Hi everyone!
I'm developing a kernel module and trying to setup a directory watch with fsnotify.
I mainly copied existing code paths in the kernel that I found, because I couldn't
find any usage documentation.
I am using Linux Kernel version 5.12.0.
My issue is the following:
- Setting up the watch works initially.
- If I remove and reinsert the kernel module, fsnotify_add_inode_mark fails with EEXIST.
So I must be doing something wrong. I am using the put/destroy methods for the mark
and the put method for the group when unloading the module.
Here is how I setup the watch:
> static struct fsnotify_group *group;
> static struct fsnotify_mark mark;
>
> static int setup_sync_dir_watch(char *sync_dir) {
> int ret;
> struct fsnotify_mark *old_mark;
> struct path sync_dir_path;
>
> pr_info("%s: Syncing extents for files under '%s'\n", MODULE_NAME,
> sync_dir);
>
> group = fsnotify_alloc_group(&nvmeof_xrp_fsnotify_ops);
> if (IS_ERR(group)) {
> pr_err("%s: Error allocating fsnotify group!\n", MODULE_NAME);
> return -1;
> }
> ret = kern_path(sync_dir, LOOKUP_FOLLOW, &sync_dir_path);
> if (ret) {
> pr_err("%s: Error getting kernel path: %d!\n", MODULE_NAME, ret);
> goto release_group;
> }
> fsnotify_init_mark(&mark, group);
> mark.mask = FS_CREATE | FS_DELETE | FS_MODIFY |
> FS_CLOSE_WRITE | FS_EVENT_ON_CHILD;
> ret = fsnotify_add_inode_mark(&mark,
> sync_dir_path.dentry->d_inode, 0);
> path_put(&sync_dir_path);
> if (ret) {
> pr_err("%s: Error adding fsnotify mark! Error code: %d\n", MODULE_NAME,
> ret);
> goto release_mark;
> }
> return 0;
> release_mark:
> fsnotify_destroy_mark(&mark, group);
> fsnotify_put_mark(&mark);
> release_group:
> fsnotify_put_group(group);
> return ret;
> }
And here is how I clear it when exiting the module:
> static void __exit module_exit(void) {
> fsnotify_destroy_mark(&mark, group);
> fsnotify_put_mark(&mark);
> fsnotify_put_group(group);
I also tried to find the mark and delete it, but it returns NULL even though
fsnotify_add_inode_mark returns EEXISTS:
> mutex_lock(&group->mark_mutex);
> old_mark = fsnotify_find_mark(
> &sync_dir_path.dentry->d_inode->i_fsnotify_marks,
> group);
> if (old_mark != NULL) {
> pr_info("%s: Found old mark, destroying it...\n", MODULE_NAME);
> fsnotify_destroy_mark(old_mark, group);
> fsnotify_put_mark(old_mark);
> }
> mutex_unlock(&group->mark_mutex);
Thanks in advance,
Yannis
