linux/fs/notify/dnotify/dnotify.c
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   1/*
   2 * Directory notifications for Linux.
   3 *
   4 * Copyright (C) 2000,2001,2002 Stephen Rothwell
   5 *
   6 * Copyright (C) 2009 Eric Paris <Red Hat Inc>
   7 * dnotify was largly rewritten to use the new fsnotify infrastructure
   8 *
   9 * This program is free software; you can redistribute it and/or modify it
  10 * under the terms of the GNU General Public License as published by the
  11 * Free Software Foundation; either version 2, or (at your option) any
  12 * later version.
  13 *
  14 * This program is distributed in the hope that it will be useful, but
  15 * WITHOUT ANY WARRANTY; without even the implied warranty of
  16 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  17 * General Public License for more details.
  18 */
  19#include <linux/fs.h>
  20#include <linux/module.h>
  21#include <linux/sched.h>
  22#include <linux/dnotify.h>
  23#include <linux/init.h>
  24#include <linux/spinlock.h>
  25#include <linux/slab.h>
  26#include <linux/fdtable.h>
  27#include <linux/fsnotify_backend.h>
  28
  29int dir_notify_enable __read_mostly = 1;
  30
  31static struct kmem_cache *dnotify_struct_cache __read_mostly;
  32static struct kmem_cache *dnotify_mark_cache __read_mostly;
  33static struct fsnotify_group *dnotify_group __read_mostly;
  34
  35/*
  36 * dnotify will attach one of these to each inode (i_fsnotify_marks) which
  37 * is being watched by dnotify.  If multiple userspace applications are watching
  38 * the same directory with dnotify their information is chained in dn
  39 */
  40struct dnotify_mark {
  41        struct fsnotify_mark fsn_mark;
  42        struct dnotify_struct *dn;
  43};
  44
  45/*
  46 * When a process starts or stops watching an inode the set of events which
  47 * dnotify cares about for that inode may change.  This function runs the
  48 * list of everything receiving dnotify events about this directory and calculates
  49 * the set of all those events.  After it updates what dnotify is interested in
  50 * it calls the fsnotify function so it can update the set of all events relevant
  51 * to this inode.
  52 */
  53static void dnotify_recalc_inode_mask(struct fsnotify_mark *fsn_mark)
  54{
  55        __u32 new_mask = 0;
  56        struct dnotify_struct *dn;
  57        struct dnotify_mark *dn_mark  = container_of(fsn_mark,
  58                                                     struct dnotify_mark,
  59                                                     fsn_mark);
  60
  61        assert_spin_locked(&fsn_mark->lock);
  62
  63        for (dn = dn_mark->dn; dn != NULL; dn = dn->dn_next)
  64                new_mask |= (dn->dn_mask & ~FS_DN_MULTISHOT);
  65        if (fsn_mark->mask == new_mask)
  66                return;
  67        fsn_mark->mask = new_mask;
  68
  69        fsnotify_recalc_mask(fsn_mark->connector);
  70}
  71
  72/*
  73 * Mains fsnotify call where events are delivered to dnotify.
  74 * Find the dnotify mark on the relevant inode, run the list of dnotify structs
  75 * on that mark and determine which of them has expressed interest in receiving
  76 * events of this type.  When found send the correct process and signal and
  77 * destroy the dnotify struct if it was not registered to receive multiple
  78 * events.
