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[PATCH] inotify (1/5): split kernel API from userspace support

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The following series of patches introduces a kernel API for inotify,
making it possible for kernel modules to benefit from inotify's
mechanism for watching inodes.  With these patches, inotify will
maintain for each caller a list of watches (via an embedded struct
inotify_watch), where each inotify_watch is associated with a
corresponding struct inode.  The caller registers an event handler and
specifies for which filesystem events their event handler should be
called per inotify_watch.

Signed-off-by: Amy Griffis <amy.griffis@hp.com>
Acked-by: Robert Love <rml@novell.com>
Acked-by: John McCutchan <john@johnmccutchan.com>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
This commit is contained in:
Amy Griffis
2006-06-01 13:10:59 -07:00
committed by Al Viro
parent 90204e0b7b
commit 2d9048e201
8 changed files with 1066 additions and 741 deletions
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717
fs/inotify_user.c Normal file
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/*
* fs/inotify_user.c - inotify support for userspace
*
* Authors:
* John McCutchan <ttb@tentacle.dhs.org>
* Robert Love <rml@novell.com>
*
* Copyright (C) 2005 John McCutchan
* Copyright 2006 Hewlett-Packard Development Company, L.P.
*
* 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/kernel.h>
#include <linux/sched.h>
#include <linux/slab.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/mount.h>
#include <linux/namei.h>
#include <linux/poll.h>
#include <linux/init.h>
#include <linux/list.h>
#include <linux/inotify.h>
#include <linux/syscalls.h>
#include <asm/ioctls.h>
static kmem_cache_t *watch_cachep __read_mostly;
static kmem_cache_t *event_cachep __read_mostly;
static struct vfsmount *inotify_mnt __read_mostly;
/* these are configurable via /proc/sys/fs/inotify/ */
int inotify_max_user_instances __read_mostly;
int inotify_max_user_watches __read_mostly;
int inotify_max_queued_events __read_mostly;
/*
* Lock ordering:
*
* inotify_dev->up_mutex (ensures we don't re-add the same watch)
* inode->inotify_mutex (protects inode's watch list)
* inotify_handle->mutex (protects inotify_handle's watch list)
* inotify_dev->ev_mutex (protects device's event queue)
*/
/*
* Lifetimes of the main data structures:
*
* inotify_device: Lifetime is managed by reference count, from
* sys_inotify_init() until release. Additional references can bump the count
* via get_inotify_dev() and drop the count via put_inotify_dev().
*
* inotify_user_watch: Lifetime is from create_watch() to the receipt of an
* IN_IGNORED event from inotify, or when using IN_ONESHOT, to receipt of the
* first event, or to inotify_destroy().
*/
/*
* struct inotify_device - represents an inotify instance
*
* This structure is protected by the mutex 'mutex'.
*/
struct inotify_device {
wait_queue_head_t wq; /* wait queue for i/o */
struct mutex ev_mutex; /* protects event queue */
struct mutex up_mutex; /* synchronizes watch updates */
struct list_head events; /* list of queued events */
atomic_t count; /* reference count */
struct user_struct *user; /* user who opened this dev */
struct inotify_handle *ih; /* inotify handle */
unsigned int queue_size; /* size of the queue (bytes) */
unsigned int event_count; /* number of pending events */
unsigned int max_events; /* maximum number of events */
};
/*
* struct inotify_kernel_event - An inotify event, originating from a watch and
* queued for user-space. A list of these is attached to each instance of the
* device. In read(), this list is walked and all events that can fit in the
* buffer are returned.
*
* Protected by dev->ev_mutex of the device in which we are queued.
*/
struct inotify_kernel_event {
struct inotify_event event; /* the user-space event */
struct list_head list; /* entry in inotify_device's list */
char *name; /* filename, if any */
};
/*
* struct inotify_user_watch - our version of an inotify_watch, we add
* a reference to the associated inotify_device.
