linux/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>
#include <linux/fdtable.h>

int dir_notify_enable __read_mostly = 1;

static struct kmem_cache *dn_cache __read_mostly;

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_path.dentry->d_inode;
	if (!S_ISDIR(inode->i_mode))
		return;
	spin_lock(&inode->i_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;
	}
	spin_unlock(&inode->i_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;
	struct file *f;
	int error = 0;

	if ((arg & ~DN_MULTISHOT) == 0) {
		dnotify_flush(filp, id);
		return 0;
	}
	if (!dir_notify_enable)
		return -EINVAL;
	inode = filp->f_path.dentry->d_inode;
	if (!S_ISDIR(inode->i_mode))
		return -ENOTDIR;
	dn = kmem_cache_alloc(dn_cache, GFP_KERNEL);
	if (dn == NULL)
		return -ENOMEM;
	spin_lock(&inode->i_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;
	}

	rcu_read_lock();
	f = fcheck(fd);
	rcu_read_unlock();
	/* we'd lost the race with close(), sod off silently */
	/* note that inode->i_lock prevents reordering problems
	 * between accesses to descriptor table and ->i_dnotify */
	if (f != filp)
		goto out_free;

	error = __f_setown(filp, task_pid(current), PIDTYPE_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;
	spin_unlock(&inode->i_lock);

	if (filp->f_op && filp->f_op->dir_notify)
		return filp->f_op->dir_notify(filp, arg);
	return 0;

out_free:
	spin_unlock(&inode->i_lock);
	kmem_cache_free(dn_cache, dn);
	return error;
}

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;

	spin_lock(&inode->i_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);
	spin_unlock(&inode->i_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);
	return 0;
}

module_init(dnotify_init)