include/linux/fsnotify_backend.h

   1 /*
   2  * Filesystem access notification for Linux
   3  *
   4  *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
   5  */
   6
   7 #ifndef __LINUX_FSNOTIFY_BACKEND_H
   8 #define __LINUX_FSNOTIFY_BACKEND_H
   9
  10 #ifdef __KERNEL__
  11
  12 #include <linux/idr.h> /* inotify uses this */
  13 #include <linux/fs.h> /* struct inode */
  14 #include <linux/list.h>
  15 #include <linux/path.h> /* struct path */
  16 #include <linux/spinlock.h>
  17 #include <linux/types.h>
  18
  19 #include <asm/atomic.h>
  20
  21 /*
  22  * IN_* from inotfy.h lines up EXACTLY with FS_*, this is so we can easily
  23  * convert between them.  dnotify only needs conversion at watch creation
  24  * so no perf loss there.  fanotify isn't defined yet, so it can use the
  25  * wholes if it needs more events.
  26  */
  27 #define FS_ACCESS               0x00000001      /* File was accessed */
  28 #define FS_MODIFY               0x00000002      /* File was modified */
  29 #define FS_ATTRIB               0x00000004      /* Metadata changed */
  30 #define FS_CLOSE_WRITE          0x00000008      /* Writtable file was closed */
  31 #define FS_CLOSE_NOWRITE        0x00000010      /* Unwrittable file closed */
  32 #define FS_OPEN                 0x00000020      /* File was opened */
  33 #define FS_MOVED_FROM           0x00000040      /* File was moved from X */
  34 #define FS_MOVED_TO             0x00000080      /* File was moved to Y */
  35 #define FS_CREATE               0x00000100      /* Subfile was created */
  36 #define FS_DELETE               0x00000200      /* Subfile was deleted */
  37 #define FS_DELETE_SELF          0x00000400      /* Self was deleted */
  38 #define FS_MOVE_SELF            0x00000800      /* Self was moved */
  39
  40 #define FS_UNMOUNT              0x00002000      /* inode on umount fs */
  41 #define FS_Q_OVERFLOW           0x00004000      /* Event queued overflowed */
  42 #define FS_IN_IGNORED           0x00008000      /* last inotify event here */
  43
  44 #define FS_IN_ISDIR             0x40000000      /* event occurred against dir */
  45 #define FS_IN_ONESHOT           0x80000000      /* only send event once */
  46
  47 #define FS_DN_RENAME            0x10000000      /* file renamed */
  48 #define FS_DN_MULTISHOT         0x20000000      /* dnotify multishot */
  49
  50 /* This inode cares about things that happen to its children.  Always set for
  51  * dnotify and inotify. */
  52 #define FS_EVENT_ON_CHILD       0x08000000
  53
  54 /* This is a list of all events that may get sent to a parernt based on fs event
  55  * happening to inodes inside that directory */
  56 #define FS_EVENTS_POSS_ON_CHILD   (FS_ACCESS | FS_MODIFY | FS_ATTRIB |\
  57                                    FS_CLOSE_WRITE | FS_CLOSE_NOWRITE | FS_OPEN |\
  58                                    FS_MOVED_FROM | FS_MOVED_TO | FS_CREATE |\
  59                                    FS_DELETE)
  60
  61 /* listeners that hard code group numbers near the top */
  62 #define DNOTIFY_GROUP_NUM       UINT_MAX
  63 #define INOTIFY_GROUP_NUM       (DNOTIFY_GROUP_NUM-1)
  64
  65 struct fsnotify_group;
  66 struct fsnotify_event;
  67 struct fsnotify_mark_entry;
  68 struct fsnotify_event_private_data;
  69
  70 /*
  71  * Each group much define these ops.  The fsnotify infrastructure will call
  72  * these operations for each relevant group.
  73  *
  74  * should_send_event - given a group, inode, and mask this function determines
  75  *              if the group is interested in this event.
  76  * handle_event - main call for a group to handle an fs event
  77  * free_group_priv - called when a group refcnt hits 0 to clean up the private union
  78  * freeing-mark - this means that a mark has been flagged to die when everything
  79  *              finishes using it.  The function is supplied with what must be a
  80  *              valid group and inode to use to clean up.
