fsnotify.c

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/*
 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <[email protected]>
 *
 *  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/dcache.h>
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/srcu.h>

#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
#include "../mount.h"

/*
 * Clear all of the marks on an inode when it is being evicted from core
 */
void __fsnotify_inode_delete(struct inode *inode)
{
    fsnotify_clear_marks_by_inode(inode);
}
EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);

void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
{
    fsnotify_clear_marks_by_mount(mnt);
}

/*
 * Given an inode, first check if we care what happens to our children.  Inotify
 * and dnotify both tell their parents about events.  If we care about any event
 * on a child we run all of our children and set a dentry flag saying that the
 * parent cares.  Thus when an event happens on a child it can quickly tell if
 * if there is a need to find a parent and send the event to the parent.
 */
void __fsnotify_update_child_dentry_flags(struct inode *inode)
{
    struct dentry *alias;
    struct hlist_node *p;
    int watched;

    if (!S_ISDIR(inode->i_mode))
        return;

    /* determine if the children should tell inode about their events */
    watched = fsnotify_inode_watches_children(inode);

    spin_lock(&inode->i_lock);
    /* run all of the dentries associated with this inode.  Since this is a
     * directory, there damn well better only be one item on this list */
    hlist_for_each_entry(alias, p, &inode->i_dentry, d_alias) {
        struct dentry *child;

        /* run all of the children of the original inode and fix their
         * d_flags to indicate parental interest (their parent is the
         * original inode) */
        spin_lock(&alias->d_lock);
        list_for_each_entry(child, &alias->d_subdirs, d_u.d_child) {
            if (!child->d_inode)
                continue;

            spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
            if (watched)
                child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
            else
                child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
            spin_unlock(&child->d_lock);
        }
        spin_unlock(&alias->d_lock);
    }
    spin_unlock(&inode->i_lock);
}

/* Notify this dentry's parent about a child's events. */
int __fsnotify_parent(struct path *path, struct dentry *dentry, __u32 mask)
{
    struct dentry *parent;
    struct inode *p_inode;
    int ret = 0;

    if (!dentry)
        dentry = path->dentry;

    if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
        return 0;

    parent = dget_parent(dentry);
    p_inode = parent->d_inode;

    if (unlikely(!fsnotify_inode_watches_children(p_inode)))
        __fsnotify_update_child_dentry_flags(p_inode);
    else if (p_inode->i_fsnotify_mask & mask) {
        /* we are notifying a parent so come up with the new mask which
         * specifies these are events which came from a child. */
        mask |= FS_EVENT_ON_CHILD;

        if (path)
            ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
                       dentry->d_name.name, 0);
        else
            ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
                       dentry->d_name.name, 0);
    }

    dput(parent);

    return ret;
}
EXPORT_SYMBOL_GPL(__fsnotify_parent);

static int send_to_group(struct inode *to_tell,
             struct fsnotify_mark *inode_mark,
             struct fsnotify_mark *vfsmount_mark,
             __u32 mask, void *data,
             int data_is, u32 cookie,
             const unsigned char *file_name,
             struct fsnotify_event **event)
{
    struct fsnotify_group *group = NULL;
    __u32 inode_test_mask = 0;
    __u32 vfsmount_test_mask = 0;

    if (unlikely(!inode_mark && !vfsmount_mark)) {
        BUG();
        return 0;
    }

    /* clear ignored on inode modification */
    if (mask & FS_MODIFY) {
        if (inode_mark &&
            !(inode_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
            inode_mark->ignored_mask = 0;
        if (vfsmount_mark &&
            !(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
            vfsmount_mark->ignored_mask = 0;
    }

    /* does the inode mark tell us to do something? */
    if (inode_mark) {
        group = inode_mark->group;
        inode_test_mask = (mask & ~FS_EVENT_ON_CHILD);
        inode_test_mask &= inode_mark->mask;
        inode_test_mask &= ~inode_mark->ignored_mask;
    }

    /* does the vfsmount_mark tell us to do something? */
    if (vfsmount_mark) {
        vfsmount_test_mask = (mask & ~FS_EVENT_ON_CHILD);
        group = vfsmount_mark->group;
        vfsmount_test_mask &= vfsmount_mark->mask;
        vfsmount_test_mask &= ~vfsmount_mark->ignored_mask;
        if (inode_mark)
            vfsmount_test_mask &= ~inode_mark->ignored_mask;
    }

    pr_debug("%s: group=%p to_tell=%p mask=%x inode_mark=%p"
         " inode_test_mask=%x vfsmount_mark=%p vfsmount_test_mask=%x"
         " data=%p data_is=%d cookie=%d event=%p\n",
         __func__, group, to_tell, mask, inode_mark,
         inode_test_mask, vfsmount_mark, vfsmount_test_mask, data,
         data_is, cookie, *event);

