Root/fs/notify/fsnotify.c

1/*
2 * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
3 *
4 * This program is free software; you can redistribute it and/or modify
5 * it under the terms of the GNU General Public License as published by
6 * the Free Software Foundation; either version 2, or (at your option)
7 * any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; see the file COPYING. If not, write to
16 * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
17 */
18
19#include <linux/dcache.h>
20#include <linux/fs.h>
21#include <linux/gfp.h>
22#include <linux/init.h>
23#include <linux/module.h>
24#include <linux/srcu.h>
25
26#include <linux/fsnotify_backend.h>
27#include "fsnotify.h"
28
29/*
30 * Clear all of the marks on an inode when it is being evicted from core
31 */
32void __fsnotify_inode_delete(struct inode *inode)
33{
34    fsnotify_clear_marks_by_inode(inode);
35}
36EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
37
38/*
39 * Given an inode, first check if we care what happens to our children. Inotify
40 * and dnotify both tell their parents about events. If we care about any event
41 * on a child we run all of our children and set a dentry flag saying that the
42 * parent cares. Thus when an event happens on a child it can quickly tell if
43 * if there is a need to find a parent and send the event to the parent.
44 */
45void __fsnotify_update_child_dentry_flags(struct inode *inode)
46{
47    struct dentry *alias;
48    int watched;
49
50    if (!S_ISDIR(inode->i_mode))
51        return;
52
53    /* determine if the children should tell inode about their events */
54    watched = fsnotify_inode_watches_children(inode);
55
56    spin_lock(&dcache_lock);
57    /* run all of the dentries associated with this inode. Since this is a
58     * directory, there damn well better only be one item on this list */
59    list_for_each_entry(alias, &inode->i_dentry, d_alias) {
60        struct dentry *child;
61
62        /* run all of the children of the original inode and fix their
63         * d_flags to indicate parental interest (their parent is the
64         * original inode) */
65        list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
66            if (!child->d_inode)
67                continue;
68
69            spin_lock(&child->d_lock);
70            if (watched)
71                child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
72            else
73                child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
74            spin_unlock(&child->d_lock);
75        }
76    }
77    spin_unlock(&dcache_lock);
78}
79
80/* Notify this dentry's parent about a child's events. */
81void __fsnotify_parent(struct dentry *dentry, __u32 mask)
82{
83    struct dentry *parent;
84    struct inode *p_inode;
85    bool send = false;
86    bool should_update_children = false;
87
88    if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
89        return;
90
91    spin_lock(&dentry->d_lock);
92    parent = dentry->d_parent;
93    p_inode = parent->d_inode;
94
95    if (fsnotify_inode_watches_children(p_inode)) {
96        if (p_inode->i_fsnotify_mask & mask) {
97            dget(parent);
98            send = true;
99        }
100    } else {
101        /*
102         * The parent doesn't care about events on it's children but
103         * at least one child thought it did. We need to run all the
104         * children and update their d_flags to let them know p_inode
105         * doesn't care about them any more.
106         */
107        dget(parent);
108        should_update_children = true;
109    }
110
111    spin_unlock(&dentry->d_lock);
112
113    if (send) {
114        /* we are notifying a parent so come up with the new mask which
115         * specifies these are events which came from a child. */
116        mask |= FS_EVENT_ON_CHILD;
117
118        fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
119             dentry->d_name.name, 0);
120        dput(parent);
121    }
122
123    if (unlikely(should_update_children)) {
124        __fsnotify_update_child_dentry_flags(p_inode);
125        dput(parent);
126    }
127}
128EXPORT_SYMBOL_GPL(__fsnotify_parent);
129
130/*
131 * This is the main call to fsnotify. The VFS calls into hook specific functions
132 * in linux/fsnotify.h. Those functions then in turn call here. Here will call
133 * out to all of the registered fsnotify_group. Those groups can then use the
134 * notification event in whatever means they feel necessary.
135 */
136void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const char *file_name, u32 cookie)
137{
138    struct fsnotify_group *group;
139    struct fsnotify_event *event = NULL;
140    int idx;
141    /* global tests shouldn't care about events on child only the specific event */
142    __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
143
144    if (list_empty(&fsnotify_groups))
145        return;
146
147    if (!(test_mask & fsnotify_mask))
148        return;
149
150    if (!(test_mask & to_tell->i_fsnotify_mask))
151        return;
152    /*
153     * SRCU!! the groups list is very very much read only and the path is
154     * very hot. The VAST majority of events are not going to need to do
155     * anything other than walk the list so it's crazy to pre-allocate.
156     */
157    idx = srcu_read_lock(&fsnotify_grp_srcu);
158    list_for_each_entry_rcu(group, &fsnotify_groups, group_list) {
159        if (test_mask & group->mask) {
160            if (!group->ops->should_send_event(group, to_tell, mask))
161                continue;
162            if (!event) {
163                event = fsnotify_create_event(to_tell, mask, data,
164                                  data_is, file_name, cookie,
165                                  GFP_KERNEL);
166                /* shit, we OOM'd and now we can't tell, maybe
167                 * someday someone else will want to do something
168                 * here */
169                if (!event)
170                    break;
171            }
172            group->ops->handle_event(group, event);
173        }
174    }
175    srcu_read_unlock(&fsnotify_grp_srcu, idx);
176    /*
177     * fsnotify_create_event() took a reference so the event can't be cleaned
178     * up while we are still trying to add it to lists, drop that one.
179     */
180    if (event)
181        fsnotify_put_event(event);
182}
183EXPORT_SYMBOL_GPL(fsnotify);
184
185static __init int fsnotify_init(void)
186{
187    return init_srcu_struct(&fsnotify_grp_srcu);
188}
189subsys_initcall(fsnotify_init);
190

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