[safe/jmp/linux-2.6] / fs / file_table.c

/*
 *  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/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/percpu_counter.h>

#include <asm/atomic.h>

/* sysctl tunables... */
struct files_stat_struct files_stat = {
        .max_files = NR_FILE
};

/* public. Not pretty! */
__cacheline_aligned_in_smp DEFINE_SPINLOCK(files_lock);

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);
        kmem_cache_free(filp_cachep, f);
}

static inline void file_free(struct file *f)
{
        percpu_counter_dec(&nr_files);
        call_rcu(&f->f_u.fu_rcuhead, file_free_rcu);
}

/*
 * Return the total number of open files in the system
 */
static int get_nr_files(void)
{
        return percpu_counter_read_positive(&nr_files);
}

/*
 * Return the maximum number of open files in the system
 */
int 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, struct file *filp,
                     void __user *buffer, size_t *lenp, loff_t *ppos)
{
        files_stat.nr_files = get_nr_files();
        return proc_dointvec(table, write, filp, buffer, lenp, ppos);
}
#else
int proc_nr_files(ctl_table *table, int write, struct file *filp,
                     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)
{
        struct task_struct *tsk;
        static int 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);
        if (security_file_alloc(f))
                goto fail_sec;

        tsk = current;
        INIT_LIST_HEAD(&f->f_u.fu_list);
        atomic_set(&f->f_count, 1);
        rwlock_init(&f->f_owner.lock);
        f->f_uid = tsk->fsuid;
        f->f_gid = tsk->fsgid;
        eventpoll_init_file(f);
        /* f->f_version: 0 */
        return f;

over:
        /* Ran out of filps - report that */
        if (get_nr_files() > old_max) {
                printk(KERN_INFO "VFS: file-max limit %d reached\n",
                                        get_max_files());
                old_max = get_nr_files();
        }
        goto fail;

fail_sec:
        file_free(f);
fail:
        return NULL;
}

EXPORT_SYMBOL(get_empty_filp);

/**
 * 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 vfsmount *mnt, struct dentry *dentry,
                mode_t mode, const struct file_operations *fop)
{
        struct file *file;
        struct path;

        file = get_empty_filp();
        if (!file)
                return NULL;

        init_file(file, mnt, dentry, mode, fop);
        return file;
}
EXPORT_SYMBOL(alloc_file);

/**
 * init_file - initialize a 'struct file'
 * @file: the already allocated 'struct file' to initialized
 * @mnt: the vfsmount on which the file resides
 * @dentry: the dentry representing this file
 * @mode: the mode the file is opened with
 * @fop: the 'struct file_operations' for this file
 *
 * Use this instead of setting the members directly.  Doing so
 * avoids making mistakes like forgetting the mntget() or
 * forgetting to take a write on the mnt.
 *
 * Note: This is a crappy interface.  It is here to make
 * merging with the existing users of get_empty_filp()
 * who have complex failure logic easier.  All users
 * of this should be moving to alloc_file().
 */
int init_file(struct file *file, struct vfsmount *mnt, struct dentry *dentry,
           mode_t mode, const struct file_operations *fop)
{
        int error = 0;
        file->f_path.dentry = dentry;
        file->f_path.mnt = mntget(mnt);
        file->f_mapping = 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(dentry->d_inode->i_mode)) {
                error = mnt_want_write(mnt);
                WARN_ON(error);
        }
        return error;
}
EXPORT_SYMBOL(init_file);

void fput(struct file *file)
{
        if (atomic_dec_and_test(&file->f_count))
                __fput(file);
}

EXPORT_SYMBOL(fput);

/**
 * 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))
                mnt_drop_write(mnt);
}
EXPORT_SYMBOL_GPL(drop_file_write_access);

/* __fput is called from task context when aio completion releases the last
 * last use of a struct file *.  Do not use otherwise.
 */
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 (file->f_op && file->f_op->release)
                file->f_op->release(inode, file);
        security_file_free(file);
        if (unlikely(S_ISCHR(inode->i_mode) && inode->i_cdev != NULL))
                cdev_put(inode->i_cdev);
        fops_put(file->f_op);
        put_pid(file->f_owner.pid);
        file_kill(file);
        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);
}

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) {
                if (!atomic_inc_not_zero(&file->f_count)) {
                        /* File object ref couldn't be taken */
                        rcu_read_unlock();
                        return NULL;
                }
        }
        rcu_read_unlock();

        return file;
}

EXPORT_SYMBOL(fget);

/*
 * Lightweight file lookup - no refcnt increment if fd table isn't shared. 
 * You can use this only if it is guranteed that the current task already 
 * holds a refcnt to that file. That check has to be done at fget() only
 * and a flag is returned to be passed to the corresponding fput_light().
 * There must not be a cloning between an fget_light/fput_light pair.
 */
struct file *fget_light(unsigned int fd, int *fput_needed)
{
        struct file *file;
        struct files_struct *files = current->files;

        *fput_needed = 0;
        if (likely((atomic_read(&files->count) == 1))) {
                file = fcheck_files(files, fd);
        } else {
                rcu_read_lock();
                file = fcheck_files(files, fd);
                if (file) {
                        if (atomic_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_dec_and_test(&file->f_count)) {
                security_file_free(file);
                file_kill(file);
                file_free(file);
        }
}

void file_move(struct file *file, struct list_head *list)
{
        if (!list)
                return;
        file_list_lock();
        list_move(&file->f_u.fu_list, list);
        file_list_unlock();
}

void file_kill(struct file *file)
{
        if (!list_empty(&file->f_u.fu_list)) {
                file_list_lock();
                list_del_init(&file->f_u.fu_list);
                file_list_unlock();
        }
}

int fs_may_remount_ro(struct super_block *sb)
{
        struct file *file;

        /* Check that no files are currently opened for writing. */
        file_list_lock();
        list_for_each_entry(file, &sb->s_files, f_u.fu_list) {
                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;
        }
        file_list_unlock();
        return 1; /* Tis' cool bro. */
too_bad:
        file_list_unlock();
        return 0;
}

void __init files_init(unsigned long mempages)
{ 
        int n; 
        /* 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 = n; 
        if (files_stat.max_files < NR_FILE)
                files_stat.max_files = NR_FILE;
        files_defer_init();
        percpu_counter_init(&nr_files, 0);
}