/*
* Directory notifications for Linux.
*
* Copyright (C) 2000,2001,2002 Stephen Rothwell
*
* Copyright (C) 2009 Eric Paris <Red Hat Inc>
* dnotify was largly rewritten to use the new fsnotify infrastructure
*
* 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>
#include <linux/fsnotify_backend.h>
int dir_notify_enable __read_mostly = 1;
static struct kmem_cache *dnotify_struct_cache __read_mostly;
static struct kmem_cache *dnotify_mark_entry_cache __read_mostly;
static struct fsnotify_group *dnotify_group __read_mostly;
static DEFINE_MUTEX(dnotify_mark_mutex);
/*
* dnotify will attach one of these to each inode (i_fsnotify_mark_entries) which
* is being watched by dnotify. If multiple userspace applications are watching
* the same directory with dnotify their information is chained in dn
*/
struct dnotify_mark_entry {
struct fsnotify_mark_entry fsn_entry;
struct dnotify_struct *dn;
};
/*
* When a process starts or stops watching an inode the set of events which
* dnotify cares about for that inode may change. This function runs the
* list of everything receiving dnotify events about this directory and calculates
* the set of all those events. After it updates what dnotify is interested in
* it calls the fsnotify function so it can update the set of all events relevant
* to this inode.
*/
static void dnotify_recalc_inode_mask(struct fsnotify_mark_entry *entry)
{
__u32 new_mask, old_mask;
struct dnotify_struct *dn;
struct dnotify_mark_entry *dnentry = container_of(entry,
struct dnotify_mark_entry,
fsn_entry);
assert_spin_locked(&entry->lock);
old_mask = entry->mask;
new_mask = 0;
for (dn = dnentry->dn; dn != NULL; dn = dn->dn_next)
new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
entry->mask = new_mask;
if (old_mask == new_mask)
return;
if (entry->inode)
fsnotify_recalc_inode_mask(entry->inode);
}
/*
* Mains fsnotify call where events are delivered to dnotify.
* Find the dnotify mark on the relevant inode, run the list of dnotify structs
* on that mark and determine which of them has expressed interest in receiving
* events of this type. When found send the correct process and signal and
* destroy the dnotify struct if it was not registered to receive multiple
* events.
*/
static int dnotify_handle_event(struct fsnotify_group *group,
struct fsnotify_event *event)
{
struct fsnotify_mark_entry *entry = NULL;
struct dnotify_mark_entry *dnentry;
struct inode *to_tell;
struct dnotify_struct *dn;
struct dnotify_struct **prev;
struct fown_struct *fown;
to_tell = event->to_tell;
spin_lock(&to_tell->i_lock);
entry = fsnotify_find_mark_entry(group, to_tell);
spin_unlock(&to_tell->i_lock);
/* unlikely since we alreay passed dnotify_should_send_event() */
if (unlikely(!entry))
return 0;
dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
spin_lock(&entry->lock);
prev = &dnentry->dn;
while ((dn = *prev) != NULL) {
if ((dn->dn_mask & event->mask) == 0) {
prev = &dn->dn_next;
continue;
}
fown = &dn->dn_filp->f_owner;
send_sigio(fown, dn->dn_fd, POLL_MSG);
if (dn->dn_mask & FS_DN_MULTISHOT)
prev = &dn->dn_next;
else {
*prev = dn->dn_next;
kmem_cache_free(dnotify_struct_cache, dn);
dnotify_recalc_inode_mask(entry);
}
}
spin_unlock(&entry->lock);
fsnotify_put_mark(entry);
return 0;
}
/*
* Given an inode and mask determine if dnotify would be interested in sending
* userspace notification for that pair.
