cregit-Linux how code gets into the kernel

Release 4.10 fs/notify/notification.c

Directory: fs/notify
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <>
 *  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
 *  GNU General Public License for more details.
 *  You should have received a copy of the GNU General Public License
 *  along with this program; see the file COPYING.  If not, write to
 *  the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.

 * Basic idea behind the notification queue: An fsnotify group (like inotify)
 * sends the userspace notification about events asynchronously some time after
 * the event happened.  When inotify gets an event it will need to add that
 * event to the group notify queue.  Since a single event might need to be on
 * multiple group's notification queues we can't add the event directly to each
 * queue and instead add a small "event_holder" to each queue.  This event_holder
 * has a pointer back to the original event.  Since the majority of events are
 * going to end up on one, and only one, notification queue we embed one
 * event_holder into each event.  This means we have a single allocation instead
 * of always needing two.  If the embedded event_holder is already in use by
 * another group a new event_holder (from fsnotify_event_holder_cachep) will be
 * allocated and used.

#include <linux/fs.h>
#include <linux/init.h>
#include <linux/kernel.h>
#include <linux/list.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/mutex.h>
#include <linux/namei.h>
#include <linux/path.h>
#include <linux/slab.h>
#include <linux/spinlock.h>

#include <linux/atomic.h>

#include <linux/fsnotify_backend.h>
#include "fsnotify.h"

static atomic_t fsnotify_sync_cookie = ATOMIC_INIT(0);

 * fsnotify_get_cookie - return a unique cookie for use in synchronizing events.
 * Called from fsnotify_move, which is inlined into filesystem modules.

u32 fsnotify_get_cookie(void) { return atomic_inc_return(&fsnotify_sync_cookie); }


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EXPORT_SYMBOL_GPL(fsnotify_get_cookie); /* return true if the notify queue is empty, false otherwise */
bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group) { assert_spin_locked(&group->notification_lock); return list_empty(&group->notification_list) ? true : false; }


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void fsnotify_destroy_event(struct fsnotify_group *group, struct fsnotify_event *event) { /* Overflow events are per-group and we don't want to free them */ if (!event || event->mask == FS_Q_OVERFLOW) return; /* * If the event is still queued, we have a problem... Do an unreliable * lockless check first to avoid locking in the common case. The * locking may be necessary for permission events which got removed * from the list by a different CPU than the one freeing the event. */ if (!list_empty(&event->list)) { spin_lock(&group->notification_lock); WARN_ON(!list_empty(&event->list)); spin_unlock(&group->notification_lock); } group->ops->free_event(event); }


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/* * Add an event to the group notification queue. The group can later pull this * event off the queue to deal with. The function returns 0 if the event was * added to the queue, 1 if the event was merged with some other queued event, * 2 if the event was not queued - either the queue of events has overflown * or the group is shutting down. */
int fsnotify_add_event(struct fsnotify_group *group, struct fsnotify_event *event, int (*merge)(struct list_head *, struct fsnotify_event *)) { int ret = 0; struct list_head *list = &group->notification_list; pr_debug("%s: group=%p event=%p\n", __func__, group, event); spin_lock(&group->notification_lock); if (group->shutdown) { spin_unlock(&group->notification_lock); return 2; } if (group->q_len >= group->max_events) { ret = 2; /* Queue overflow event only if it isn't already queued */ if (!list_empty(&group->overflow_event->list)) { spin_unlock(&group->notification_lock); return ret; } event = group->overflow_event; goto queue; } if (!list_empty(list) && merge) { ret = merge(list, event); if (ret) { spin_unlock(&group->notification_lock); return ret; } } queue: group->q_len++; list_add_tail(&event->list, list); spin_unlock(&group->notification_lock); wake_up(&group->notification_waitq); kill_fasync(&group->fsn_fa, SIGIO, POLL_IN); return ret; }


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/* * Remove and return the first event from the notification list. It is the * responsibility of the caller to destroy the obtained event */
struct fsnotify_event *fsnotify_remove_first_event(struct fsnotify_group *group) { struct fsnotify_event *event; assert_spin_locked(&group->notification_lock); pr_debug("%s: group=%p\n", __func__, group); event = list_first_entry(&group->notification_list, struct fsnotify_event, list); /* * We need to init list head for the case of overflow event so that * check in fsnotify_add_event() works */ list_del_init(&event->list); group->q_len--; return event; }


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/* * This will not remove the event, that must be done with * fsnotify_remove_first_event() */
struct fsnotify_event *fsnotify_peek_first_event(struct fsnotify_group *group) { assert_spin_locked(&group->notification_lock); return list_first_entry(&group->notification_list, struct fsnotify_event, list); }


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/* * Called when a group is being torn down to clean up any outstanding * event notifications. */
void fsnotify_flush_notify(struct fsnotify_group *group) { struct fsnotify_event *event; spin_lock(&group->notification_lock); while (!fsnotify_notify_queue_is_empty(group)) { event = fsnotify_remove_first_event(group); spin_unlock(&group->notification_lock); fsnotify_destroy_event(group, event); spin_lock(&group->notification_lock); } spin_unlock(&group->notification_lock); }


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/* * fsnotify_create_event - Allocate a new event which will be sent to each * group's handle_event function if the group was interested in this * particular event. * * @inode the inode which is supposed to receive the event (sometimes a * parent of the inode to which the event happened. * @mask what actually happened. * @data pointer to the object which was actually affected * @data_type flag indication if the data is a file, path, inode, nothing... * @name the filename, if available */
void fsnotify_init_event(struct fsnotify_event *event, struct inode *inode, u32 mask) { INIT_LIST_HEAD(&event->list); event->inode = inode; event->mask = mask; }


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Overall Contributors

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Directory: fs/notify
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