fsnotify: split generic and inode specific mark code

currently all marking is done by functions in inode-mark.c.  Some of this
is pretty generic and should be instead done in a generic function and we
should only put the inode specific code in inode-mark.c

Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 294 insertions, 0 deletions

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
new file mode 100644
index 000000000000..e56e8768d676
--- /dev/null
+++ b/fs/notify/mark.c
@@ -0,0 +1,294 @@
+/*
+ *  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.
+ */
+
+/*
+ * fsnotify inode mark locking/lifetime/and refcnting
+ *
+ * REFCNT:
+ * The mark->refcnt tells how many "things" in the kernel currently are
+ * referencing this object.  The object typically will live inside the kernel
+ * with a refcnt of 2, one for each list it is on (i_list, g_list).  Any task
+ * which can find this object holding the appropriete locks, can take a reference
+ * and the object itself is guarenteed to survive until the reference is dropped.
+ *
+ * LOCKING:
+ * There are 3 spinlocks involved with fsnotify inode marks and they MUST
+ * be taken in order as follows:
+ *
+ * mark->lock
+ * group->mark_lock
+ * inode->i_lock
+ *
+ * mark->lock protects 2 things, mark->group and mark->inode.  You must hold
+ * that lock to dereference either of these things (they could be NULL even with
+ * the lock)
+ *
+ * group->mark_lock protects the marks_list anchored inside a given group
+ * and each mark is hooked via the g_list.  It also sorta protects the
+ * free_g_list, which when used is anchored by a private list on the stack of the
+ * task which held the group->mark_lock.
+ *
+ * inode->i_lock protects the i_fsnotify_marks list anchored inside a
+ * given inode and each mark is hooked via the i_list. (and sorta the
+ * free_i_list)
+ *
+ *
+ * LIFETIME:
+ * Inode marks survive between when they are added to an inode and when their
+ * refcnt==0.
+ *
+ * The inode mark can be cleared for a number of different reasons including:
+ * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
+ * - The inode is being evicted from cache. (fsnotify_inode_delete)
+ * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
+ * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
+ * - The fsnotify_group associated with the mark is going away and all such marks
+ *   need to be cleaned up. (fsnotify_clear_marks_by_group)
+ *
+ * Worst case we are given an inode and need to clean up all the marks on that
+ * inode.  We take i_lock and walk the i_fsnotify_marks safely.  For each
+ * mark on the list we take a reference (so the mark can't disappear under us).
+ * We remove that mark form the inode's list of marks and we add this mark to a
+ * private list anchored on the stack using i_free_list;  At this point we no
+ * longer fear anything finding the mark using the inode's list of marks.
+ *
+ * We can safely and locklessly run the private list on the stack of everything
+ * we just unattached from the original inode.  For each mark on the private list
+ * we grab the mark-> and can thus dereference mark->group and mark->inode.  If
+ * we see the group and inode are not NULL we take those locks.  Now holding all
+ * 3 locks we can completely remove the mark from other tasks finding it in the
+ * future.  Remember, 10 things might already be referencing this mark, but they
+ * better be holding a ref.  We drop our reference we took before we unhooked it
+ * from the inode.  When the ref hits 0 we can free the mark.
+ *
+ * Very similarly for freeing by group, except we use free_g_list.
+ *
+ * This has the very interesting property of being able to run concurrently with
+ * any (or all) other directions.
+ */
+
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/slab.h>
+#include <linux/spinlock.h>
+#include <linux/writeback.h> /* for inode_lock */
+
+#include <asm/atomic.h>
+
+#include <linux/fsnotify_backend.h>
+#include "fsnotify.h"
+
+void fsnotify_get_mark(struct fsnotify_mark *mark)
+{
+        atomic_inc(&mark->refcnt);
+}
+
+void fsnotify_put_mark(struct fsnotify_mark *mark)
+{
+        if (atomic_dec_and_test(&mark->refcnt))
+                mark->free_mark(mark);
+}
+
+/*
+ * Any time a mark is getting freed we end up here.
+ * The caller had better be holding a reference to this mark so we don't actually
+ * do the final put under the mark->lock
+ */
+void fsnotify_destroy_mark(struct fsnotify_mark *mark)
+{
+        struct fsnotify_group *group;
+        struct inode *inode;
+
+        spin_lock(&mark->lock);
+
+        group = mark->group;
+        inode = mark->i.inode;
+
+        BUG_ON(group && !inode);
+        BUG_ON(!group && inode);
+
+        /* if !group something else already marked this to die */
+        if (!group) {
+                spin_unlock(&mark->lock);
+                return;
+        }
+
+        /* 1 from caller and 1 for being on i_list/g_list */
+        BUG_ON(atomic_read(&mark->refcnt) < 2);
+
