Merge tag 'vfs-6.8.cachefiles' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs

Pull vfs cachefiles updates from Christian Brauner:
 "This contains improvements for on-demand cachefiles.

  If the daemon crashes and the on-demand cachefiles fd is unexpectedly
  closed in-flight requests and subsequent read operations associated
  with the fd will fail with EIO. This causes issues in various
  scenarios as this failure is currently unrecoverable.

  The work contained in this pull request introduces a failover mode and
  enables the daemon to recover in-flight requested-related objects. A
  restarted daemon will be able to process requests as usual.

  This requires that in-flight requests are stored during daemon crash
  or while the daemon is offline. In addition, a handle to
  /dev/cachefiles needs to be stored.

  This can be done by e.g., systemd's fdstore (cf. [1]) which enables
  the restarted daemon to recover state.

  Three new states are introduced in this patchset:

   (1) CLOSE
       Object is closed by the daemon.

   (2) OPEN
       Object is open and ready for processing. IOW, the open request
       has been handled successfully.

   (3) REOPENING
       Object has been previously closed and is now reopened due to a
       read request.

  A restarted daemon can recover the /dev/cachefiles fd from systemd's
  fdstore and writes "restore" to the device. This causes the object
  state to be reset from CLOSE to REOPENING and reinitializes the
  object.

  The daemon may now handle the open request. Any in-flight operations
  are restored and handled avoiding interruptions for users"

Link: https://systemd.io/FILE_DESCRIPTOR_STORE [1]

* tag 'vfs-6.8.cachefiles' of git://git.kernel.org/pub/scm/linux/kernel/git/vfs/vfs:
  cachefiles: add restore command to recover inflight ondemand read requests
  cachefiles: narrow the scope of triggering EPOLLIN events in ondemand mode
  cachefiles: resend an open request if the read request's object is closed
  cachefiles: extract ondemand info field from cachefiles_object
  cachefiles: introduce object ondemand state

Author: torvalds

fs/cachefiles/daemon.c

@@ -77,6 +77,7 @@ static const struct cachefiles_daemon_cmd cachefiles_daemon_cmds[] = {
 	{ "tag",	cachefiles_daemon_tag		},
 #ifdef CONFIG_CACHEFILES_ONDEMAND
 	{ "copen",	cachefiles_ondemand_copen	},
+	{ "restore",	cachefiles_ondemand_restore	},
 #endif
 	{ "",		NULL				}
 };
@@ -355,14 +356,24 @@ static __poll_t cachefiles_daemon_poll(struct file *file,
 					   struct poll_table_struct *poll)
 {
 	struct cachefiles_cache *cache = file->private_data;
+	XA_STATE(xas, &cache->reqs, 0);
+	struct cachefiles_req *req;
 	__poll_t mask;
 
 	poll_wait(file, &cache->daemon_pollwq, poll);
 	mask = 0;
 
 	if (cachefiles_in_ondemand_mode(cache)) {
-		if (!xa_empty(&cache->reqs))
-			mask |= EPOLLIN;
+		if (!xa_empty(&cache->reqs)) {
+			rcu_read_lock();
+			xas_for_each_marked(&xas, req, ULONG_MAX, CACHEFILES_REQ_NEW) {
+				if (!cachefiles_ondemand_is_reopening_read(req)) {
+					mask |= EPOLLIN;
+					break;
+				}
+			}
+			rcu_read_unlock();
+		}
 	} else {
 		if (test_bit(CACHEFILES_STATE_CHANGED, &cache->flags))
 			mask |= EPOLLIN;

fs/cachefiles/interface.c

@@ -31,6 +31,11 @@ struct cachefiles_object *cachefiles_alloc_object(struct fscache_cookie *cookie)
 	if (!object)
 		return NULL;
 