*/
struct inotify_user_watch {
struct inotify_device *dev; /* associated device */
struct inotify_watch wdata; /* inotify watch data */
};
#ifdef CONFIG_SYSCTL
#include <linux/sysctl.h>
static int zero;
ctl_table inotify_table[] = {
{
.ctl_name = INOTIFY_MAX_USER_INSTANCES,
.procname = "max_user_instances",
.data = &inotify_max_user_instances,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &zero,
},
{
.ctl_name = INOTIFY_MAX_USER_WATCHES,
.procname = "max_user_watches",
.data = &inotify_max_user_watches,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &zero,
},
{
.ctl_name = INOTIFY_MAX_QUEUED_EVENTS,
.procname = "max_queued_events",
.data = &inotify_max_queued_events,
.maxlen = sizeof(int),
.mode = 0644,
.proc_handler = &proc_dointvec_minmax,
.strategy = &sysctl_intvec,
.extra1 = &zero
},
{ .ctl_name = 0 }
};
#endif /* CONFIG_SYSCTL */
static inline void get_inotify_dev(struct inotify_device *dev)
{
atomic_inc(&dev->count);
}
static inline void put_inotify_dev(struct inotify_device *dev)
{
if (atomic_dec_and_test(&dev->count)) {
atomic_dec(&dev->user->inotify_devs);
free_uid(dev->user);
kfree(dev);
}
}
/*
* free_inotify_user_watch - cleans up the watch and its references
*/
static void free_inotify_user_watch(struct inotify_watch *w)
{
struct inotify_user_watch *watch;
struct inotify_device *dev;
watch = container_of(w, struct inotify_user_watch, wdata);
dev = watch->dev;
atomic_dec(&dev->user->inotify_watches);
put_inotify_dev(dev);
kmem_cache_free(watch_cachep, watch);
}
/*
* kernel_event - create a new kernel event with the given parameters
*
* This function can sleep.
*/
static struct inotify_kernel_event * kernel_event(s32 wd, u32 mask, u32 cookie,
const char *name)
{
struct inotify_kernel_event *kevent;
kevent = kmem_cache_alloc(event_cachep, GFP_KERNEL);
if (unlikely(!kevent))
return NULL;
/* we hand this out to user-space, so zero it just in case */
memset(&kevent->event, 0, sizeof(struct inotify_event));
kevent->event.wd = wd;
kevent->event.mask = mask;
kevent->event.cookie = cookie;
INIT_LIST_HEAD(&kevent->list);
if (name) {
size_t len, rem, event_size = sizeof(struct inotify_event);
/*
* We need to pad the filename so as to properly align an
* array of inotify_event structures. Because the structure is
* small and the common case is a small filename, we just round
* up to the next multiple of the structure's sizeof. This is
* simple and safe for all architectures.
*/
len = strlen(name) + 1;
rem = event_size - len;
if (len > event_size) {
rem = event_size - (len % event_size);
if (len % event_size == 0)
rem = 0;
}
kevent->name = kmalloc(len + rem, GFP_KERNEL);
if (unlikely(!kevent->name)) {
kmem_cache_free(event_cachep, kevent);
return NULL;
}
memcpy(kevent->name, name, len);
if (rem)
memset(kevent->name + len, 0, rem);
kevent->event.len = len + rem;
} else {
kevent->event.len = 0;
kevent->name = NULL;
}
return kevent;
}
/*
* inotify_dev_get_event - return the next event in the given dev's queue
*
* Caller must hold dev->ev_mutex.
*/
static inline struct inotify_kernel_event *
inotify_dev_get_event(struct inotify_device *dev)
{
return list_entry(dev->events.next, struct inotify_kernel_event, list);
}
/*
* inotify_dev_queue_event - event handler registered with core inotify, adds
* a new event to the given device
*
* Can sleep (calls kernel_event()).
