Re: [PATCH 15/19] vfs: Add superblock notifications [ver #16]
From: Jann Horn <jannh@google.com>
Date: 2020-02-19 23:08:40
Also in:
linux-fsdevel, lkml
On Tue, Feb 18, 2020 at 6:07 PM David Howells [off-list ref] wrote:
Add a superblock event notification facility whereby notifications about superblock events, such as I/O errors (EIO), quota limits being hit (EDQUOT) and running out of space (ENOSPC) can be reported to a monitoring process asynchronously. Note that this does not cover vfsmount topology changes. watch_mount() is used for that.
[...]
quoted hunk ↗ jump to hunk
@@ -354,6 +356,10 @@ void deactivate_locked_super(struct super_block *s) { struct file_system_type *fs = s->s_type; if (atomic_dec_and_test(&s->s_active)) { +#ifdef CONFIG_SB_NOTIFICATIONS + if (s->s_watchers) + remove_watch_list(s->s_watchers, s->s_unique_id); +#endif cleancache_invalidate_fs(s); unregister_shrinker(&s->s_shrink); fs->kill_sb(s);
[...]
+/**
+ * sys_watch_sb - Watch for superblock events.
+ * @dfd: Base directory to pathwalk from or fd referring to superblock.
+ * @filename: Path to superblock to place the watch upon
+ * @at_flags: Pathwalk control flags
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE5(watch_sb,
+ int, dfd,
+ const char __user *, filename,
+ unsigned int, at_flags,
+ int, watch_fd,
+ int, watch_id)
+{
+ struct watch_queue *wqueue;
+ struct super_block *s;
+ struct watch_list *wlist = NULL;
+ struct watch *watch = NULL;
+ struct path path;
+ unsigned int lookup_flags =
+ LOOKUP_DIRECTORY | LOOKUP_FOLLOW | LOOKUP_AUTOMOUNT;
+ int ret;[...]
+ wqueue = get_watch_queue(watch_fd);
+ if (IS_ERR(wqueue))
+ goto err_path;
+
+ s = path.dentry->d_sb;
+ if (watch_id >= 0) {
+ ret = -ENOMEM;
+ if (!s->s_watchers) {READ_ONCE() ?
+ wlist = kzalloc(sizeof(*wlist), GFP_KERNEL);
+ if (!wlist)
+ goto err_wqueue;
+ init_watch_list(wlist, NULL);
+ }
+
+ watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+ if (!watch)
+ goto err_wlist;
+
+ init_watch(watch, wqueue);
+ watch->id = s->s_unique_id;
+ watch->private = s;
+ watch->info_id = (u32)watch_id << 24;
+
+ ret = security_watch_sb(watch, s);
+ if (ret < 0)
+ goto err_watch;
+
+ down_write(&s->s_umount);
+ ret = -EIO;
+ if (atomic_read(&s->s_active)) {
+ if (!s->s_watchers) {
+ s->s_watchers = wlist;
+ wlist = NULL;
+ }
+
+ ret = add_watch_to_object(watch, s->s_watchers);
+ if (ret == 0) {
+ spin_lock(&sb_lock);
+ s->s_count++;
+ spin_unlock(&sb_lock);Where is the corresponding decrement of s->s_count? I'm guessing that it should be in the ->release_watch() handler, except that there isn't one...
+ watch = NULL;
+ }
+ }
+ up_write(&s->s_umount);
+ } else {
+ ret = -EBADSLT;
+ if (READ_ONCE(s->s_watchers)) {(Nit: I don't get why you do a lockless check here before taking the lock - it'd be more straightforward to take the lock first, and it's not like you want to optimize for the case where someone calls sys_watch_sb() with invalid arguments...)
+ down_write(&s->s_umount); + ret = remove_watch_from_object(s->s_watchers, wqueue, + s->s_unique_id, false); + up_write(&s->s_umount); + } + } + +err_watch: + kfree(watch); +err_wlist: + kfree(wlist); +err_wqueue: + put_watch_queue(wqueue); +err_path: + path_put(&path); + return ret; +} +#endif
[...]
+/**
+ * notify_sb: Post simple superblock notification.
+ * @s: The superblock the notification is about.
+ * @subtype: The type of notification.
+ * @info: WATCH_INFO_FLAG_* flags to be set in the record.
+ */
+static inline void notify_sb(struct super_block *s,
+ enum superblock_notification_type subtype,
+ u32 info)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+ if (unlikely(s->s_watchers)) {READ_ONCE() ?
+ struct superblock_notification n = {
+ .watch.type = WATCH_TYPE_SB_NOTIFY,
+ .watch.subtype = subtype,
+ .watch.info = watch_sizeof(n) | info,
+ .sb_id = s->s_unique_id,
+ };
+
+ post_sb_notification(s, &n);
+ }
+
+#endif
+}
+
+/**
+ * notify_sb_error: Post superblock error notification.
+ * @s: The superblock the notification is about.
+ * @error: The error number to be recorded.
+ */
+static inline int notify_sb_error(struct super_block *s, int error)
+{
+#ifdef CONFIG_SB_NOTIFICATIONS
+ if (unlikely(s->s_watchers)) {READ_ONCE() ?
+ struct superblock_error_notification n = {
+ .s.watch.type = WATCH_TYPE_SB_NOTIFY,
+ .s.watch.subtype = NOTIFY_SUPERBLOCK_ERROR,
+ .s.watch.info = watch_sizeof(n),
+ .s.sb_id = s->s_unique_id,
+ .error_number = error,
+ .error_cookie = 0,
+ };
+
+ post_sb_notification(s, &n.s);
+ }
+#endif
+ return error;
+}