  81  */
  82 struct fsnotify_ops {
  83         bool (*should_send_event)(struct fsnotify_group *group, struct inode *inode, __u32 mask);
  84         int (*handle_event)(struct fsnotify_group *group, struct fsnotify_event *event);
  85         void (*free_group_priv)(struct fsnotify_group *group);
  86         void (*freeing_mark)(struct fsnotify_mark_entry *entry, struct fsnotify_group *group);
  87         void (*free_event_priv)(struct fsnotify_event_private_data *priv);
  88 };
  89
  90 /*
  91  * A group is a "thing" that wants to receive notification about filesystem
  92  * events.  The mask holds the subset of event types this group cares about.
  93  * refcnt on a group is up to the implementor and at any moment if it goes 0
  94  * everything will be cleaned up.
  95  */
  96 struct fsnotify_group {
  97         /*
  98          * global list of all groups receiving events from fsnotify.
  99          * anchored by fsnotify_groups and protected by either fsnotify_grp_mutex
 100          * or fsnotify_grp_srcu depending on write vs read.
 101          */
 102         struct list_head group_list;
 103
 104         /*
 105          * Defines all of the event types in which this group is interested.
 106          * This mask is a bitwise OR of the FS_* events from above.  Each time
 107          * this mask changes for a group (if it changes) the correct functions
 108          * must be called to update the global structures which indicate global
 109          * interest in event types.
 110          */
 111         __u32 mask;
 112
 113         /*
 114          * How the refcnt is used is up to each group.  When the refcnt hits 0
 115          * fsnotify will clean up all of the resources associated with this group.
 116          * As an example, the dnotify group will always have a refcnt=1 and that
 117          * will never change.  Inotify, on the other hand, has a group per
 118          * inotify_init() and the refcnt will hit 0 only when that fd has been
 119          * closed.
 120          */
 121         atomic_t refcnt;                /* things with interest in this group */
 122         unsigned int group_num;         /* simply prevents accidental group collision */
 123
 124         const struct fsnotify_ops *ops; /* how this group handles things */
 125
 126         /* needed to send notification to userspace */
 127         struct mutex notification_mutex;        /* protect the notification_list */
 128         struct list_head notification_list;     /* list of event_holder this group needs to send to userspace */
 129         wait_queue_head_t notification_waitq;   /* read() on the notification file blocks on this waitq */
 130         unsigned int q_len;                     /* events on the queue */
 131         unsigned int max_events;                /* maximum events allowed on the list */
 132
 133         /* stores all fastapth entries assoc with this group so they can be cleaned on unregister */
 134         spinlock_t mark_lock;           /* protect mark_entries list */
 135         atomic_t num_marks;             /* 1 for each mark entry and 1 for not being
 136                                          * past the point of no return when freeing
 137                                          * a group */
 138         struct list_head mark_entries;  /* all inode mark entries for this group */
 139
 140         /* prevents double list_del of group_list.  protected by global fsnotify_grp_mutex */
 141         bool on_group_list;
 142
 143         /* groups can define private fields here or use the void *private */
 144         union {
 145                 void *private;
 146 #ifdef CONFIG_INOTIFY_USER
 147                 struct inotify_group_private_data {
 148                         spinlock_t      idr_lock;
 149                         struct idr      idr;
 150                         u32             last_wd;
 151                         struct fasync_struct    *fa;    /* async notification */
 152                         struct user_struct      *user;
 153                 } inotify_data;
 154 #endif
 155         };
 156 };
 157
 158 /*
 159  * A single event can be queued in multiple group->notification_lists.
 160  *
 161  * each group->notification_list will point to an event_holder which in turns points
 162  * to the actual event that needs to be sent to userspace.
 163  *
 164  * Seemed cheaper to create a refcnt'd event and a small holder for every group
 165  * than create a different event for every group
 166  *
 167  */
 168 struct fsnotify_event_holder {
 169         struct fsnotify_event *event;
 170         struct list_head event_list;
 171 };
 172
 173 /*
 174  * Inotify needs to tack data onto an event.  This struct lets us later find the
 175  * correct private data of the correct group.
 176  */
 177 struct fsnotify_event_private_data {
 178         struct fsnotify_group *group;
 179         struct list_head event_list;
 180 };
 181
 182 /*
 183  * all of the information about the original object we want to now send to
 184  * a group.  If you want to carry more info from the accessing task to the
 185  * listener this structure is where you need to be adding fields.