+        spin_lock(&group->mark_lock);
+
+        if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
+                fsnotify_destroy_inode_mark(mark);
+        else
+                BUG();
+
+        list_del_init(&mark->g_list);
+        mark->group = NULL;
+
+        fsnotify_put_mark(mark); /* for i_list and g_list */
+
+        spin_unlock(&group->mark_lock);
+        spin_unlock(&mark->lock);
+
+        /*
+         * Some groups like to know that marks are being freed.  This is a
+         * callback to the group function to let it know that this mark
+         * is being freed.
+         */
+        if (group->ops->freeing_mark)
+                group->ops->freeing_mark(mark, group);
+
+        /*
+         * __fsnotify_update_child_dentry_flags(inode);
+         *
+         * I really want to call that, but we can't, we have no idea if the inode
+         * still exists the second we drop the mark->lock.
+         *
+         * The next time an event arrive to this inode from one of it's children
+         * __fsnotify_parent will see that the inode doesn't care about it's
+         * children and will update all of these flags then.  So really this
+         * is just a lazy update (and could be a perf win...)
+         */
+
+
+        iput(inode);
+
+        /*
+         * it's possible that this group tried to destroy itself, but this
+         * this mark was simultaneously being freed by inode.  If that's the
+         * case, we finish freeing the group here.
+         */
+        if (unlikely(atomic_dec_and_test(&group->num_marks)))
+                fsnotify_final_destroy_group(group);
+}
+
+/*
+ * Attach an initialized mark to a given group and fs object.
+ * These marks may be used for the fsnotify backend to determine which
+ * event types should be delivered to which group.
+ */
+int fsnotify_add_mark(struct fsnotify_mark *mark,
+                      struct fsnotify_group *group, struct inode *inode,
+                      struct vfsmount *mnt, int allow_dups)
+{
+        int ret = 0;
+
+        BUG_ON(mnt);
+        BUG_ON(inode && mnt);
+        BUG_ON(!inode && !mnt);
+
+        /*
+         * if this group isn't being testing for inode type events we need
+         * to start testing
+         */
+        if (inode && unlikely(list_empty(&group->inode_group_list)))
+                fsnotify_add_inode_group(group);
+        else if (mnt && unlikely(list_empty(&group->vfsmount_group_list)))
+                fsnotify_add_vfsmount_group(group);
+
+        /*
+         * LOCKING ORDER!!!!
+         * mark->lock
+         * group->mark_lock
+         * inode->i_lock
+         */
+        spin_lock(&mark->lock);
+        spin_lock(&group->mark_lock);
+
+        mark->group = group;
+        list_add(&mark->g_list, &group->marks_list);
+        atomic_inc(&group->num_marks);
+        fsnotify_get_mark(mark); /* for i_list and g_list */
+
+        if (inode) {
+                ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
+                if (ret)
+                        goto err;
+        } else {
+                BUG();
+        }
+
+        spin_unlock(&group->mark_lock);
+        spin_unlock(&mark->lock);
+
+        if (inode)
+                __fsnotify_update_child_dentry_flags(inode);
+
+        return ret;
+err:
+        mark->group = NULL;
+        list_del_init(&mark->g_list);
+        atomic_dec(&group->num_marks);
+        fsnotify_put_mark(mark);
+
+        spin_unlock(&group->mark_lock);
+        spin_unlock(&mark->lock);
+
+        return ret;
+}
+
+/*
+ * Given a group, destroy all of the marks associated with that group.
+ */
+void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
+{
+        struct fsnotify_mark *lmark, *mark;
+        LIST_HEAD(free_list);
+
+        spin_lock(&group->mark_lock);
+        list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
+                list_add(&mark->free_g_list, &free_list);
+                list_del_init(&mark->g_list);
+                fsnotify_get_mark(mark);
+        }
+        spin_unlock(&group->mark_lock);
+
+        list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) {
+                fsnotify_destroy_mark(mark);
+                fsnotify_put_mark(mark);
+        }
+}
+
+void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
+{
+        assert_spin_locked(&old->lock);
+        new->i.inode = old->i.inode;
+        new->m.mnt = old->m.mnt;
+        new->group = old->group;
+        new->mask = old->mask;
+        new->free_mark = old->free_mark;
+}
+
+/*
+ * Nothing fancy, just initialize lists and locks and counters.
+ */
+void fsnotify_init_mark(struct fsnotify_mark *mark,
+                        void (*free_mark)(struct fsnotify_mark *mark))
+{
+        spin_lock_init(&mark->lock);
+        atomic_set(&mark->refcnt, 1);
+        INIT_HLIST_NODE(&mark->i.i_list);
+        mark->group = NULL;
+        mark->mask = 0;
+        mark->i.inode = NULL;
+        mark->free_mark = free_mark;
+}