*/
static bool dnotify_should_send_event(struct fsnotify_group *group,
struct inode *inode, __u32 mask)
{
struct fsnotify_mark_entry *entry;
bool send;
/* !dir_notify_enable should never get here, don't waste time checking
if (!dir_notify_enable)
return 0; */
/* not a dir, dnotify doesn't care */
if (!S_ISDIR(inode->i_mode))
return false;
spin_lock(&inode->i_lock);
entry = fsnotify_find_mark_entry(group, inode);
spin_unlock(&inode->i_lock);
/* no mark means no dnotify watch */
if (!entry)
return false;
mask = (mask & ~FS_EVENT_ON_CHILD);
send = (mask & entry->mask);
fsnotify_put_mark(entry); /* matches fsnotify_find_mark_entry */
return send;
}
static void dnotify_free_mark(struct fsnotify_mark_entry *entry)
{
struct dnotify_mark_entry *dnentry = container_of(entry,
struct dnotify_mark_entry,
fsn_entry);
BUG_ON(dnentry->dn);
kmem_cache_free(dnotify_mark_entry_cache, dnentry);
}
static struct fsnotify_ops dnotify_fsnotify_ops = {
.handle_event = dnotify_handle_event,
.should_send_event = dnotify_should_send_event,
.free_group_priv = NULL,
.freeing_mark = NULL,
.free_event_priv = NULL,
};
/*
* Called every time a file is closed. Looks first for a dnotify mark on the
* inode. If one is found run all of the ->dn entries attached to that
* mark for one relevant to this process closing the file and remove that
* dnotify_struct. If that was the last dnotify_struct also remove the
* fsnotify_mark_entry.
*/
void dnotify_flush(struct file *filp, fl_owner_t id)
{
struct fsnotify_mark_entry *entry;
struct dnotify_mark_entry *dnentry;
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);
entry = fsnotify_find_mark_entry(dnotify_group, inode);
spin_unlock(&inode->i_lock);
if (!entry)
return;
dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
mutex_lock(&dnotify_mark_mutex);
spin_lock(&entry->lock);
prev = &dnentry->dn;
while ((dn = *prev) != NULL) {
if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
*prev = dn->dn_next;
kmem_cache_free(dnotify_struct_cache, dn);
dnotify_recalc_inode_mask(entry);
break;
}
prev = &dn->dn_next;
}
spin_unlock(&entry->lock);
/* nothing else could have found us thanks to the dnotify_mark_mutex */
if (dnentry->dn == NULL)
fsnotify_destroy_mark_by_entry(entry);
fsnotify_recalc_group_mask(dnotify_group);
mutex_unlock(&dnotify_mark_mutex);
fsnotify_put_mark(entry);
}
/* this conversion is done only at watch creation */
static __u32 convert_arg(unsigned long arg)
{
__u32 new_mask = FS_EVENT_ON_CHILD;
if (arg & DN_MULTISHOT)
new_mask |= FS_DN_MULTISHOT;
if (arg & DN_DELETE)
new_mask |= (FS_DELETE | FS_MOVED_FROM);
if (arg & DN_MODIFY)
new_mask |= FS_MODIFY;
if (arg & DN_ACCESS)
new_mask |= FS_ACCESS;
if (arg & DN_ATTRIB)
new_mask |= FS_ATTRIB;
if (arg & DN_RENAME)
new_mask |= FS_DN_RENAME;
if (arg & DN_CREATE)
new_mask |= (FS_CREATE | FS_MOVED_TO);
return new_mask;
}
/*
* If multiple processes watch the same inode with dnotify there is only one
* dnotify mark in inode->i_fsnotify_mark_entries but we chain a dnotify_struct
* onto that mark. This function either attaches the new dnotify_struct onto
* that list, or it |= the mask onto an existing dnofiy_struct.
*/
static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark_entry *dnentry,
fl_owner_t id, int fd, struct file *filp, __u32 mask)
{
struct dnotify_struct *odn;
odn = dnentry->dn;
while (odn != NULL) {
/* adding more events to existing dnofiy_struct? */
if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
odn->dn_fd = fd;
odn->dn_mask |= mask;
return -EEXIST;
}
odn = odn->dn_next;
}
dn->dn_mask = mask;
dn->dn_fd = fd;
dn->dn_filp = filp;
dn->dn_owner = id;
dn->dn_next = dnentry->dn;
dnentry->dn = dn;
return 0;
}
/*
* When a process calls fcntl to attach a dnotify watch to a directory it ends
* up here. Allocate both a mark for fsnotify to add and a dnotify_struct to be
* attached to the fsnotify_mark.
