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(const 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                 struct name_snapshot name;
 108
 109                 /* we are notifying a parent so come up with the new mask which
 110                  * specifies these are events which came from a child. */
 111                 mask |= FS_EVENT_ON_CHILD;
 112
 113                 take_dentry_name_snapshot(&name, dentry);
 114                 if (path)
 115                         ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
 116                                        name.name, 0);
 117                 else
 118                         ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
 119                                        name.name, 0);
 120                 release_dentry_name_snapshot(&name);
 121         }
 122
 123         dput(parent);
 124
 125         return ret;
 126 }
 127 EXPORT_SYMBOL_GPL(__fsnotify_parent);
 128
 129 static int send_to_group(struct inode *to_tell,
 130                          struct fsnotify_mark *inode_mark,
 131                          struct fsnotify_mark *vfsmount_mark,
 132                          __u32 mask, const void *data,
 133                          int data_is, u32 cookie,
 134                          const unsigned char *file_name)
 135 {
 136         struct fsnotify_group *group = NULL;
 137         __u32 inode_test_mask = 0;
 138         __u32 vfsmount_test_mask = 0;
 139
 140         if (unlikely(!inode_mark && !vfsmount_mark)) {
 141                 BUG();
 142                 return 0;
 143         }
 144
 145         /* clear ignored on inode modification */
 146         if (mask & FS_MODIFY) {
 147                 if (inode_mark &&
 148                     !(inode_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
 149                         inode_mark->ignored_mask = 0;
 150                 if (vfsmount_mark &&
 151                     !(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
 152                         vfsmount_mark->ignored_mask = 0;
 153         }
 154
 155         /* does the inode mark tell us to do something? */
 156         if (inode_mark) {
 157                 group = inode_mark->group;
 158                 inode_test_mask = (mask & ~FS_EVENT_ON_CHILD);
 159                 inode_test_mask &= inode_mark->mask;
 160                 inode_test_mask &= ~inode_mark->ignored_mask;
 161         }
 162
 163         /* does the vfsmount_mark tell us to do something? */
 164         if (vfsmount_mark) {
 165                 vfsmount_test_mask = (mask & ~FS_EVENT_ON_CHILD);
 166                 group = vfsmount_mark->group;
 167                 vfsmount_test_mask &= vfsmount_mark->mask;
 168                 vfsmount_test_mask &= ~vfsmount_mark->ignored_mask;
 169                 if (inode_mark)
 170                         vfsmount_test_mask &= ~inode_mark->ignored_mask;
 171         }
 172
 173         pr_debug("%s: group=%p to_tell=%p mask=%x inode_mark=%p"
 174                  " inode_test_mask=%x vfsmount_mark=%p vfsmount_test_mask=%x"
 175                  " data=%p data_is=%d cookie=%d\n",
 176                  __func__, group, to_tell, mask, inode_mark,
 177                  inode_test_mask, vfsmount_mark, vfsmount_test_mask, data,
 178                  data_is, cookie);
 179
 180         if (!inode_test_mask && !vfsmount_test_mask)
 181                 return 0;
 182
 183         return group->ops->handle_event(group, to_tell, inode_mark,
 184                                         vfsmount_mark, mask, data, data_is,
 185                                         file_name, cookie);
 186 }
 187
 188 /*
 189  * This is the main call to fsnotify.  The VFS calls into hook specific functions
 190  * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
 191  * out to all of the registered fsnotify_group.  Those groups can then use the
 192  * notification event in whatever means they feel necessary.
 193  */
 194 int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
 195              const unsigned char *file_name, u32 cookie)
 196 {
 197         struct hlist_node *inode_node = NULL, *vfsmount_node = NULL;
 198         struct fsnotify_mark *inode_mark = NULL, *vfsmount_mark = NULL;
 199         struct fsnotify_group *inode_group, *vfsmount_group;
 200         struct mount *mnt;
 201         int idx, ret = 0;
 202         /* global tests shouldn't care about events on child only the specific event */
 203         __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
 204
 205         if (data_is == FSNOTIFY_EVENT_PATH)
 206                 mnt = real_mount(((const struct path *)data)->mnt);
 207         else
 208                 mnt = NULL;
 209
 210         /*
 211          * Optimization: srcu_read_lock() has a memory barrier which can
 212          * be expensive.  It protects walking the *_fsnotify_marks lists.