    if (!inode_test_mask && !vfsmount_test_mask)
        return 0;

    if (group->ops->should_send_event(group, to_tell, inode_mark,
                      vfsmount_mark, mask, data,
                      data_is) == false)
        return 0;

    if (!*event) {
        *event = fsnotify_create_event(to_tell, mask, data,
                        data_is, file_name,
                        cookie, GFP_KERNEL);
        if (!*event)
            return -ENOMEM;
    }
    return group->ops->handle_event(group, inode_mark, vfsmount_mark, *event);
}

/*
 * This is the main call to fsnotify.  The VFS calls into hook specific functions
 * in linux/fsnotify.h.  Those functions then in turn call here.  Here will call
 * out to all of the registered fsnotify_group.  Those groups can then use the
 * notification event in whatever means they feel necessary.
 */
int fsnotify(struct inode *to_tell, __u32 mask, void *data, int data_is,
         const unsigned char *file_name, u32 cookie)
{
    struct hlist_node *inode_node = NULL, *vfsmount_node = NULL;
    struct fsnotify_mark *inode_mark = NULL, *vfsmount_mark = NULL;
    struct fsnotify_group *inode_group, *vfsmount_group;
    struct fsnotify_event *event = NULL;
    struct mount *mnt;
    int idx, ret = 0;
    /* global tests shouldn't care about events on child only the specific event */
    __u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);

    if (data_is == FSNOTIFY_EVENT_PATH)
        mnt = real_mount(((struct path *)data)->mnt);
    else
        mnt = NULL;

    /*
     * if this is a modify event we may need to clear the ignored masks
     * otherwise return if neither the inode nor the vfsmount care about
     * this type of event.
     */
    if (!(mask & FS_MODIFY) &&
        !(test_mask & to_tell->i_fsnotify_mask) &&
        !(mnt && test_mask & mnt->mnt_fsnotify_mask))
        return 0;

    idx = srcu_read_lock(&fsnotify_mark_srcu);

    if ((mask & FS_MODIFY) ||
        (test_mask & to_tell->i_fsnotify_mask))
        inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
                          &fsnotify_mark_srcu);

    if (mnt && ((mask & FS_MODIFY) ||
            (test_mask & mnt->mnt_fsnotify_mask))) {
        vfsmount_node = srcu_dereference(mnt->mnt_fsnotify_marks.first,
                         &fsnotify_mark_srcu);
        inode_node = srcu_dereference(to_tell->i_fsnotify_marks.first,
                          &fsnotify_mark_srcu);
    }

    while (inode_node || vfsmount_node) {
        inode_group = vfsmount_group = NULL;

        if (inode_node) {
            inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
                         struct fsnotify_mark, i.i_list);
            inode_group = inode_mark->group;
        }

        if (vfsmount_node) {
            vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
                            struct fsnotify_mark, m.m_list);
            vfsmount_group = vfsmount_mark->group;
        }

        if (inode_group > vfsmount_group) {
            /* handle inode */
            ret = send_to_group(to_tell, inode_mark, NULL, mask, data,
                        data_is, cookie, file_name, &event);
            /* we didn't use the vfsmount_mark */
            vfsmount_group = NULL;
        } else if (vfsmount_group > inode_group) {
            ret = send_to_group(to_tell, NULL, vfsmount_mark, mask, data,
                        data_is, cookie, file_name, &event);
            inode_group = NULL;
        } else {
            ret = send_to_group(to_tell, inode_mark, vfsmount_mark,
                        mask, data, data_is, cookie, file_name,
                        &event);
        }

        if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
            goto out;

        if (inode_group)
            inode_node = srcu_dereference(inode_node->next,
                              &fsnotify_mark_srcu);
        if (vfsmount_group)
            vfsmount_node = srcu_dereference(vfsmount_node->next,
                             &fsnotify_mark_srcu);
    }
    ret = 0;
out:
    srcu_read_unlock(&fsnotify_mark_srcu, idx);
    /*
     * fsnotify_create_event() took a reference so the event can't be cleaned
     * up while we are still trying to add it to lists, drop that one.
     */
    if (event)
        fsnotify_put_event(event);

    return ret;
}
EXPORT_SYMBOL_GPL(fsnotify);

static __init int fsnotify_init(void)
{
    int ret;

    BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);

    ret = init_srcu_struct(&fsnotify_mark_srcu);
    if (ret)
        panic("initializing fsnotify_mark_srcu");

    return 0;
}
core_initcall(fsnotify_init);