2009-05-21 23:01:26 +02:00
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/*
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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/*
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* fsnotify inode mark locking/lifetime/and refcnting
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*
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* REFCNT:
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* The mark->refcnt tells how many "things" in the kernel currently are
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* referencing this object. The object typically will live inside the kernel
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* with a refcnt of 2, one for each list it is on (i_list, g_list). Any task
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* which can find this object holding the appropriete locks, can take a reference
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* and the object itself is guarenteed to survive until the reference is dropped.
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*
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* LOCKING:
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* There are 3 spinlocks involved with fsnotify inode marks and they MUST
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* be taken in order as follows:
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*
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* entry->lock
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* group->mark_lock
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* inode->i_lock
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*
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* entry->lock protects 2 things, entry->group and entry->inode. You must hold
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* that lock to dereference either of these things (they could be NULL even with
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* the lock)
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*
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* group->mark_lock protects the mark_entries list anchored inside a given group
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* and each entry is hooked via the g_list. It also sorta protects the
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* free_g_list, which when used is anchored by a private list on the stack of the
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* task which held the group->mark_lock.
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*
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* inode->i_lock protects the i_fsnotify_mark_entries list anchored inside a
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* given inode and each entry is hooked via the i_list. (and sorta the
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* free_i_list)
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*
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*
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* LIFETIME:
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* Inode marks survive between when they are added to an inode and when their
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* refcnt==0.
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*
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* The inode mark can be cleared for a number of different reasons including:
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* - The inode is unlinked for the last time. (fsnotify_inode_remove)
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* - The inode is being evicted from cache. (fsnotify_inode_delete)
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* - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
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* - Something explicitly requests that it be removed. (fsnotify_destroy_mark_by_entry)
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* - The fsnotify_group associated with the mark is going away and all such marks
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* need to be cleaned up. (fsnotify_clear_marks_by_group)
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*
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* Worst case we are given an inode and need to clean up all the marks on that
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* inode. We take i_lock and walk the i_fsnotify_mark_entries safely. For each
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* mark on the list we take a reference (so the mark can't disappear under us).
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* We remove that mark form the inode's list of marks and we add this mark to a
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* private list anchored on the stack using i_free_list; At this point we no
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* longer fear anything finding the mark using the inode's list of marks.
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*
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* We can safely and locklessly run the private list on the stack of everything
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* we just unattached from the original inode. For each mark on the private list
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* we grab the mark-> and can thus dereference mark->group and mark->inode. If
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* we see the group and inode are not NULL we take those locks. Now holding all
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* 3 locks we can completely remove the mark from other tasks finding it in the
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* future. Remember, 10 things might already be referencing this mark, but they
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* better be holding a ref. We drop our reference we took before we unhooked it
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* from the inode. When the ref hits 0 we can free the mark.
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*
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* Very similarly for freeing by group, except we use free_g_list.
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*
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* This has the very interesting property of being able to run concurrently with
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* any (or all) other directions.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <asm/atomic.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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void fsnotify_get_mark(struct fsnotify_mark_entry *entry)
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{
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atomic_inc(&entry->refcnt);
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}
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void fsnotify_put_mark(struct fsnotify_mark_entry *entry)
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{
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if (atomic_dec_and_test(&entry->refcnt))
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entry->free_mark(entry);
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}
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/*
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* Recalculate the mask of events relevant to a given inode locked.
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*/
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static void fsnotify_recalc_inode_mask_locked(struct inode *inode)
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{
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struct fsnotify_mark_entry *entry;
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struct hlist_node *pos;
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__u32 new_mask = 0;
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assert_spin_locked(&inode->i_lock);
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hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list)
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new_mask |= entry->mask;
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inode->i_fsnotify_mask = new_mask;
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}
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/*
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* Recalculate the inode->i_fsnotify_mask, or the mask of all FS_* event types
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* any notifier is interested in hearing for this inode.
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*/
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void fsnotify_recalc_inode_mask(struct inode *inode)
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{
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spin_lock(&inode->i_lock);
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fsnotify_recalc_inode_mask_locked(inode);
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spin_unlock(&inode->i_lock);
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2009-05-21 23:01:29 +02:00
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__fsnotify_update_child_dentry_flags(inode);
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2009-05-21 23:01:26 +02:00
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}
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/*
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* Any time a mark is getting freed we end up here.
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* The caller had better be holding a reference to this mark so we don't actually
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* do the final put under the entry->lock
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*/
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void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry)
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{
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struct fsnotify_group *group;
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struct inode *inode;
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spin_lock(&entry->lock);
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group = entry->group;
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inode = entry->inode;
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BUG_ON(group && !inode);
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BUG_ON(!group && inode);
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/* if !group something else already marked this to die */
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if (!group) {
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spin_unlock(&entry->lock);
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return;
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}
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/* 1 from caller and 1 for being on i_list/g_list */
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BUG_ON(atomic_read(&entry->refcnt) < 2);
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spin_lock(&group->mark_lock);
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spin_lock(&inode->i_lock);
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hlist_del_init(&entry->i_list);
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entry->inode = NULL;
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list_del_init(&entry->g_list);
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entry->group = NULL;
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fsnotify_put_mark(entry); /* for i_list and g_list */
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/*
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* this mark is now off the inode->i_fsnotify_mark_entries list and we
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* hold the inode->i_lock, so this is the perfect time to update the
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* inode->i_fsnotify_mask
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*/
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fsnotify_recalc_inode_mask_locked(inode);
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spin_unlock(&inode->i_lock);
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spin_unlock(&group->mark_lock);
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spin_unlock(&entry->lock);
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/*
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* Some groups like to know that marks are being freed. This is a
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* callback to the group function to let it know that this entry
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* is being freed.