*/
static void inotify_dev_queue_event(struct inotify_watch *w, u32 wd, u32 mask,
u32 cookie, const char *name)
{
struct inotify_user_watch *watch;
struct inotify_device *dev;
struct inotify_kernel_event *kevent, *last;
watch = container_of(w, struct inotify_user_watch, wdata);
dev = watch->dev;
mutex_lock(&dev->ev_mutex);
/* we can safely put the watch as we don't reference it while
* generating the event
*/
if (mask & IN_IGNORED || mask & IN_ONESHOT)
put_inotify_watch(w); /* final put */
/* coalescing: drop this event if it is a dupe of the previous */
last = inotify_dev_get_event(dev);
if (last && last->event.mask == mask && last->event.wd == wd &&
last->event.cookie == cookie) {
const char *lastname = last->name;
if (!name && !lastname)
goto out;
if (name && lastname && !strcmp(lastname, name))
goto out;
}
/* the queue overflowed and we already sent the Q_OVERFLOW event */
if (unlikely(dev->event_count > dev->max_events))
goto out;
/* if the queue overflows, we need to notify user space */
if (unlikely(dev->event_count == dev->max_events))
kevent = kernel_event(-1, IN_Q_OVERFLOW, cookie, NULL);
else
kevent = kernel_event(wd, mask, cookie, name);
if (unlikely(!kevent))
goto out;
/* queue the event and wake up anyone waiting */
dev->event_count++;
dev->queue_size += sizeof(struct inotify_event) + kevent->event.len;
list_add_tail(&kevent->list, &dev->events);
wake_up_interruptible(&dev->wq);
out:
mutex_unlock(&dev->ev_mutex);
}
/*
* remove_kevent - cleans up and ultimately frees the given kevent
*
* Caller must hold dev->ev_mutex.
*/
static void remove_kevent(struct inotify_device *dev,
struct inotify_kernel_event *kevent)
{
list_del(&kevent->list);
dev->event_count--;
dev->queue_size -= sizeof(struct inotify_event) + kevent->event.len;
kfree(kevent->name);
kmem_cache_free(event_cachep, kevent);
}
/*
* inotify_dev_event_dequeue - destroy an event on the given device
*
* Caller must hold dev->ev_mutex.
*/
static void inotify_dev_event_dequeue(struct inotify_device *dev)
{
if (!list_empty(&dev->events)) {
struct inotify_kernel_event *kevent;
kevent = inotify_dev_get_event(dev);
remove_kevent(dev, kevent);
}
}
/*
* find_inode - resolve a user-given path to a specific inode and return a nd
*/
static int find_inode(const char __user *dirname, struct nameidata *nd,
unsigned flags)
{
int error;
error = __user_walk(dirname, flags, nd);
if (error)
return error;
/* you can only watch an inode if you have read permissions on it */
error = vfs_permission(nd, MAY_READ);
if (error)
path_release(nd);
return error;
}
/*
* create_watch - creates a watch on the given device.
*
* Callers must hold dev->up_mutex.
*/
static int create_watch(struct inotify_device *dev, struct inode *inode,
u32 mask)
{
struct inotify_user_watch *watch;
int ret;
if (atomic_read(&dev->user->inotify_watches) >=
inotify_max_user_watches)
return -ENOSPC;
watch = kmem_cache_alloc(watch_cachep, GFP_KERNEL);
if (unlikely(!watch))
return -ENOMEM;
/* save a reference to device and bump the count to make it official */
get_inotify_dev(dev);
watch->dev = dev;
atomic_inc(&dev->user->inotify_watches);
ret = inotify_add_watch(dev->ih, &watch->wdata, inode, mask);
if (ret < 0)
free_inotify_user_watch(&watch->wdata);
return ret;
}
/* Device Interface */