 213          * However, if we do not walk the lists, we do not have to do
 214          * SRCU because we have no references to any objects and do not
 215          * need SRCU to keep them "alive".
 216          */
 217         if (hlist_empty(&to_tell->i_fsnotify_marks) &&
 218             (!mnt || hlist_empty(&mnt->mnt_fsnotify_marks)))
 219                 return 0;
 220         /*
 221          * if this is a modify event we may need to clear the ignored masks
 222          * otherwise return if neither the inode nor the vfsmount care about
 223          * this type of event.
 224          */
 225         if (!(mask & FS_MODIFY) &&
 226             !(test_mask & to_tell->i_fsnotify_mask) &&
 227             !(mnt && test_mask & mnt->mnt_fsnotify_mask))
 228                 return 0;
 229
 230         idx = srcu_read_lock(&fsnotify_mark_srcu);
 231
 232         if ((mask & FS_MODIFY) ||
 233             (test_mask & to_tell->i_fsnotify_mask))
 234                 inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
 235                                               &fsnotify_mark_srcu);
 236
 237         if (mnt && ((mask & FS_MODIFY) ||
 238                     (test_mask & mnt->mnt_fsnotify_mask))) {
 239                 vfsmount_node = srcu_dereference(mnt->mnt_fsnotify_marks.first,
 240                                                  &fsnotify_mark_srcu);
 241                 inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
 242                                               &fsnotify_mark_srcu);
 243         }
 244
 245         /*
 246          * We need to merge inode & vfsmount mark lists so that inode mark
 247          * ignore masks are properly reflected for mount mark notifications.
 248          * That's why this traversal is so complicated...
 249          */
 250         while (inode_node || vfsmount_node) {
 251                 inode_group = NULL;
 252                 inode_mark = NULL;
 253                 vfsmount_group = NULL;
 254                 vfsmount_mark = NULL;
 255
 256                 if (inode_node) {
 257                         inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
 258                                                  struct fsnotify_mark, obj_list);
 259                         inode_group = inode_mark->group;
 260                 }
 261
 262                 if (vfsmount_node) {
 263                         vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
 264                                                     struct fsnotify_mark, obj_list);
 265                         vfsmount_group = vfsmount_mark->group;
 266                 }
 267
 268                 if (inode_group && vfsmount_group) {
 269                         int cmp = fsnotify_compare_groups(inode_group,
 270                                                           vfsmount_group);
 271                         if (cmp > 0) {
 272                                 inode_group = NULL;
 273                                 inode_mark = NULL;
 274                         } else if (cmp < 0) {
 275                                 vfsmount_group = NULL;
 276                                 vfsmount_mark = NULL;
 277                         }
 278                 }
 279                 ret = send_to_group(to_tell, inode_mark, vfsmount_mark, mask,
 280                                     data, data_is, cookie, file_name);
 281
 282                 if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
 283                         goto out;
 284
 285                 if (inode_group)
 286                         inode_node = srcu_dereference(inode_node->next,
 287                                                       &fsnotify_mark_srcu);
 288                 if (vfsmount_group)
 289                         vfsmount_node = srcu_dereference(vfsmount_node->next,
 290                                                          &fsnotify_mark_srcu);
 291         }
 292         ret = 0;
 293 out:
 294         srcu_read_unlock(&fsnotify_mark_srcu, idx);
 295
 296         return ret;
 297 }
 298 EXPORT_SYMBOL_GPL(fsnotify);
 299
 300 static __init int fsnotify_init(void)
 301 {
 302         int ret;
 303
 304         BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
 305
 306         ret = init_srcu_struct(&fsnotify_mark_srcu);
 307         if (ret)
 308                 panic("initializing fsnotify_mark_srcu");
 309
 310         return 0;
 311 }
 312 core_initcall(fsnotify_init);