+	if (cachefiles_ondemand_init_obj_info(object, volume)) {
+		kmem_cache_free(cachefiles_object_jar, object);
+		return NULL;
+	}
+
 	refcount_set(&object->ref, 1);
 
 	spin_lock_init(&object->lock);
@@ -88,7 +93,7 @@ void cachefiles_put_object(struct cachefiles_object *object,
 		ASSERTCMP(object->file, ==, NULL);
 
 		kfree(object->d_name);
-
+		cachefiles_ondemand_deinit_obj_info(object);
 		cache = object->volume->cache->cache;
 		fscache_put_cookie(object->cookie, fscache_cookie_put_object);
 		object->cookie = NULL;

fs/cachefiles/internal.h

@@ -44,6 +44,19 @@ struct cachefiles_volume {
 	struct dentry			*fanout[256];	/* Fanout subdirs */
 };
 
+enum cachefiles_object_state {
+	CACHEFILES_ONDEMAND_OBJSTATE_CLOSE, /* Anonymous fd closed by daemon or initial state */
+	CACHEFILES_ONDEMAND_OBJSTATE_OPEN, /* Anonymous fd associated with object is available */
+	CACHEFILES_ONDEMAND_OBJSTATE_REOPENING, /* Object that was closed and is being reopened. */
+};
+
+struct cachefiles_ondemand_info {
+	struct work_struct		ondemand_work;
+	int				ondemand_id;
+	enum cachefiles_object_state	state;
+	struct cachefiles_object	*object;
+};
+
 /*
  * Backing file state.
  */
@@ -61,7 +74,7 @@ struct cachefiles_object {
 	unsigned long			flags;
 #define CACHEFILES_OBJECT_USING_TMPFILE	0		/* Have an unlinked tmpfile */
 #ifdef CONFIG_CACHEFILES_ONDEMAND
-	int				ondemand_id;
+	struct cachefiles_ondemand_info	*ondemand;
 #endif
 };
 
@@ -290,12 +303,42 @@ extern ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 extern int cachefiles_ondemand_copen(struct cachefiles_cache *cache,
 				     char *args);
 
+extern int cachefiles_ondemand_restore(struct cachefiles_cache *cache,
+					char *args);
+
 extern int cachefiles_ondemand_init_object(struct cachefiles_object *object);
 extern void cachefiles_ondemand_clean_object(struct cachefiles_object *object);
 
 extern int cachefiles_ondemand_read(struct cachefiles_object *object,
 				    loff_t pos, size_t len);
 
+extern int cachefiles_ondemand_init_obj_info(struct cachefiles_object *obj,
+					struct cachefiles_volume *volume);
+extern void cachefiles_ondemand_deinit_obj_info(struct cachefiles_object *obj);
+
+#define CACHEFILES_OBJECT_STATE_FUNCS(_state, _STATE)	\
+static inline bool								\
+cachefiles_ondemand_object_is_##_state(const struct cachefiles_object *object) \
+{												\
+	return object->ondemand->state == CACHEFILES_ONDEMAND_OBJSTATE_##_STATE; \
+}												\
+												\
+static inline void								\
+cachefiles_ondemand_set_object_##_state(struct cachefiles_object *object) \
+{												\
+	object->ondemand->state = CACHEFILES_ONDEMAND_OBJSTATE_##_STATE; \
+}
+
+CACHEFILES_OBJECT_STATE_FUNCS(open, OPEN);
+CACHEFILES_OBJECT_STATE_FUNCS(close, CLOSE);
+CACHEFILES_OBJECT_STATE_FUNCS(reopening, REOPENING);
+
+static inline bool cachefiles_ondemand_is_reopening_read(struct cachefiles_req *req)
+{
+	return cachefiles_ondemand_object_is_reopening(req->object) &&
+			req->msg.opcode == CACHEFILES_OP_READ;
+}
+
 #else
 static inline ssize_t cachefiles_ondemand_daemon_read(struct cachefiles_cache *cache,
 					char __user *_buffer, size_t buflen)
@@ -317,6 +360,20 @@ static inline int cachefiles_ondemand_read(struct cachefiles_object *object,
 {
 	return -EOPNOTSUPP;
 }
+
+static inline int cachefiles_ondemand_init_obj_info(struct cachefiles_object *obj,
+						struct cachefiles_volume *volume)
+{
+	return 0;
+}
+static inline void cachefiles_ondemand_deinit_obj_info(struct cachefiles_object *obj)
+{
+}
+
+static inline bool cachefiles_ondemand_is_reopening_read(struct cachefiles_req *req)
+{
+	return false;
+}
 #endif
 
 /*