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/mount.h>
  25 #include <linux/srcu.h>
  26
  27 #include <linux/fsnotify_backend.h>
  28 #include "fsnotify.h"
  29
  30 /*
  31  * Clear all of the marks on an inode when it is being evicted from core
  32  */
  33 void __fsnotify_inode_delete(struct inode *inode)
  34 {
  35         fsnotify_clear_marks_by_inode(inode);
  36 }
  37 EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
  38
  39 void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
  40 {
  41         fsnotify_clear_marks_by_mount(mnt);
  42 }
  43
  44 /*
  45  * Given an inode, first check if we care what happens to our children.  Inotify
  46  * and dnotify both tell their parents about events.  If we care about any event
  47  * on a child we run all of our children and set a dentry flag saying that the
  48  * parent cares.  Thus when an event happens on a child it can quickly tell if
  49  * if there is a need to find a parent and send the event to the parent.
  50  */
  51 void __fsnotify_update_child_dentry_flags(struct inode *inode)
  52 {
  53         struct dentry *alias;
  54         int watched;
  55
  56         if (!S_ISDIR(inode->i_mode))
  57                 return;
  58
  59         /* determine if the children should tell inode about their events */
  60         watched = fsnotify_inode_watches_children(inode);
  61
  62         spin_lock(&inode->i_lock);
  63         /* run all of the dentries associated with this inode.  Since this is a
  64          * directory, there damn well better only be one item on this list */
  65         hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
  66                 struct dentry *child;
  67
  68                 /* run all of the children of the original inode and fix their
  69                  * d_flags to indicate parental interest (their parent is the
  70                  * original inode) */
  71                 spin_lock(&alias->d_lock);
  72                 list_for_each_entry(child, &alias->d_subdirs, d_child) {
  73                         if (!child->d_inode)
  74                                 continue;
  75
  76                         spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
  77                         if (watched)
  78                                 child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
  79                         else
  80                                 child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
  81                         spin_unlock(&child->d_lock);
  82                 }
  83                 spin_unlock(&alias->d_lock);
  84         }
  85         spin_unlock(&inode->i_lock);
  86 }
  87
  88 /* Notify this dentry's parent about a child's events. */
  89 int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask)
  90 {
  91         struct dentry *parent;
  92         struct inode *p_inode;
  93         int ret = 0;
  94
  95         if (!dentry)
  96                 dentry = path->dentry;
  97
  98         if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
  99                 return 0;
 100
 101         parent = dget_parent(dentry);
 102         p_inode = parent->d_inode;
 103
 104         if (unlikely(!fsnotify_inode_watches_children(p_inode)))
 105                 __fsnotify_update_child_dentry_flags(p_inode);
 106         else if (p_inode->i_fsnotify_mask & mask) {
 107                 /* we are notifying a parent so come up with the new mask which
 108                  * specifies these are events which came from a child. */
 109                 mask |= FS_EVENT_ON_CHILD;
 110
 111                 if (path)
 112                         ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
 113                                        dentry->d_name.name, 0);
 114                 else
 115                         ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
 116                                        dentry->d_name.name, 0);
 117         }
 118
 119         dput(parent);
 120
 121         return ret;
 122 }
 123 EXPORT_SYMBOL_GPL(__fsnotify_parent);
 124
 125 static int send_to_group(struct inode *to_tell,
 126                          struct fsnotify_mark *inode_mark,
 127                          struct fsnotify_mark *vfsmount_mark,
 128                          __u32 mask, void *data,
 129                          int data_is, u32 cookie,
 130                          const unsigned char *file_name)
 131 {
 132         struct fsnotify_group *group = NULL;
 133         __u32 inode_test_mask = 0;
 134         __u32 vfsmount_test_mask = 0;
 135
 136         if (unlikely(!inode_mark && !vfsmount_mark)) {
 137                 BUG();
 138                 return 0;
 139         }
 140
 141         /* clear ignored on inode modification */
 142         if (mask & FS_MODIFY) {
 143                 if (inode_mark &&
 144                     !(inode_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
 145                         inode_mark->ignored_mask = 0;
 146                 if (vfsmount_mark &&
 147                     !(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
 148                         vfsmount_mark->ignored_mask = 0;
 149         }
 150
 151         /* does the inode mark tell us to do something? */
 152         if (inode_mark) {
 153                 group = inode_mark->group;
 154                 inode_test_mask = (mask & ~FS_EVENT_ON_CHILD);
 155                 inode_test_mask &= inode_mark->mask;
 156                 inode_test_mask &= ~inode_mark->ignored_mask;
 157         }
 158
 159         /* does the vfsmount_mark tell us to do something? */
 160         if (vfsmount_mark) {
 161                 vfsmount_test_mask = (mask & ~FS_EVENT_ON_CHILD);
 162                 group = vfsmount_mark->group;
 163                 vfsmount_test_mask &= vfsmount_mark->mask;
 164                 vfsmount_test_mask &= ~vfsmount_mark->ignored_mask;
 165                 if (inode_mark)
 166                         vfsmount_test_mask &= ~inode_mark->ignored_mask;
 167         }
 168
 169         pr_debug("%s: group=%p to_tell=%p mask=%x inode_mark=%p"
 170                  " inode_test_mask=%x vfsmount_mark=%p vfsmount_test_mask=%x"
 171                  " data=%p data_is=%d cookie=%d\n",
 172                  __func__, group, to_tell, mask, inode_mark,
 173                  inode_test_mask, vfsmount_mark, vfsmount_test_mask, data,
 174                  data_is, cookie);
 175
 176         if (!inode_test_mask && !vfsmount_test_mask)
 177                 return 0;
 178
 179         return group->ops->handle_event(group, to_tell, inode_mark,
 180                                         vfsmount_mark, mask, data, data_is,
 181                                         file_name, cookie);
 182 }
 183
 184 /*
 185  * This is the main call to fsnotify.  The VFS calls into hook specific functions
 186  * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
 187  * out to all of the registered fsnotify_group.  Those groups can then use the
 188  * notification event in whatever means they feel necessary.
