOL(fget_raw);
/*
* Lightweight file lookup - no refcnt increment if fd table isn't shared.
*
* You can use this instead of fget if you satisfy all of the following
* conditions:
* 1) You must call fput_light before exiting the syscall and returning control
* to userspace (i.e. you cannot remember the returned struct file * after
* returning to userspace).
* 2) You must not call filp_close on the returned struct file * in between
* calls to fget_light and fput_light.
* 3) You must not clone the current task in between the calls to fget_light
* and fput_light.
*
* The fput_needed flag returned by fget_light should be passed to the
* corresponding fput_light.
*/
struct file *fget_light(unsigned int fd, int *fput_needed)
{
struct file *file;
struct files_struct *files = current->files;
*fput_needed = 0;
if (atomic_read(&files->count) == 1) {
file = fcheck_files(files, fd);
if (file && (file->f_mode & FMODE_PATH))
file = NULL;
} else {
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
if (!(file->f_mode & FMODE_PATH) &&
atomic_long_inc_not_zero(&file->f_count))
*fput_needed = 1;
else
/* Didn't get the reference, someone's freed */
file = NULL;
}
rcu_read_unlock();
}
return file;
}
struct file *fget_raw_light(unsigned int fd, int *fput_needed)
{
struct file *file;
struct files_struct *files = current->files;
*fput_needed = 0;
if (atomic_read(&files->count) == 1) {
file = fcheck_files(files, fd);
} else {
rcu_read_lock();
file = fcheck_files(files, fd);
if (file) {
if (atomic_long_inc_not_zero(&file->f_count))
*fput_needed = 1;
else
/* Didn't get the reference, someone's freed */
file = NULL;
}
rcu_read_unlock();
}
return file;
}
void put_filp(struct file *file)
{
if (atomic_long_dec_and_test(&file->f_count)) {
security_file_free(file);
file_sb_list_del(file);
file_free(file);
}
}
static inline int file_list_cpu(struct file *file)
{
#ifdef CONFIG_SMP
return file->f_sb_list_cpu;
#else
return smp_processor_id();
#endif
}
/* helper for file_sb_list_add to reduce ifdefs */
static inline void __file_sb_list_add(struct file *file, struct super_block *sb)
{
struct list_head *list;
#ifdef CONFIG_SMP
int cpu;
cpu = smp_processor_id();
file->f_sb_list_cpu = cpu;
list = per_cpu_ptr(sb->s_files, cpu);
#else
list = &sb->s_files;
#endif
list_add(&file->f_u.fu_list, list);
}
/**
* file_sb_list_add - add a file to the sb's file list
* @file: file to add
* @sb: sb to add it to
*
* Use this function to associate a file with the superblock of the inode it
* refers to.
*/
void file_sb_list_add(struct file *file, struct super_block *sb)
{
lg_local_lock(files_lglock);
__file_sb_list_add(file, sb);
lg_local_unlock(files_lglock);
}
/**
* file_sb_list_del - remove a file from the sb's file list
* @file: file to remove
* @sb: sb to remove it from
*
* Use this function to remove a file from its superblock.
*/
void file_sb_list_del(struct file *file)
{
if (!list_empty(&file->f_u.fu_list)) {
lg_local_lock_cpu(files_lglock, file_list_cpu(file));
list_del_init(&file->f_u.fu_list);
lg_local_unlock_cpu(files_lglock, file_list_cpu(file));
}
}
#ifdef CONFIG_SMP
/*
* These macros iterate all files on all CPUs for a given superblock.
* files_lglock must be held globally.
*/
#define do_file_list_for_each_entry(__sb, __file) \
{ \
int i; \
for_each_possible_cpu(i) { \
struct list_head *list; \
list = per_cpu_ptr((__sb)->s_files, i); \
list_for_each_entry((__file), list, f_u.fu_list)
#define while_file_list_for_each_entry \
} \
}
#else
#define do_file_list_for_each_entry(__sb, __file) \
{ \
struct list_head *list; \
list = &(sb)->s_files; \
list_for_each_entry((__file), list, f_u.fu_list)
#define while_file_list_for_each_entry \
}
#endif
int fs_may_remount_ro(struct super_block *sb)
{
struct file *file;
/* Check that no files are currently opened for writing. */
lg_global_lock(files_lglock);
do_file_list_for_each_entry(sb, file) {
struct inode *inode = file->f_path.dentry->d_inode;
/* File with pending delete? */
if (inode->i_nlink == 0)
goto too_bad;
/* Writeable file? */
if (S_ISREG(inode->i_mode) && (file->f_mode & FMODE_WRITE))
goto too_bad;
} while_file_list_for_each_entry;
lg_global_unlock(files_lglock);
return 1; /* Tis' cool bro. */
too_bad:
lg_global_unlock(files_lglock);
return 0;
}
/**
* mark_files_ro - mark all files read-only
* @sb: superblock in question
*
* All files are marked read-only. We don't care about pending
* delete files so this should be used in 'force' mode only.
*/
void mark_files_ro(struct super_block *sb)
{
struct file *f;
retry:
lg_global_lock(files_lglock);
do_file_list_for_each_entry(sb, f) {
struct vfsmount *mnt;
if (!S_ISREG(f->f_path.dentry->d_inode->i_mode))
continue;
if (!file_count(f))
continue;
if (!(f->f_mode & FMODE_WRITE))
continue;
spin_lock(&f->f_lock);
f->f_mode &= ~FMODE_WRITE;
spin_unlock(&f->f_lock);
if (file_check_writeable(f) != 0)
continue;
file_release_write(f);
mnt = mntget(f->f_path.mnt);
/* This can sleep, so we can't hold the spinlock. */
lg_global_unlock(files_lglock);
mnt_drop_write(mnt);
mntput(mnt);
goto retry;
} while_file_list_for_each_entry;
lg_global_unlock(files_lglock);
}
void __init files_init(unsigned long mempages)
{
unsigned long n;
filp_cachep = kmem_cache_create("filp", sizeof(struct file), 0,
SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
/*
* One file with associated inode and dcache is very roughly 1K.
* Per default don't use more than 10% of our memory for files.
*/
n = (mempages * (PAGE_SIZE / 1024)) / 10;
files_stat.max_files = max_t(unsigned long, n, NR_FILE);
files_defer_init();
lg_lock_init(files_lglock);
percpu_counter_init(&nr_files, 0);
}
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