  79 */
  80static int dnotify_handle_event(struct fsnotify_group *group,
  81                                struct inode *inode,
  82                                struct fsnotify_mark *inode_mark,
  83                                struct fsnotify_mark *vfsmount_mark,
  84                                u32 mask, const void *data, int data_type,
  85                                const unsigned char *file_name, u32 cookie,
  86                                struct fsnotify_iter_info *iter_info)
  87{
  88        struct dnotify_mark *dn_mark;
  89        struct dnotify_struct *dn;
  90        struct dnotify_struct **prev;
  91        struct fown_struct *fown;
  92        __u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
  93
  94        /* not a dir, dnotify doesn't care */
  95        if (!S_ISDIR(inode->i_mode))
  96                return 0;
  97
  98        BUG_ON(vfsmount_mark);
  99
 100        dn_mark = container_of(inode_mark, struct dnotify_mark, fsn_mark);
 101
 102        spin_lock(&inode_mark->lock);
 103        prev = &dn_mark->dn;
 104        while ((dn = *prev) != NULL) {
 105                if ((dn->dn_mask & test_mask) == 0) {
 106                        prev = &dn->dn_next;
 107                        continue;
 108                }
 109                fown = &dn->dn_filp->f_owner;
 110                send_sigio(fown, dn->dn_fd, POLL_MSG);
 111                if (dn->dn_mask & FS_DN_MULTISHOT)
 112                        prev = &dn->dn_next;
 113                else {
 114                        *prev = dn->dn_next;
 115                        kmem_cache_free(dnotify_struct_cache, dn);
 116                        dnotify_recalc_inode_mask(inode_mark);
 117                }
 118        }
 119
 120        spin_unlock(&inode_mark->lock);
 121
 122        return 0;
 123}
 124
 125static void dnotify_free_mark(struct fsnotify_mark *fsn_mark)
 126{
 127        struct dnotify_mark *dn_mark = container_of(fsn_mark,
 128                                                    struct dnotify_mark,
 129                                                    fsn_mark);
 130
 131        BUG_ON(dn_mark->dn);
 132
 133        kmem_cache_free(dnotify_mark_cache, dn_mark);
 134}
 135
 136static const struct fsnotify_ops dnotify_fsnotify_ops = {
 137        .handle_event = dnotify_handle_event,
 138        .free_mark = dnotify_free_mark,
 139};
 140
 141/*
 142 * Called every time a file is closed.  Looks first for a dnotify mark on the
 143 * inode.  If one is found run all of the ->dn structures attached to that
 144 * mark for one relevant to this process closing the file and remove that
 145 * dnotify_struct.  If that was the last dnotify_struct also remove the
 146 * fsnotify_mark.
 147 */
 148void dnotify_flush(struct file *filp, fl_owner_t id)
 149{
 150        struct fsnotify_mark *fsn_mark;
 151        struct dnotify_mark *dn_mark;
 152        struct dnotify_struct *dn;
 153        struct dnotify_struct **prev;
 154        struct inode *inode;
 155        bool free = false;
 156
 157        inode = file_inode(filp);
 158        if (!S_ISDIR(inode->i_mode))
 159                return;
 160
 161        fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 162        if (!fsn_mark)
 163                return;
 164        dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 165
 166        mutex_lock(&dnotify_group->mark_mutex);
 167
 168        spin_lock(&fsn_mark->lock);
 169        prev = &dn_mark->dn;
 170        while ((dn = *prev) != NULL) {
 171                if ((dn->dn_owner == id) && (dn->dn_filp == filp)) {
 172                        *prev = dn->dn_next;
 173                        kmem_cache_free(dnotify_struct_cache, dn);
 174                        dnotify_recalc_inode_mask(fsn_mark);
 175                        break;
 176                }
 177                prev = &dn->dn_next;
 178        }
 179
 180        spin_unlock(&fsn_mark->lock);
 181
 182        /* nothing else could have found us thanks to the dnotify_groups
 183           mark_mutex */
 184        if (dn_mark->dn == NULL) {
 185                fsnotify_detach_mark(fsn_mark);
 186                free = true;
 187        }
 188
 189        mutex_unlock(&dnotify_group->mark_mutex);
 190
 191        if (free)
 192                fsnotify_free_mark(fsn_mark);
 193        fsnotify_put_mark(fsn_mark);
 194}
 195
 196/* this conversion is done only at watch creation */
 197static __u32 convert_arg(unsigned long arg)
 198{
 199        __u32 new_mask = FS_EVENT_ON_CHILD;
 200
 201        if (arg & DN_MULTISHOT)
 202                new_mask |= FS_DN_MULTISHOT;
 203        if (arg & DN_DELETE)
 204                new_mask |= (FS_DELETE | FS_MOVED_FROM);
 205        if (arg & DN_MODIFY)
 206                new_mask |= FS_MODIFY;
 207        if (arg & DN_ACCESS)
 208                new_mask |= FS_ACCESS;
 209        if (arg & DN_ATTRIB)
 210                new_mask |= FS_ATTRIB;
 211        if (arg & DN_RENAME)
 212                new_mask |= FS_DN_RENAME;
 213        if (arg & DN_CREATE)
 214                new_mask |= (FS_CREATE | FS_MOVED_TO);
 215
 216        return new_mask;
 217}
 218
 219/*
 220 * If multiple processes watch the same inode with dnotify there is only one
 221 * dnotify mark in inode->i_fsnotify_marks but we chain a dnotify_struct
 222 * onto that mark.  This function either attaches the new dnotify_struct onto
 223 * that list, or it |= the mask onto an existing dnofiy_struct.
