FreeBSD/Linux Kernel Cross Reference
sys/fs/inotify_user.c

     /*
      * 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 <linux/magic.h>
    
    #include <asm/ioctls.h>
    
    static struct kmem_cache *watch_cachep __read_mostly;
    static struct kmem_cache *event_cachep __read_mostly;
    
    static struct vfsmount *inotify_mnt __read_mostly;
    
    /* these are configurable via /proc/sys/fs/inotify/ */
    static int inotify_max_user_instances __read_mostly;
    static int inotify_max_user_watches __read_mostly;
    static 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 */
            struct fasync_struct    *fa;            /* async notification */
            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_NOFS);
           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_get_last_event - return the last event in the given dev's queue
    *
    * Caller must hold dev->ev_mutex.
    */
   static inline struct inotify_kernel_event *
   inotify_dev_get_last_event(struct inotify_device *dev)
   {
           if (list_empty(&dev->events))
                   return NULL;
           return list_entry(dev->events.prev, 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 inode *ignored)
   {
           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 || w->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_last_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);
           kill_fasync(&dev->fa, SIGIO, POLL_IN);
   
   out:
           mutex_unlock(&dev->ev_mutex);
   }
   
   /*
    * remove_kevent - cleans up 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;
   }
   
   /*
    * free_kevent - frees the given kevent.
    */
   static void free_kevent(struct inotify_kernel_event *kevent)
   {
           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);
                   free_kevent(kevent);
           }
   }
   
   /*
    * find_inode - resolve a user-given path to a specific inode
    */
   static int find_inode(const char __user *dirname, struct path *path,
                         unsigned flags)
   {
           int error;
   
           error = user_path_at(AT_FDCWD, dirname, flags, path);
           if (error)
                   return error;
           /* you can only watch an inode if you have read permissions on it */
           error = inode_permission(path->dentry->d_inode, MAY_READ);
           if (error)
                   path_put(path);
           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);
   
           inotify_init_watch(&watch->wdata);
           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) {
   
                   prepare_to_wait(&dev->wq, &wait, TASK_INTERRUPTIBLE);
   
                   mutex_lock(&dev->ev_mutex);
                   if (!list_empty(&dev->events)) {
                           ret = 0;
                           break;
                   }
                   mutex_unlock(&dev->ev_mutex);
   
                   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;
   
           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) {
                           if (ret == 0 && count > 0) {
                                   /*
                                    * could not get a single event because we
                                    * didn't have enough buffer space.
                                    */
                                   ret = -EINVAL;
                           }
                           break;
                   }
                   remove_kevent(dev, kevent);
   
                   /*
                    * Must perform the copy_to_user outside the mutex in order
                    * to avoid a lock order reversal with mmap_sem.
                    */
                   mutex_unlock(&dev->ev_mutex);
   
                   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;
                   }
   
                   free_kevent(kevent);
   
                   mutex_lock(&dev->ev_mutex);
           }
           mutex_unlock(&dev->ev_mutex);
   
           return ret;
   }
   
   static int inotify_fasync(int fd, struct file *file, int on)
   {
           struct inotify_device *dev = file->private_data;
   
           return fasync_helper(fd, file, on, &dev->fa) >= 0 ? 0 : -EIO;
   }
   
   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,
           .fasync         = inotify_fasync,
           .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_init1(int flags)
   {
           struct inotify_device *dev;
           struct inotify_handle *ih;
           struct user_struct *user;
           struct file *filp;
           int fd, ret;
   
           /* Check the IN_* constants for consistency.  */
           BUILD_BUG_ON(IN_CLOEXEC != O_CLOEXEC);
           BUILD_BUG_ON(IN_NONBLOCK != O_NONBLOCK);
   
           if (flags & ~(IN_CLOEXEC | IN_NONBLOCK))
                   return -EINVAL;
   
           fd = get_unused_fd_flags(flags & O_CLOEXEC);
           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 (IS_ERR(ih)) {
                   ret = PTR_ERR(ih);
                   goto out_free_dev;
           }
           dev->ih = ih;
           dev->fa = NULL;
   
           filp->f_op = &inotify_fops;
           filp->f_path.mnt = mntget(inotify_mnt);
           filp->f_path.dentry = dget(inotify_mnt->mnt_root);
           filp->f_mapping = filp->f_path.dentry->d_inode->i_mapping;
           filp->f_mode = FMODE_READ;
           filp->f_flags = O_RDONLY | (flags & O_NONBLOCK);
           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_init(void)
   {
           return sys_inotify_init1(0);
   }
   
   asmlinkage long sys_inotify_add_watch(int fd, const char __user *pathname, u32 mask)
   {
           struct inode *inode;
           struct inotify_device *dev;
           struct path path;
           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(pathname, &path, flags);
           if (unlikely(ret))
                   goto fput_and_out;
   
           /* inode held in place by reference to path; dev by fget on fd */
           inode = path.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_put(&path);
   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 int
   inotify_get_sb(struct file_system_type *fs_type, int flags,
                  const char *dev_name, void *data, struct vfsmount *mnt)
   {
           return get_sb_pseudo(fs_type, "inotify", NULL,
                           INOTIFYFS_SUPER_MAGIC, mnt);
   }
   
   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);
           event_cachep = kmem_cache_create("inotify_event_cache",
                                            sizeof(struct inotify_kernel_event),
                                            0, SLAB_PANIC, NULL);
   
           return 0;
   }
   
   module_init(inotify_user_setup);

Cache object: d43e804f1c34e999deed1aa85559f33c