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  */
  32 void __fsnotify_inode_delete(struct inode *inode)
  33 {
  34         fsnotify_clear_marks_by_inode(inode);
  35 }
  36 EXPORT_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  */
  45 void __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. */
  81 void __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 }
 128 EXPORT_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  */
 136 void 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 }
 183 EXPORT_SYMBOL_GPL(fsnotify);
 184
 185 static __init int fsnotify_init(void)
 186 {
 187         return init_srcu_struct(&fsnotify_grp_srcu);
 188 }
 189 subsys_initcall(fsnotify_init);