static unsigned int inotify_poll(struct file *file, poll_table *wait)
{
struct inotify_device *dev = file->private_data;
int ret = 0;
poll_wait(file, &dev->wq, wait);
mutex_lock(&dev->ev_mutex);
if (!list_empty(&dev->events))
ret = POLLIN | POLLRDNORM;
mutex_unlock(&dev->ev_mutex);
return ret;
}
static ssize_t inotify_read(struct file *file, char __user *buf,
size_t count, loff_t *pos)
{
size_t event_size = sizeof (struct inotify_event);
struct inotify_device *dev;
char __user *start;
int ret;
DEFINE_WAIT(wait);
start = buf;
dev = file->private_data;
while (1) {
int events;
prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);
mutex_lock(&dev->ev_mutex);
events = !list_empty(&dev->events);
mutex_unlock(&dev->ev_mutex);
if (events) {
ret = 0;
break;
}
if (file->f_flags & O_NONBLOCK) {
ret = -EAGAIN;
break;
}
if (signal_pending(current)) {
ret = -EINTR;
break;
}
schedule();
}
finish_wait(&dev->wq, &wait);
if (ret)
return ret;
mutex_lock(&dev->ev_mutex);
while (1) {
struct inotify_kernel_event *kevent;
ret = buf - start;
if (list_empty(&dev->events))
break;
kevent = inotify_dev_get_event(dev);
if (event_size + kevent->event.len > count)
break;
if (copy_to_user(buf, &kevent->event, event_size)) {
ret = -EFAULT;
break;
}
buf += event_size;
count -= event_size;
if (kevent->name) {
if (copy_to_user(buf, kevent->name, kevent->event.len)){
ret = -EFAULT;
break;
}
buf += kevent->event.len;
count -= kevent->event.len;
}
remove_kevent(dev, kevent);
}
mutex_unlock(&dev->ev_mutex);
return ret;
}
static int inotify_release(struct inode *ignored, struct file *file)
{
struct inotify_device *dev = file->private_data;
inotify_destroy(dev->ih);
/* destroy all of the events on this device */
mutex_lock(&dev->ev_mutex);
while (!list_empty(&dev->events))
inotify_dev_event_dequeue(dev);
mutex_unlock(&dev->ev_mutex);
/* free this device: the put matching the get in inotify_init() */
put_inotify_dev(dev);
return 0;
}
static long inotify_ioctl(struct file *file, unsigned int cmd,
unsigned long arg)
{
struct inotify_device *dev;
void __user *p;
int ret = -ENOTTY;
dev = file->private_data;
p = (void __user *) arg;
switch (cmd) {
case FIONREAD:
ret = put_user(dev->queue_size, (int __user *) p);
break;
}
return ret;
}
static const struct file_operations inotify_fops = {
.poll = inotify_poll,
.read = inotify_read,
.release = inotify_release,
.unlocked_ioctl = inotify_ioctl,
.compat_ioctl = inotify_ioctl,
};
static const struct inotify_operations inotify_user_ops = {
.handle_event = inotify_dev_queue_event,
.destroy_watch = free_inotify_user_watch,
};
asmlinkage long sys_inotify_init(void)
{
struct inotify_device *dev;
struct inotify_handle *ih;
struct user_struct *user;
struct file *filp;
int fd, ret;
fd = get_unused_fd();
if (fd < 0)
return fd;
filp = get_empty_filp();
if (!filp) {
ret = -ENFILE;
goto out_put_fd;
}
user = get_uid(current->user);
if (unlikely(atomic_read(&user->inotify_devs) >=
inotify_max_user_instances)) {
ret = -EMFILE;
goto out_free_uid;
}
dev = kmalloc(sizeof(struct inotify_device), GFP_KERNEL);
if (unlikely(!dev)) {
ret = -ENOMEM;
goto out_free_uid;
}
ih = inotify_init(&inotify_user_ops);
if (unlikely(IS_ERR(ih))) {
ret = PTR_ERR(ih);
goto out_free_dev;
}
dev->ih = ih;
filp->f_op = &inotify_fops;
filp->f_vfsmnt = mntget(inotify_mnt);