 224 */
 225static int attach_dn(struct dnotify_struct *dn, struct dnotify_mark *dn_mark,
 226                     fl_owner_t id, int fd, struct file *filp, __u32 mask)
 227{
 228        struct dnotify_struct *odn;
 229
 230        odn = dn_mark->dn;
 231        while (odn != NULL) {
 232                /* adding more events to existing dnofiy_struct? */
 233                if ((odn->dn_owner == id) && (odn->dn_filp == filp)) {
 234                        odn->dn_fd = fd;
 235                        odn->dn_mask |= mask;
 236                        return -EEXIST;
 237                }
 238                odn = odn->dn_next;
 239        }
 240
 241        dn->dn_mask = mask;
 242        dn->dn_fd = fd;
 243        dn->dn_filp = filp;
 244        dn->dn_owner = id;
 245        dn->dn_next = dn_mark->dn;
 246        dn_mark->dn = dn;
 247
 248        return 0;
 249}
 250
 251/*
 252 * When a process calls fcntl to attach a dnotify watch to a directory it ends
 253 * up here.  Allocate both a mark for fsnotify to add and a dnotify_struct to be
 254 * attached to the fsnotify_mark.
 255 */
 256int fcntl_dirnotify(int fd, struct file *filp, unsigned long arg)
 257{
 258        struct dnotify_mark *new_dn_mark, *dn_mark;
 259        struct fsnotify_mark *new_fsn_mark, *fsn_mark;
 260        struct dnotify_struct *dn;
 261        struct inode *inode;
 262        fl_owner_t id = current->files;
 263        struct file *f;
 264        int destroy = 0, error = 0;
 265        __u32 mask;
 266
 267        /* we use these to tell if we need to kfree */
 268        new_fsn_mark = NULL;
 269        dn = NULL;
 270
 271        if (!dir_notify_enable) {
 272                error = -EINVAL;
 273                goto out_err;
 274        }
 275
 276        /* a 0 mask means we are explicitly removing the watch */
 277        if ((arg & ~DN_MULTISHOT) == 0) {
 278                dnotify_flush(filp, id);
 279                error = 0;
 280                goto out_err;
 281        }
 282
 283        /* dnotify only works on directories */
 284        inode = file_inode(filp);
 285        if (!S_ISDIR(inode->i_mode)) {
 286                error = -ENOTDIR;
 287                goto out_err;
 288        }
 289
 290        /* expect most fcntl to add new rather than augment old */
 291        dn = kmem_cache_alloc(dnotify_struct_cache, GFP_KERNEL);
 292        if (!dn) {
 293                error = -ENOMEM;
 294                goto out_err;
 295        }
 296
 297        /* new fsnotify mark, we expect most fcntl calls to add a new mark */
 298        new_dn_mark = kmem_cache_alloc(dnotify_mark_cache, GFP_KERNEL);
 299        if (!new_dn_mark) {
 300                error = -ENOMEM;
 301                goto out_err;
 302        }
 303
 304        /* convert the userspace DN_* "arg" to the internal FS_* defines in fsnotify */
 305        mask = convert_arg(arg);
 306
 307        /* set up the new_fsn_mark and new_dn_mark */
 308        new_fsn_mark = &new_dn_mark->fsn_mark;
 309        fsnotify_init_mark(new_fsn_mark, dnotify_group);
 310        new_fsn_mark->mask = mask;
 311        new_dn_mark->dn = NULL;
 312
 313        /* this is needed to prevent the fcntl/close race described below */
 314        mutex_lock(&dnotify_group->mark_mutex);