*/
int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
{
struct dnotify_mark_entry *new_dnentry, *dnentry;
struct fsnotify_mark_entry *new_entry, *entry;
struct dnotify_struct *dn;
struct inode *inode;
fl_owner_t id = current->files;
struct file *f;
int destroy = 0, error = 0;
__u32 mask;
/* we use these to tell if we need to kfree */
new_entry = NULL;
dn = NULL;
if (!dir_notify_enable) {
error = -EINVAL;
goto out_err;
}
/* a 0 mask means we are explicitly removing the watch */
if ((arg & ~DN_MULTISHOT) == 0) {
dnotify_flush(filp, id);
error = 0;
goto out_err;
}
/* dnotify only works on directories */
inode = filp->f_path.dentry->d_inode;
if (!S_ISDIR(inode->i_mode)) {
error = -ENOTDIR;
goto out_err;
}
/* expect most fcntl to add new rather than augment old */
dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
if (!dn) {
error = -ENOMEM;
goto out_err;
}
/* new fsnotify mark, we expect most fcntl calls to add a new mark */
new_dnentry = kmem_cache_alloc(dnotify_mark_entry_cache, GFP_KERNEL);
if (!new_dnentry) {
error = -ENOMEM;
goto out_err;
}
/* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
mask = convert_arg(arg);
/* set up the new_entry and new_dnentry */
new_entry = &new_dnentry->fsn_entry;
fsnotify_init_mark(new_entry, dnotify_free_mark);
new_entry->mask = mask;
new_dnentry->dn = NULL;
/* this is needed to prevent the fcntl/close race described below */
mutex_lock(&dnotify_mark_mutex);
/* add the new_entry or find an old one. */
spin_lock(&inode->i_lock);
entry = fsnotify_find_mark_entry(dnotify_group, inode);
spin_unlock(&inode->i_lock);
if (entry) {
dnentry = container_of(entry, struct dnotify_mark_entry, fsn_entry);
spin_lock(&entry->lock);
} else {
fsnotify_add_mark(new_entry, dnotify_group, inode);
spin_lock(&new_entry->lock);
entry = new_entry;
dnentry = new_dnentry;
/* we used new_entry, so don't free it */
new_entry = NULL;
}
rcu_read_lock();
f = fcheck(fd);
rcu_read_unlock();
/* if (f != filp) means that we lost a race and another task/thread
* actually closed the fd we are still playing with before we grabbed
* the dnotify_mark_mutex and entry->lock. Since closing the fd is the
* only time we clean up the mark entries we need to get our mark off
* the list. */
if (f != filp) {
/* if we added ourselves, shoot ourselves, it's possible that
* the flush actually did shoot this entry. That's fine too
* since multiple calls to destroy_mark is perfectly safe, if
* we found a dnentry already attached to the inode, just sod
* off silently as the flush at close time dealt with it.
*/
if (dnentry == new_dnentry)
destroy = 1;
goto out;
}
error = __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
if (error) {
/* if we added, we must shoot */
if (dnentry == new_dnentry)
destroy = 1;
goto out;
}
error = attach_dn(dn, dnentry, id, fd, filp, mask);
/* !error means that we attached the dn to the dnentry, so don't free it */
if (!error)
dn = NULL;
/* -EEXIST means that we didn't add this new dn and used an old one.
* that isn't an error (and the unused dn should be freed) */
else if (error == -EEXIST)
error = 0;
dnotify_recalc_inode_mask(entry);
out:
spin_unlock(&entry->lock);
if (destroy)
fsnotify_destroy_mark_by_entry(entry);
fsnotify_recalc_group_mask(dnotify_group);
mutex_unlock(&dnotify_mark_mutex);
fsnotify_put_mark(entry);
out_err:
if (new_entry)
fsnotify_put_mark(new_entry);
if (dn)
kmem_cache_free(dnotify_struct_cache, dn);
return error;
}
static int __init dnotify_init(void)
{
dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
dnotify_mark_entry_cache = KMEM_CACHE(dnotify_mark_entry, SLAB_PANIC);
dnotify_group = fsnotify_obtain_group(DNOTIFY_GROUP_NUM,
0, &dnotify_fsnotify_ops);
if (IS_ERR(dnotify_group))
panic("unable to allocate fsnotify group for dnotify\n");
return 0;
}
module_init(dnotify_init)