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*/
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group->ops->freeing_mark(entry, group);
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2009-05-21 23:01:29 +02:00
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/*
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* __fsnotify_update_child_dentry_flags(inode);
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*
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* I really want to call that, but we can't, we have no idea if the inode
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* still exists the second we drop the entry->lock.
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*
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* The next time an event arrive to this inode from one of it's children
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* __fsnotify_parent will see that the inode doesn't care about it's
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* children and will update all of these flags then. So really this
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* is just a lazy update (and could be a perf win...)
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*/
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2009-05-21 23:01:26 +02:00
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/*
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* it's possible that this group tried to destroy itself, but this
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* this mark was simultaneously being freed by inode. If that's the
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* case, we finish freeing the group here.
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*/
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if (unlikely(atomic_dec_and_test(&group->num_marks)))
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fsnotify_final_destroy_group(group);
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}
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/*
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* Given a group, destroy all of the marks associated with that group.
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*/
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void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
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{
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struct fsnotify_mark_entry *lentry, *entry;
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LIST_HEAD(free_list);
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spin_lock(&group->mark_lock);
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list_for_each_entry_safe(entry, lentry, &group->mark_entries, g_list) {
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list_add(&entry->free_g_list, &free_list);
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list_del_init(&entry->g_list);
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fsnotify_get_mark(entry);
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}
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spin_unlock(&group->mark_lock);
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list_for_each_entry_safe(entry, lentry, &free_list, free_g_list) {
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fsnotify_destroy_mark_by_entry(entry);
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fsnotify_put_mark(entry);
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}
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}
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/*
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* Given an inode, destroy all of the marks associated with that inode.
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*/
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void fsnotify_clear_marks_by_inode(struct inode *inode)
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{
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struct fsnotify_mark_entry *entry, *lentry;
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struct hlist_node *pos, *n;
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LIST_HEAD(free_list);
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spin_lock(&inode->i_lock);
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hlist_for_each_entry_safe(entry, pos, n, &inode->i_fsnotify_mark_entries, i_list) {
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list_add(&entry->free_i_list, &free_list);
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hlist_del_init(&entry->i_list);
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fsnotify_get_mark(entry);
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}
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spin_unlock(&inode->i_lock);
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list_for_each_entry_safe(entry, lentry, &free_list, free_i_list) {
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fsnotify_destroy_mark_by_entry(entry);
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fsnotify_put_mark(entry);
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}
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}
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/*
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* given a group and inode, find the mark associated with that combination.
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* if found take a reference to that mark and return it, else return NULL
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*/
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struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group,
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struct inode *inode)
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{
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struct fsnotify_mark_entry *entry;
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struct hlist_node *pos;
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assert_spin_locked(&inode->i_lock);
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hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list) {
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if (entry->group == group) {
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fsnotify_get_mark(entry);
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return entry;
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}
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}
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return NULL;
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}
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/*
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* Nothing fancy, just initialize lists and locks and counters.
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*/
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void fsnotify_init_mark(struct fsnotify_mark_entry *entry,
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void (*free_mark)(struct fsnotify_mark_entry *entry))
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{
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spin_lock_init(&entry->lock);
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atomic_set(&entry->refcnt, 1);
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INIT_HLIST_NODE(&entry->i_list);
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entry->group = NULL;
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entry->mask = 0;
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entry->inode = NULL;
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entry->free_mark = free_mark;
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}
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/*
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* Attach an initialized mark entry to a given group and inode.
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* These marks may be used for the fsnotify backend to determine which
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* event types should be delivered to which group and for which inodes.
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*/
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int fsnotify_add_mark(struct fsnotify_mark_entry *entry,
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struct fsnotify_group *group, struct inode *inode)
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{
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struct fsnotify_mark_entry *lentry;
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int ret = 0;
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/*
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* LOCKING ORDER!!!!
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* entry->lock
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* group->mark_lock
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* inode->i_lock
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*/
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spin_lock(&entry->lock);
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spin_lock(&group->mark_lock);
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spin_lock(&inode->i_lock);
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entry->group = group;
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entry->inode = inode;
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lentry = fsnotify_find_mark_entry(group, inode);
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if (!lentry) {
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hlist_add_head(&entry->i_list, &inode->i_fsnotify_mark_entries);
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list_add(&entry->g_list, &group->mark_entries);
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fsnotify_get_mark(entry); /* for i_list and g_list */
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atomic_inc(&group->num_marks);
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fsnotify_recalc_inode_mask_locked(inode);
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}
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spin_unlock(&inode->i_lock);
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spin_unlock(&group->mark_lock);
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spin_unlock(&entry->lock);
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if (lentry) {
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ret = -EEXIST;
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fsnotify_put_mark(lentry);
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2009-05-21 23:01:29 +02:00
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} else {
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__fsnotify_update_child_dentry_flags(inode);
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2009-05-21 23:01:26 +02:00
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}
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return ret;
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}
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