uio: documentation fixups

[zen-stable.git] / 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/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 <linux/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);
}