/* * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2, or (at your option) * any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; see the file COPYING. If not, write to * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ #include <linux/list.h> #include <linux/mutex.h> #include <linux/slab.h> #include <linux/srcu.h> #include <linux/rculist.h> #include <linux/wait.h> #include <linux/fsnotify_backend.h> #include "fsnotify.h" #include <asm/atomic.h> /* protects writes to fsnotify_groups and fsnotify_mask */ static DEFINE_MUTEX(fsnotify_grp_mutex); /* protects reads while running the fsnotify_groups list */ struct srcu_struct fsnotify_grp_srcu; /* all groups registered to receive filesystem notifications */ LIST_HEAD(fsnotify_groups); /* bitwise OR of all events (FS_*) interesting to some group on this system */ __u32 fsnotify_mask; /* * When a new group registers or changes it's set of interesting events * this function updates the fsnotify_mask to contain all interesting events */ void fsnotify_recalc_global_mask(void) { struct fsnotify_group *group; __u32 mask = 0; int idx; idx = srcu_read_lock(&fsnotify_grp_srcu); list_for_each_entry_rcu(group, &fsnotify_groups, group_list) mask |= group->mask; srcu_read_unlock(&fsnotify_grp_srcu, idx); fsnotify_mask = mask; } /* * Update the group->mask by running all of the marks associated with this * group and finding the bitwise | of all of the mark->mask. If we change * the group->mask we need to update the global mask of events interesting * to the system. */ void fsnotify_recalc_group_mask(struct fsnotify_group *group) { __u32 mask = 0; __u32 old_mask = group->mask; struct fsnotify_mark_entry *entry; spin_lock(&group->mark_lock); list_for_each_entry(entry, &group->mark_entries, g_list) mask |= entry->mask; spin_unlock(&group->mark_lock); group->mask = mask; if (old_mask != mask) fsnotify_recalc_global_mask(); } /* * Take a reference to a group so things found under the fsnotify_grp_mutex * can't get freed under us */ static void fsnotify_get_group(struct fsnotify_group *group) { atomic_inc(&group->refcnt); } /* * Final freeing of a group */ void fsnotify_final_destroy_group(struct fsnotify_group *group) { /* clear the notification queue of all events */ fsnotify_flush_notify(group); if (group->ops->free_group_priv) group->ops->free_group_priv(group); kfree(group); } /* * Trying to get rid of a group. We need to first get rid of any outstanding * allocations and then free the group. Remember that fsnotify_clear_marks_by_group * could miss marks that are being freed by inode and those marks could still * hold a reference to this group (via group->num_marks) If we get into that * situtation, the fsnotify_final_destroy_group will get called when that final * mark is freed. */ static void fsnotify_destroy_group(struct fsnotify_group *group) { /* clear all inode mark entries for this group */ fsnotify_clear_marks_by_group(group); /* past the point of no return, matches the initial value of 1 */ if (atomic_dec_and_test(&group->num_marks)) fsnotify_final_destroy_group(group); } /* * Remove this group from the global list of groups that will get events * this can be done even if there are still references and things still using * this group. This just stops the group from getting new events. */ static void __fsnotify_evict_group(struct fsnotify_group *group) { BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex)); if (group->on_group_list) list_del_rcu(&group->group_list); group->on_group_list = 0; } /* * Called when a group is no longer interested in getting events. This can be * used if a group is misbehaving or if for some reason a group should no longer * get any filesystem events. */ void fsnotify_evict_group(struct fsnotify_group *group) { mutex_lock(&fsnotify_grp_mutex); __fsnotify_evict_group(group); mutex_unlock(&fsnotify_grp_mutex); } /* * Drop a reference to a group. Free it if it's through. */ void fsnotify_put_group(struct fsnotify_group *group) { if (!atomic_dec_and_mutex_lock(&group->refcnt, &fsnotify_grp_mutex)) return; /* * OK, now we know that there's no other users *and* we hold mutex, * so no new references will appear */ __fsnotify_evict_group(group); /* * now it's off the list, so the only thing we might care about is * srcu access.... */ mutex_unlock(&fsnotify_grp_mutex); synchronize_srcu(&fsnotify_grp_srcu); /* and now it is really dead. _Nothing_ could be seeing it */ fsnotify_recalc_global_mask(); fsnotify_destroy_group(group); } /* * Simply run the fsnotify_groups list and find a group which matches * the given parameters. If a group is found we take a reference to that * group. */ static struct fsnotify_group *fsnotify_find_group(unsigned int group_num, __u32 mask, const struct fsnotify_ops *ops) { struct fsnotify_group *group_iter; struct fsnotify_group *group = NULL; BUG_ON(!mutex_is_locked(&fsnotify_grp_mutex)); list_for_each_entry_rcu(group_iter, &fsnotify_groups, group_list) { if (group_iter->group_num == group_num) { if ((group_iter->mask == mask) && (group_iter->ops == ops)) { fsnotify_get_group(group_iter); group = group_iter; } else group = ERR_PTR(-EEXIST); } } return group; } /* * Either finds an existing group which matches the group_num, mask, and ops or * creates a new group and adds it to the global group list. In either case we * take a reference for the group returned. */ struct fsnotify_group *fsnotify_obtain_group(unsigned int group_num, __u32 mask, const struct fsnotify_ops *ops) { struct fsnotify_group *group, *tgroup; /* very low use, simpler locking if we just always alloc */ group = kmalloc(sizeof(struct fsnotify_group), GFP_KERNEL); if (!group) return ERR_PTR(-ENOMEM); atomic_set(&group->refcnt, 1); group->on_group_list = 0; group->group_num = group_num; group->mask = mask; mutex_init(&group->notification_mutex); INIT_LIST_HEAD(&group->notification_list); init_waitqueue_head(&group->notification_waitq); group->q_len = 0; group->max_events = UINT_MAX; spin_lock_init(&group->mark_lock); atomic_set(&group->num_marks, 0); INIT_LIST_HEAD(&group->mark_entries); group->ops = ops; mutex_lock(&fsnotify_grp_mutex); tgroup = fsnotify_find_group(group_num, mask, ops); if (tgroup) { /* group already exists */ mutex_unlock(&fsnotify_grp_mutex); /* destroy the new one we made */ fsnotify_put_group(group); return tgroup; } /* group not found, add a new one */ list_add_rcu(&group->group_list, &fsnotify_groups); group->on_group_list = 1; /* being on the fsnotify_groups list holds one num_marks */ atomic_inc(&group->num_marks); mutex_unlock(&fsnotify_grp_mutex); if (mask) fsnotify_recalc_global_mask(); return group; }