 315
 316        /* add the new_fsn_mark or find an old one. */
 317        fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, dnotify_group);
 318        if (fsn_mark) {
 319                dn_mark = container_of(fsn_mark, struct dnotify_mark, fsn_mark);
 320                spin_lock(&fsn_mark->lock);
 321        } else {
 322                fsnotify_add_mark_locked(new_fsn_mark, inode, NULL, 0);
 323                spin_lock(&new_fsn_mark->lock);
 324                fsn_mark = new_fsn_mark;
 325                dn_mark = new_dn_mark;
 326                /* we used new_fsn_mark, so don't free it */
 327                new_fsn_mark = NULL;
 328        }
 329
 330        rcu_read_lock();
 331        f = fcheck(fd);
 332        rcu_read_unlock();
 333
 334        /* if (f != filp) means that we lost a race and another task/thread
 335         * actually closed the fd we are still playing with before we grabbed
 336         * the dnotify_groups mark_mutex and fsn_mark->lock.  Since closing the
 337         * fd is the only time we clean up the marks we need to get our mark
 338         * off the list. */
 339        if (f != filp) {
 340                /* if we added ourselves, shoot ourselves, it's possible that
 341                 * the flush actually did shoot this fsn_mark.  That's fine too
 342                 * since multiple calls to destroy_mark is perfectly safe, if
 343                 * we found a dn_mark already attached to the inode, just sod
 344                 * off silently as the flush at close time dealt with it.
 345                 */
 346                if (dn_mark == new_dn_mark)
 347                        destroy = 1;
 348                goto out;
 349        }
 350
 351        __f_setown(filp, task_pid(current), PIDTYPE_PID, 0);
 352
 353        error = attach_dn(dn, dn_mark, id, fd, filp, mask);
 354        /* !error means that we attached the dn to the dn_mark, so don't free it */
 355        if (!error)
 356                dn = NULL;
 357        /* -EEXIST means that we didn't add this new dn and used an old one.
 358         * that isn't an error (and the unused dn should be freed) */
 359        else if (error == -EEXIST)
 360                error = 0;
 361
 362        dnotify_recalc_inode_mask(fsn_mark);
 363out:
 364        spin_unlock(&fsn_mark->lock);
 365
 366        if (destroy)
 367                fsnotify_detach_mark(fsn_mark);
 368        mutex_unlock(&dnotify_group->mark_mutex);
 369        if (destroy)
 370                fsnotify_free_mark(fsn_mark);
 371        fsnotify_put_mark(fsn_mark);
 372out_err:
 373        if (new_fsn_mark)
 374                fsnotify_put_mark(new_fsn_mark);
 375        if (dn)
 376                kmem_cache_free(dnotify_struct_cache, dn);
 377        return error;
 378}
 379
 380static int __init dnotify_init(void)
 381{
 382        dnotify_struct_cache = KMEM_CACHE(dnotify_struct, SLAB_PANIC);
 383        dnotify_mark_cache = KMEM_CACHE(dnotify_mark, SLAB_PANIC);
 384
 385        dnotify_group = fsnotify_alloc_group(&dnotify_fsnotify_ops);
 386        if (IS_ERR(dnotify_group))
 387                panic("unable to allocate fsnotify group for dnotify\n");
 388        return 0;
 389}
 390
 391module_init(dnotify_init)
 392