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/init.h>
  22 #include <linux/module.h>
  23 #include <linux/srcu.h>
  24
  25 #include <linux/fsnotify_backend.h>
  26 #include "fsnotify.h"
  27
  28 /*
  29  * Clear all of the marks on an inode when it is being evicted from core
  30  */
  31 void __fsnotify_inode_delete(struct inode *inode)
  32 {
  33         fsnotify_clear_marks_by_inode(inode);
  34 }
  35 EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
  36
  37 /*
  38  * Given an inode, first check if we care what happens to our children.  Inotify
  39  * and dnotify both tell their parents about events.  If we care about any event
  40  * on a child we run all of our children and set a dentry flag saying that the
  41  * parent cares.  Thus when an event happens on a child it can quickly tell if
  42  * if there is a need to find a parent and send the event to the parent.
  43  */
  44 void __fsnotify_update_child_dentry_flags(struct inode *inode)
  45 {
  46         struct dentry *alias;
  47         int watched;
  48
  49         if (!S_ISDIR(inode->i_mode))
  50                 return;
  51
  52         /* determine if the children should tell inode about their events */
  53         watched = fsnotify_inode_watches_children(inode);
  54
  55         spin_lock(&dcache_lock);
  56         /* run all of the dentries associated with this inode.  Since this is a
  57          * directory, there damn well better only be one item on this list */
  58         list_for_each_entry(alias, &inode->i_dentry, d_alias) {
  59                 struct dentry *child;
  60
  61                 /* run all of the children of the original inode and fix their
  62                  * d_flags to indicate parental interest (their parent is the
  63                  * original inode) */
  64                 list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
  65                         if (!child->d_inode)
  66                                 continue;
  67
  68                         spin_lock(&child->d_lock);
  69                         if (watched)
  70                                 child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
  71                         else
  72                                 child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
  73                         spin_unlock(&child->d_lock);
  74                 }
  75         }
  76         spin_unlock(&dcache_lock);
  77 }
  78
  79 /* Notify this dentry's parent about a child's events. */
  80 void __fsnotify_parent(struct dentry *dentry, __u32 mask)
  81 {
  82         struct dentry *parent;
  83         struct inode *p_inode;
  84         bool send = false;
  85         bool should_update_children = false;
  86
  87         if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
  88                 return;
  89
  90         spin_lock(&dentry->d_lock);
  91         parent = dentry->d_parent;
  92         p_inode = parent->d_inode;
  93
  94         if (fsnotify_inode_watches_children(p_inode)) {
  95                 if (p_inode->i_fsnotify_mask & mask) {
  96                         dget(parent);
  97                         send = true;
  98                 }
  99         } else {
 100                 /*
 101                  * The parent doesn't care about events on it's children but
 102                  * at least one child thought it did.  We need to run all the
 103                  * children and update their d_flags to let them know p_inode
 104                  * doesn't care about them any more.
 105                  */
 106                 dget(parent);
 107                 should_update_children = true;
 108         }
 109
 110         spin_unlock(&dentry->d_lock);
 111
 112         if (send) {
 113                 /* we are notifying a parent so come up with the new mask which
 114                  * specifies these are events which came from a child. */
 115                 mask |= FS_EVENT_ON_CHILD;
 116
 117                 fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
 118                          dentry->d_name.name, 0);
 119                 dput(parent);
 120         }
 121
 122         if (unlikely(should_update_children)) {
 123                 __fsnotify_update_child_dentry_flags(p_inode);
 124                 dput(parent);
 125         }
 126 }
 127 EXPORT_SYMBOL_GPL(__fsnotify_parent);
 128
 129 /*
 130  * This is the main call to fsnotify.  The VFS calls into hook specific functions
 131  * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
 132  * out to all of the registered fsnotify_group.  Those groups can then use the
 133  * notification event in whatever means they feel necessary.
 134  */
 135 void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is, const char *file_name, u32 cookie)
 136 {
 137         struct fsnotify_group *group;
 138         struct fsnotify_event *event = NULL;
 139         int idx;
 140         /* global tests shouldn't care about events on child only the specific event */
 141         __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
 142
 143         if (list_empty(&fsnotify_groups))
 144                 return;
 145
 146         if (!(test_mask & fsnotify_mask))
 147                 return;
 148
 149         if (!(test_mask & to_tell->i_fsnotify_mask))
 150                 return;
 151         /*
 152          * SRCU!!  the groups list is very very much read only and the path is
 153          * very hot.  The VAST majority of events are not going to need to do
 154          * anything other than walk the list so it's crazy to pre-allocate.
 155          */
 156         idx = srcu_read_lock(&fsnotify_grp_srcu);
 157         list_for_each_entry_rcu(group, &fsnotify_groups, group_list) {
 158                 if (test_mask & group->mask) {
 159                         if (!group->ops->should_send_event(group, to_tell, mask))
 160                                 continue;
 161                         if (!event) {
 162                                 event = fsnotify_create_event(to_tell, mask, data,
 163                                                               data_is, file_name, cookie,
 164                                                               GFP_KERNEL);
 165                                 /* shit, we OOM'd and now we can't tell, maybe
 166                                  * someday someone else will want to do something
 167                                  * here */
 168                                 if (!event)
 169                                         break;
 170                         }
 171                         group->ops->handle_event(group, event);
 172                 }
 173         }
 174         srcu_read_unlock(&fsnotify_grp_srcu, idx);
 175         /*
 176          * fsnotify_create_event() took a reference so the event can't be cleaned
 177          * up while we are still trying to add it to lists, drop that one.
 178          */
 179         if (event)
 180                 fsnotify_put_event(event);
 181 }
 182 EXPORT_SYMBOL_GPL(fsnotify);
 183
 184 static __init int fsnotify_init(void)
 185 {
 186         return init_srcu_struct(&fsnotify_grp_srcu);
 187 }
 188 subsys_initcall(fsnotify_init);