[RFC PATCH v2 7/9] fuse: add fuse device ioctl(FUSE_DEV_IOC_REINIT)

[Alexander Mikhalitsyn]

This ioctl aborts fuse connection and then reinitializes it,
sends FUSE_INIT request to allow a new userspace daemon
to pick up the fuse connection.

Cc: Miklos Szeredi <mszeredi@xxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Amir Goldstein <amir73il@xxxxxxxxx>
Cc: Stéphane Graber <stgraber@xxxxxxxxxx>
Cc: Seth Forshee <sforshee@xxxxxxxxxx>
Cc: Christian Brauner <brauner@xxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxx>
Cc: Pavel Tikhomirov <ptikhomirov@xxxxxxxxxxxxx>
Cc: Bernd Schubert <bschubert@xxxxxxx>
Cc: linux-fsdevel@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Cc: criu@xxxxxxxxxx
Signed-off-by: Alexander Mikhalitsyn <aleksandr.mikhalitsyn@xxxxxxxxxxxxx>
---
 fs/fuse/dev.c             | 152 ++++++++++++++++++++++++++++++++++++++
 fs/fuse/fuse_i.h          |   3 +
 include/uapi/linux/fuse.h |   1 +
 3 files changed, 156 insertions(+)

diff --git a/fs/fuse/dev.c b/fs/fuse/dev.c
index b4501a10c379..93a457c90b49 100644
--- a/fs/fuse/dev.c
+++ b/fs/fuse/dev.c
@@ -2187,6 +2187,132 @@ void fuse_abort_conn(struct fuse_conn *fc)
 }
 EXPORT_SYMBOL_GPL(fuse_abort_conn);
 