 186  */
 187 struct fsnotify_event {
 188         /*
 189          * If we create an event we are also likely going to need a holder
 190          * to link to a group.  So embed one holder in the event.  Means only
 191          * one allocation for the common case where we only have one group
 192          */
 193         struct fsnotify_event_holder holder;
 194         spinlock_t lock;        /* protection for the associated event_holder and private_list */
 195         /* to_tell may ONLY be dereferenced during handle_event(). */
 196         struct inode *to_tell;  /* either the inode the event happened to or its parent */
 197         /*
 198          * depending on the event type we should have either a path or inode
 199          * We hold a reference on path, but NOT on inode.  Since we have the ref on
 200          * the path, it may be dereferenced at any point during this object's
 201          * lifetime.  That reference is dropped when this object's refcnt hits
 202          * 0.  If this event contains an inode instead of a path, the inode may
 203          * ONLY be used during handle_event().
 204          */
 205         union {
 206                 struct path path;
 207                 struct inode *inode;
 208         };
 209 /* when calling fsnotify tell it if the data is a path or inode */
 210 #define FSNOTIFY_EVENT_NONE     0
 211 #define FSNOTIFY_EVENT_PATH     1
 212 #define FSNOTIFY_EVENT_INODE    2
 213 #define FSNOTIFY_EVENT_FILE     3
 214         int data_type;          /* which of the above union we have */
 215         atomic_t refcnt;        /* how many groups still are using/need to send this event */
 216         __u32 mask;             /* the type of access, bitwise OR for FS_* event types */
 217
 218         u32 sync_cookie;        /* used to corrolate events, namely inotify mv events */
 219         char *file_name;
 220         size_t name_len;
 221
 222         struct list_head private_data_list;     /* groups can store private data here */
 223 };
 224
 225 /*
 226  * a mark is simply an entry attached to an in core inode which allows an
 227  * fsnotify listener to indicate they are either no longer interested in events
 228  * of a type matching mask or only interested in those events.
 229  *
 230  * these are flushed when an inode is evicted from core and may be flushed
 231  * when the inode is modified (as seen by fsnotify_access).  Some fsnotify users
 232  * (such as dnotify) will flush these when the open fd is closed and not at
 233  * inode eviction or modification.
 234  */
 235 struct fsnotify_mark_entry {
 236         __u32 mask;                     /* mask this mark entry is for */
 237         /* we hold ref for each i_list and g_list.  also one ref for each 'thing'
 238          * in kernel that found and may be using this mark. */
 239         atomic_t refcnt;                /* active things looking at this mark */
 240         struct inode *inode;            /* inode this entry is associated with */
 241         struct fsnotify_group *group;   /* group this mark entry is for */
 242         struct hlist_node i_list;       /* list of mark_entries by inode->i_fsnotify_mark_entries */
 243         struct list_head g_list;        /* list of mark_entries by group->i_fsnotify_mark_entries */
 244         spinlock_t lock;                /* protect group, inode, and killme */
 245         struct list_head free_i_list;   /* tmp list used when freeing this mark */
 246         struct list_head free_g_list;   /* tmp list used when freeing this mark */
 247         void (*free_mark)(struct fsnotify_mark_entry *entry); /* called on final put+free */
 248 };
 249
 250 #ifdef CONFIG_FSNOTIFY
 251
 252 /* called from the vfs helpers */
 253
 254 /* main fsnotify call to send events */
 255 extern void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
 256                      const char *name, u32 cookie);
 257 extern void __fsnotify_parent(struct dentry *dentry, __u32 mask);
 258 extern void __fsnotify_inode_delete(struct inode *inode);
 259 extern u32 fsnotify_get_cookie(void);
 260
 261 static inline int fsnotify_inode_watches_children(struct inode *inode)
 262 {
 263         /* FS_EVENT_ON_CHILD is set if the inode may care */
 264         if (!(inode->i_fsnotify_mask & FS_EVENT_ON_CHILD))
 265                 return 0;
 266         /* this inode might care about child events, does it care about the
 267          * specific set of events that can happen on a child? */
 268         return inode->i_fsnotify_mask & FS_EVENTS_POSS_ON_CHILD;
 269 }
 270
 271 /*
 272  * Update the dentry with a flag indicating the interest of its parent to receive
 273  * filesystem events when those events happens to this dentry->d_inode.
 274  */
 275 static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
 276 {
 277         struct dentry *parent;
 278
 279         assert_spin_locked(&dcache_lock);
 280         assert_spin_locked(&dentry->d_lock);
 281
 282         parent = dentry->d_parent;
 283         if (parent->d_inode && fsnotify_inode_watches_children(parent->d_inode))
 284                 dentry->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
 285         else
 286                 dentry->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
 287 }
 288
 289 /*
 290  * fsnotify_d_instantiate - instantiate a dentry for inode
 291  * Called with dcache_lock held.