 189  */
 190 int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
 191              const unsigned char *file_name, u32 cookie)
 192 {
 193         struct hlist_node *inode_node = NULL, *vfsmount_node = NULL;
 194         struct fsnotify_mark *inode_mark = NULL, *vfsmount_mark = NULL;
 195         struct fsnotify_group *inode_group, *vfsmount_group;
 196         struct mount *mnt;
 197         int idx, ret = 0;
 198         /* global tests shouldn't care about events on child only the specific event */
 199         __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
 200
 201         if (data_is == FSNOTIFY_EVENT_PATH)
 202                 mnt = real_mount(((struct path *)data)->mnt);
 203         else
 204                 mnt = NULL;
 205
 206         /*
 207          * Optimization: srcu_read_lock() has a memory barrier which can
 208          * be expensive.  It protects walking the *_fsnotify_marks lists.
 209          * However, if we do not walk the lists, we do not have to do
 210          * SRCU because we have no references to any objects and do not
 211          * need SRCU to keep them "alive".
 212          */
 213         if (hlist_empty(&to_tell->i_fsnotify_marks) &&
 214             (!mnt || hlist_empty(&mnt->mnt_fsnotify_marks)))
 215                 return 0;
 216         /*
 217          * if this is a modify event we may need to clear the ignored masks
 218          * otherwise return if neither the inode nor the vfsmount care about
 219          * this type of event.
 220          */
 221         if (!(mask & FS_MODIFY) &&
 222             !(test_mask & to_tell->i_fsnotify_mask) &&
 223             !(mnt && test_mask & mnt->mnt_fsnotify_mask))
 224                 return 0;
 225
 226         idx = srcu_read_lock(&fsnotify_mark_srcu);
 227
 228         if ((mask & FS_MODIFY) ||
 229             (test_mask & to_tell->i_fsnotify_mask))
 230                 inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
 231                                               &fsnotify_mark_srcu);
 232
 233         if (mnt && ((mask & FS_MODIFY) ||
 234                     (test_mask & mnt->mnt_fsnotify_mask))) {
 235                 vfsmount_node = srcu_dereference(mnt->mnt_fsnotify_marks.first,
 236                                                  &fsnotify_mark_srcu);
 237                 inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
 238                                               &fsnotify_mark_srcu);
 239         }
 240
 241         /*
 242          * We need to merge inode & vfsmount mark lists so that inode mark
 243          * ignore masks are properly reflected for mount mark notifications.
 244          * That's why this traversal is so complicated...
 245          */
 246         while (inode_node || vfsmount_node) {
 247                 inode_group = NULL;
 248                 inode_mark = NULL;
 249                 vfsmount_group = NULL;
 250                 vfsmount_mark = NULL;
 251
 252                 if (inode_node) {
 253                         inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
 254                                                  struct fsnotify_mark, obj_list);
 255                         inode_group = inode_mark->group;
 256                 }
 257
 258                 if (vfsmount_node) {
 259                         vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
 260                                                     struct fsnotify_mark, obj_list);
 261                         vfsmount_group = vfsmount_mark->group;
 262                 }
 263
 264                 if (inode_group && vfsmount_group) {
 265                         int cmp = fsnotify_compare_groups(inode_group,
 266                                                           vfsmount_group);
 267                         if (cmp > 0) {
 268                                 inode_group = NULL;
 269                                 inode_mark = NULL;
 270                         } else if (cmp < 0) {
 271                                 vfsmount_group = NULL;
 272                                 vfsmount_mark = NULL;
 273                         }
 274                 }
 275                 ret = send_to_group(to_tell, inode_mark, vfsmount_mark, mask,
 276                                     data, data_is, cookie, file_name);
 277
 278                 if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
 279                         goto out;
 280
 281                 if (inode_group)
 282                         inode_node = srcu_dereference(inode_node->next,
 283                                                       &fsnotify_mark_srcu);
 284                 if (vfsmount_group)
 285                         vfsmount_node = srcu_dereference(vfsmount_node->next,
 286                                                          &fsnotify_mark_srcu);
 287         }
 288         ret = 0;
 289 out:
 290         srcu_read_unlock(&fsnotify_mark_srcu, idx);
 291
 292         return ret;
 293 }
 294 EXPORT_SYMBOL_GPL(fsnotify);
 295
 296 static __init int fsnotify_init(void)
 297 {
 298         int ret;
 299
 300         BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
 301
 302         ret = init_srcu_struct(&fsnotify_mark_srcu);
 303         if (ret)
 304                 panic("initializing fsnotify_mark_srcu");
 305
 306         return 0;
 307 }
 308 core_initcall(fsnotify_init);