+static int fuse_reinit_conn(struct fuse_conn *fc)
+{
+	struct fuse_iqueue *fiq = &fc->iq;
+	struct fuse_dev *fud;
+	unsigned int i;
+
+	spin_lock(&fc->lock);
+	if (fc->reinit_in_progress) {
+		spin_unlock(&fc->lock);
+		return -EBUSY;
+	}
+
+	if (fc->conn_gen + 1 < fc->conn_gen) {
+		spin_unlock(&fc->lock);
+		return -EOVERFLOW;
+	}
+
+	fc->reinit_in_progress = true;
+	spin_unlock(&fc->lock);
+
+	/*
+	 * Unsets fc->connected and fiq->connected and
+	 * ensures that no new requests can be queued
+	 */
+	fuse_abort_conn(fc);
+	fuse_wait_aborted(fc);
+
+	spin_lock(&fc->lock);
+	if (fc->connected) {
+		fc->reinit_in_progress = false;
+		spin_unlock(&fc->lock);
+		return -EINVAL;
+	}
+
+	fc->conn_gen++;
+
+	spin_lock(&fiq->lock);
+	if (request_pending(fiq) || fiq->forget_list_tail != &fiq->forget_list_head) {
+		spin_unlock(&fiq->lock);
+		fc->reinit_in_progress = false;
+		spin_unlock(&fc->lock);
+		return -EINVAL;
+	}
+
+	if (&fuse_dev_fiq_ops != fiq->ops) {
+		spin_unlock(&fiq->lock);
+		fc->reinit_in_progress = false;
+		spin_unlock(&fc->lock);
+		return -EOPNOTSUPP;
+	}
+
+	fiq->connected = 1;
+	spin_unlock(&fiq->lock);
+
+	spin_lock(&fc->bg_lock);
+	if (!list_empty(&fc->bg_queue)) {
+		spin_unlock(&fc->bg_lock);
+		fc->reinit_in_progress = false;
+		spin_unlock(&fc->lock);
+		return -EINVAL;
+	}
+
+	fc->blocked = 0;
+	fc->max_background = FUSE_DEFAULT_MAX_BACKGROUND;
+	spin_unlock(&fc->bg_lock);
+
+	list_for_each_entry(fud, &fc->devices, entry) {
+		struct fuse_pqueue *fpq = &fud->pq;
+
+		spin_lock(&fpq->lock);
+		if (!list_empty(&fpq->io)) {
+			spin_unlock(&fpq->lock);
+			fc->reinit_in_progress = false;
+			spin_unlock(&fc->lock);
+			return -EINVAL;
+		}
+
+		for (i = 0; i < FUSE_PQ_HASH_SIZE; i++) {
+			if (!list_empty(&fpq->processing[i])) {
+				spin_unlock(&fpq->lock);
+				fc->reinit_in_progress = false;
+				spin_unlock(&fc->lock);
+				return -EINVAL;
+			}
+		}
+
+		fpq->connected = 1;
+		spin_unlock(&fpq->lock);
+	}
+
+	fuse_set_initialized(fc);
+
+	/* Background queuing checks fc->connected under bg_lock */
+	spin_lock(&fc->bg_lock);
+	fc->connected = 1;
+	spin_unlock(&fc->bg_lock);
+
+	fc->aborted = false;
+	fc->abort_err = 0;
+
+	/* nullify all the flags */
+	memset(&fc->flags, 0, sizeof(struct fuse_conn_flags));
+
+	spin_unlock(&fc->lock);
+
+	down_read(&fc->killsb);
+	if (!list_empty(&fc->mounts)) {
+		struct fuse_mount *fm;
+
+		fm = list_first_entry(&fc->mounts, struct fuse_mount, fc_entry);
+		if (!fm->sb) {
+			up_read(&fc->killsb);
+			return -EINVAL;
+		}
+
+		fuse_send_init(fm);
+	}
+	up_read(&fc->killsb);
+
+	spin_lock(&fc->lock);
+	fc->reinit_in_progress = false;
+	spin_unlock(&fc->lock);
+
+	return 0;
+}
+
 void fuse_wait_aborted(struct fuse_conn *fc)
 {
 	/* matches implicit memory barrier in fuse_drop_waiting() */
@@ -2282,6 +2408,32 @@ static long fuse_dev_ioctl(struct file *file, unsigned int cmd,
 			}
 		}
 		break;
+	case FUSE_DEV_IOC_REINIT:
+		struct fuse_conn *fc;
+
+		if (!checkpoint_restore_ns_capable(file->f_cred->user_ns))
+			return -EPERM;
+
+		res = -EINVAL;
+		fud = fuse_get_dev(file);
+
+		/*
+		 * Only fuse mounts with an already initialized fuse
+		 * connection are supported
+		 */
+		if (file->f_op == &fuse_dev_operations && fud) {
+			mutex_lock(&fuse_mutex);
+			fc = fud->fc;
+			if (fc)
+				fc = fuse_conn_get(fc);
+			mutex_unlock(&fuse_mutex);
+
+			if (fc) {
+				res = fuse_reinit_conn(fc);
+				fuse_conn_put(fc);
+			}
+		}
+		break;
 	default:
 		res = -ENOTTY;
 		break;
diff --git a/fs/fuse/fuse_i.h b/fs/fuse/fuse_i.h
index 90c5b3459864..8f2c0f969f6f 100644
--- a/fs/fuse/fuse_i.h
+++ b/fs/fuse/fuse_i.h
@@ -752,6 +752,9 @@ struct fuse_conn {
 	/** Connection aborted via sysfs */
 	bool aborted;
 
+	/** Connection reinit in progress */
+	bool reinit_in_progress;
+
 	/** Connection failed (version mismatch).  Cannot race with
 	    setting other bitfields since it is only set once in INIT
 	    reply, before any other request, and never cleared */
diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h
index b3fcab13fcd3..325da23431ef 100644
--- a/include/uapi/linux/fuse.h
+++ b/include/uapi/linux/fuse.h
@@ -992,6 +992,7 @@ struct fuse_notify_retrieve_in {
 /* Device ioctls: */
 #define FUSE_DEV_IOC_MAGIC		229
 #define FUSE_DEV_IOC_CLONE		_IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t)
+#define FUSE_DEV_IOC_REINIT		_IO(FUSE_DEV_IOC_MAGIC, 0)
 
 struct fuse_lseek_in {
 	uint64_t	fh;
-- 
2.34.1