 292  */
 293 static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
 294 {
 295         if (!inode)
 296                 return;
 297
 298         assert_spin_locked(&dcache_lock);
 299
 300         spin_lock(&dentry->d_lock);
 301         __fsnotify_update_dcache_flags(dentry);
 302         spin_unlock(&dentry->d_lock);
 303 }
 304
 305 /* called from fsnotify listeners, such as fanotify or dnotify */
 306
 307 /* must call when a group changes its ->mask */
 308 extern void fsnotify_recalc_global_mask(void);
 309 /* get a reference to an existing or create a new group */
 310 extern struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num,
 311                                                     __u32 mask,
 312                                                     const struct fsnotify_ops *ops);
 313 /* run all marks associated with this group and update group->mask */
 314 extern void fsnotify_recalc_group_mask(struct fsnotify_group *group);
 315 /* drop reference on a group from fsnotify_obtain_group */
 316 extern void fsnotify_put_group(struct fsnotify_group *group);
 317
 318 /* take a reference to an event */
 319 extern void fsnotify_get_event(struct fsnotify_event *event);
 320 extern void fsnotify_put_event(struct fsnotify_event *event);
 321 /* find private data previously attached to an event and unlink it */
 322 extern struct fsnotify_event_private_data *fsnotify_remove_priv_from_event(struct fsnotify_group *group,
 323                                                                            struct fsnotify_event *event);
 324
 325 /* attach the event to the group notification queue */
 326 extern int fsnotify_add_notify_event(struct fsnotify_group *group, struct fsnotify_event *event,
 327                                      struct fsnotify_event_private_data *priv);
 328 /* true if the group notification queue is empty */
 329 extern bool fsnotify_notify_queue_is_empty(struct fsnotify_group *group);
 330 /* return, but do not dequeue the first event on the notification queue */
 331 extern struct fsnotify_event *fsnotify_peek_notify_event(struct fsnotify_group *group);
 332 /* return AND dequeue the first event on the notification queue */
 333 extern struct fsnotify_event *fsnotify_remove_notify_event(struct fsnotify_group *group);
 334
 335 /* functions used to manipulate the marks attached to inodes */
 336
 337 /* run all marks associated with an inode and update inode->i_fsnotify_mask */
 338 extern void fsnotify_recalc_inode_mask(struct inode *inode);
 339 extern void fsnotify_init_mark(struct fsnotify_mark_entry *entry, void (*free_mark)(struct fsnotify_mark_entry *entry));
 340 /* find (and take a reference) to a mark associated with group and inode */
 341 extern struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group, struct inode *inode);
 342 /* attach the mark to both the group and the inode */
 343 extern int fsnotify_add_mark(struct fsnotify_mark_entry *entry, struct fsnotify_group *group, struct inode *inode);
 344 /* given a mark, flag it to be freed when all references are dropped */
 345 extern void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry);
 346 /* run all the marks in a group, and flag them to be freed */
 347 extern void fsnotify_clear_marks_by_group(struct fsnotify_group *group);
 348 extern void fsnotify_get_mark(struct fsnotify_mark_entry *entry);
 349 extern void fsnotify_put_mark(struct fsnotify_mark_entry *entry);
 350 extern void fsnotify_unmount_inodes(struct list_head *list);
 351
 352 /* put here because inotify does some weird stuff when destroying watches */
 353 extern struct fsnotify_event *fsnotify_create_event(struct inode *to_tell, __u32 mask,
 354                                                     void *data, int data_is, const char *name,
 355                                                     u32 cookie, gfp_t gfp);
 356
 357 #else
 358
 359 static inline void fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
 360                             const char *name, u32 cookie)
 361 {}
 362
 363 static inline void __fsnotify_parent(struct dentry *dentry, __u32 mask)
 364 {}
 365
 366 static inline void __fsnotify_inode_delete(struct inode *inode)
 367 {}
 368
 369 static inline void __fsnotify_update_dcache_flags(struct dentry *dentry)
 370 {}
 371
 372 static inline void __fsnotify_d_instantiate(struct dentry *dentry, struct inode *inode)
 373 {}
 374
 375 static inline u32 fsnotify_get_cookie(void)
 376 {
 377         return 0;
 378 }
 379
 380 static inline void fsnotify_unmount_inodes(struct list_head *list)
 381 {}
 382
 383 #endif  /* CONFIG_FSNOTIFY */
 384
 385 #endif  /* __KERNEL __ */
 386
 387 #endif  /* __LINUX_FSNOTIFY_BACKEND_H */