filp->f_dentry = dget(inotify_mnt->mnt_root);
filp->f_mapping = filp->f_dentry->d_inode->i_mapping;
filp->f_mode = FMODE_READ;
filp->f_flags = O_RDONLY;
filp->private_data = dev;
INIT_LIST_HEAD(&dev->events);
init_waitqueue_head(&dev->wq);
mutex_init(&dev->ev_mutex);
mutex_init(&dev->up_mutex);
dev->event_count = 0;
dev->queue_size = 0;
dev->max_events = inotify_max_queued_events;
dev->user = user;
atomic_set(&dev->count, 0);
get_inotify_dev(dev);
atomic_inc(&user->inotify_devs);
fd_install(fd, filp);
return fd;
out_free_dev:
kfree(dev);
out_free_uid:
free_uid(user);
put_filp(filp);
out_put_fd:
put_unused_fd(fd);
return ret;
}
asmlinkage long sys_inotify_add_watch(int fd, const char __user *path, u32 mask)
{
struct inode *inode;
struct inotify_device *dev;
struct nameidata nd;
struct file *filp;
int ret, fput_needed;
unsigned flags = 0;
filp = fget_light(fd, &fput_needed);
if (unlikely(!filp))
return -EBADF;
/* verify that this is indeed an inotify instance */
if (unlikely(filp->f_op != &inotify_fops)) {
ret = -EINVAL;
goto fput_and_out;
}
if (!(mask & IN_DONT_FOLLOW))
flags |= LOOKUP_FOLLOW;
if (mask & IN_ONLYDIR)
flags |= LOOKUP_DIRECTORY;
ret = find_inode(path, &nd, flags);
if (unlikely(ret))
goto fput_and_out;
/* inode held in place by reference to nd; dev by fget on fd */
inode = nd.dentry->d_inode;
dev = filp->private_data;
mutex_lock(&dev->up_mutex);
ret = inotify_find_update_watch(dev->ih, inode, mask);
if (ret == -ENOENT)
ret = create_watch(dev, inode, mask);
mutex_unlock(&dev->up_mutex);
path_release(&nd);
fput_and_out:
fput_light(filp, fput_needed);
return ret;
}
asmlinkage long sys_inotify_rm_watch(int fd, u32 wd)
{
struct file *filp;
struct inotify_device *dev;
int ret, fput_needed;
filp = fget_light(fd, &fput_needed);
if (unlikely(!filp))
return -EBADF;
/* verify that this is indeed an inotify instance */
if (unlikely(filp->f_op != &inotify_fops)) {
ret = -EINVAL;
goto out;
}
dev = filp->private_data;
/* we free our watch data when we get IN_IGNORED */
ret = inotify_rm_wd(dev->ih, wd);
out:
fput_light(filp, fput_needed);
return ret;
}
static struct super_block *
inotify_get_sb(struct file_system_type *fs_type, int flags,
const char *dev_name, void *data)
{
return get_sb_pseudo(fs_type, "inotify", NULL, 0xBAD1DEA);
}
static struct file_system_type inotify_fs_type = {
.name = "inotifyfs",
.get_sb = inotify_get_sb,
.kill_sb = kill_anon_super,
};
/*
* inotify_user_setup - Our initialization function. Note that we cannnot return
* error because we have compiled-in VFS hooks. So an (unlikely) failure here
* must result in panic().
*/
static int __init inotify_user_setup(void)
{
int ret;
ret = register_filesystem(&inotify_fs_type);
if (unlikely(ret))
panic("inotify: register_filesystem returned %d!\n", ret);
inotify_mnt = kern_mount(&inotify_fs_type);
if (IS_ERR(inotify_mnt))
panic("inotify: kern_mount ret %ld!\n", PTR_ERR(inotify_mnt));
inotify_max_queued_events = 16384;
inotify_max_user_instances = 128;
inotify_max_user_watches = 8192;
watch_cachep = kmem_cache_create("inotify_watch_cache",
sizeof(struct inotify_user_watch),
0, SLAB_PANIC, NULL, NULL);
event_cachep = kmem_cache_create("inotify_event_cache",
sizeof(struct inotify_kernel_event),
0, SLAB_PANIC, NULL, NULL);
return 0;
}
module_init(inotify_user_setup);