root/fs/dnotify.c

/*
 * Directory notifications for Linux.
 *
 * Copyright (C) 2000,2001,2002 Stephen Rothwell
 *
 * This program is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by the
 * Free Software Foundation; either version 2, or (at your option) any
 * later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 */
#include <linux/fs.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/dnotify.h>
#include <linux/init.h>
#include <linux/spinlock.h>
#include <linux/slab.h>

int dir_notify_enable = 1;

static rwlock_t dn_lock = RW_LOCK_UNLOCKED;
static kmem_cache_t *dn_cache;

static void redo_inode_mask(struct inode *inode)
{
        unsigned long new_mask;
        struct dnotify_struct *dn;

        new_mask = 0;
        for (dn = inode->i_dnotify; dn != NULL; dn = dn->dn_next)
                new_mask |= dn->dn_mask & ~DN_MULTISHOT;
        inode->i_dnotify_mask = new_mask;
}

void dnotify_flush(struct file *filp, fl_owner_t id)
{
        struct dnotify_struct *dn;
        struct dnotify_struct **prev;
        struct inode *inode;

        inode = filp->f_dentry->d_inode;
        if (!S_ISDIR(inode->i_mode))
                return;
        write_lock(&dn_lock);
        prev = &inode->i_dnotify;
        while ((dn = *prev) != NULL) {
                if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
                        *prev = dn->dn_next;
                        redo_inode_mask(inode);
                        kmem_cache_free(dn_cache, dn);
                        break;
                }
                prev = &dn->dn_next;
        }
        write_unlock(&dn_lock);
}

int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
{
        struct dnotify_struct *dn;
        struct dnotify_struct *odn;
        struct dnotify_struct **prev;
        struct inode *inode;
        fl_owner_t id = current->files;
        int error = 0;

        if ((arg & ~DN_MULTISHOT) == 0) {
                dnotify_flush(filp, id);
                return 0;
        }
        if (!dir_notify_enable)
                return -EINVAL;
        inode = filp->f_dentry->d_inode;
        if (!S_ISDIR(inode->i_mode))
                return -ENOTDIR;
        dn = kmem_cache_alloc(dn_cache, SLAB_KERNEL);
        if (dn == NULL)
                return -ENOMEM;
        write_lock(&dn_lock);
        prev = &inode->i_dnotify;
        while ((odn = *prev) != NULL) {
                if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
                        odn->dn_fd = fd;
                        odn->dn_mask |= arg;
                        inode->i_dnotify_mask |= arg & ~DN_MULTISHOT;
                        goto out_free;
                }
                prev = &odn->dn_next;
        }

        error = f_setown(filp, current->pid, 0);
        if (error)
                goto out_free;

        dn->dn_mask = arg;
        dn->dn_fd = fd;
        dn->dn_filp = filp;
        dn->dn_owner = id;
        inode->i_dnotify_mask |= arg & ~DN_MULTISHOT;
        dn->dn_next = inode->i_dnotify;
        inode->i_dnotify = dn;
out:
        write_unlock(&dn_lock);
        return error;
out_free:
        kmem_cache_free(dn_cache, dn);
        goto out;
}

void __inode_dir_notify(struct inode *inode, unsigned long event)
{
        struct dnotify_struct * dn;
        struct dnotify_struct **prev;
        struct fown_struct *    fown;
        int                     changed = 0;

        write_lock(&dn_lock);
        prev = &inode->i_dnotify;
        while ((dn = *prev) != NULL) {
                if ((dn->dn_mask & event) == 0) {
                        prev = &dn->dn_next;
                        continue;
                }
                fown = &dn->dn_filp->f_owner;
                send_sigio(fown, dn->dn_fd, POLL_MSG);
                if (dn->dn_mask & DN_MULTISHOT)
                        prev = &dn->dn_next;
                else {
                        *prev = dn->dn_next;
                        changed = 1;
                        kmem_cache_free(dn_cache, dn);
                }
        }
        if (changed)
                redo_inode_mask(inode);
        write_unlock(&dn_lock);
}

EXPORT_SYMBOL(__inode_dir_notify);

/*
 * This is hopelessly wrong, but unfixable without API changes.  At
 * least it doesn't oops the kernel...
 *
 * To safely access ->d_parent we need to keep d_move away from it.  Use the
 * dentry's d_lock for this.
 */
void dnotify_parent(struct dentry *dentry, unsigned long event)
{
        struct dentry *parent;

        if (!dir_notify_enable)
                return;

        spin_lock(&dentry->d_lock);
        parent = dentry->d_parent;
        if (parent->d_inode->i_dnotify_mask & event) {
                dget(parent);
                spin_unlock(&dentry->d_lock);
                __inode_dir_notify(parent->d_inode, event);
                dput(parent);
        } else {
                spin_unlock(&dentry->d_lock);
        }
}
EXPORT_SYMBOL_GPL(dnotify_parent);

static int __init dnotify_init(void)
{
        dn_cache = kmem_cache_create("dnotify_cache",
                sizeof(struct dnotify_struct), 0, SLAB_PANIC, NULL, NULL);
        return 0;
}

module_init(dnotify_init)