Add a new notification type FUSE_NOTIFY_LOCK. This notification can be sent by file server to signifiy that a previous locking request has completed and actual caller should be woken up.
As of now we don't support blocking variant of posix locks and daemon returns -EOPNOTSUPP. Reason being that it can lead to deadlocks. Virtqueue size is limited and it is possible we fill virtqueue with all the requests of fcntl(F_SETLKW) and wait for reply. And later a subsequent unlock request can't make progress because virtqueue is full. And that means F_SETLKW can't make progress and we are deadlocked. This problem is not limited to posix locks only. I think blocking remote flock and open file description locks should face the same issue. Right now fuse does not support open file description locks, so its not a problem. But fuse/virtiofs does support remote flock and they can use same mechanism too. Use notification queue to solve this problem. After submitting lock request device will send a reply asking requester to wait. Once lock is available, requester will get a notification saying lock is available. That way we don't keep the request virtueue busy while we are waiting for lock and further unlock requests can make progress. When we get a reply in response to lock request, we need a way to know if we need to wait for notification or not. I have overloaded the fuse_out_header->error field. If value is ->error is 1, that's a signal to caller to wait for lock notification. Overloading ->error in this way is not the best way to do it. But I am running out of ideas. Signed-off-by: Vivek Goyal <[email protected]> Signed-off-by: Ioannis Angelakopoulos <[email protected]> --- fs/fuse/virtio_fs.c | 73 +++++++++++++++++++++++++++++++++++++++ include/uapi/linux/fuse.h | 11 +++++- 2 files changed, 83 insertions(+), 1 deletion(-) diff --git a/fs/fuse/virtio_fs.c b/fs/fuse/virtio_fs.c index 8d33879d62fb..1634ea2d0555 100644 --- a/fs/fuse/virtio_fs.c +++ b/fs/fuse/virtio_fs.c @@ -48,6 +48,7 @@ struct virtio_fs_vq { struct virtqueue *vq; /* protected by ->lock */ struct work_struct done_work; struct list_head queued_reqs; + struct list_head wait_reqs; /* Requests waiting for notification */ struct list_head end_reqs; /* End these requests */ struct virtio_fs_notify_node *notify_nodes; struct list_head notify_reqs; /* List for queuing notify requests */ @@ -575,13 +576,72 @@ static int virtio_fs_enqueue_all_notify(struct virtio_fs_vq *fsvq) return 0; } +static int notify_complete_waiting_req(struct virtio_fs *vfs, + struct fuse_notify_lock_out *out_args) +{ + /* TODO: Handle multiqueue */ + struct virtio_fs_vq *fsvq = &vfs->vqs[vfs->first_reqq_idx]; + struct fuse_req *req, *next; + bool found = false; + + /* Find waiting request with the unique number and end it */ + spin_lock(&fsvq->lock); + list_for_each_entry_safe(req, next, &fsvq->wait_reqs, list) { + if (req->in.h.unique == out_args->unique) { + list_del_init(&req->list); + clear_bit(FR_SENT, &req->flags); + /* Transfer error code from notify */ + req->out.h.error = out_args->error; + found = true; + break; + } + } + spin_unlock(&fsvq->lock); + + /* + * TODO: It is possible that some re-ordering happens in notify + * comes before request is complete. Deal with it. + */ + if (found) { + end_req_dec_in_flight(req, fsvq); + } else + pr_debug("virtio-fs: Did not find waiting request with unique=0x%llx\n", + out_args->unique); + + return 0; +} + +static int virtio_fs_handle_notify(struct virtio_fs *vfs, + struct virtio_fs_notify *notify) +{ + int ret = 0; + struct fuse_out_header *oh = ¬ify->out_hdr; + struct fuse_notify_lock_out *lo; + + /* + * For notifications, oh.unique is 0 and oh->error contains code + * for which notification as arrived. + */ + switch (oh->error) { + case FUSE_NOTIFY_LOCK: + lo = (struct fuse_notify_lock_out *) ¬ify->outarg; + notify_complete_waiting_req(vfs, lo); + break; + default: + pr_err("virtio-fs: Unexpected notification %d\n", oh->error); + } + return ret; +} + static void virtio_fs_notify_done_work(struct work_struct *work) { struct virtio_fs_vq *fsvq = container_of(work, struct virtio_fs_vq, done_work); struct virtqueue *vq = fsvq->vq; + struct virtio_fs *vfs = vq->vdev->priv; LIST_HEAD(reqs); struct virtio_fs_notify_node *notifyn, *next; + struct fuse_out_header *oh; spin_lock(&fsvq->lock); do { @@ -597,6 +657,10 @@ static void virtio_fs_notify_done_work(struct work_struct *work) /* Process notify */ list_for_each_entry_safe(notifyn, next, &reqs, list) { + oh = ¬ifyn->notify.out_hdr; + WARN_ON(oh->unique); + /* Handle notification */ + virtio_fs_handle_notify(vfs, ¬ifyn->notify); spin_lock(&fsvq->lock); dec_in_flight_req(fsvq); list_del_init(¬ifyn->list); @@ -696,6 +760,14 @@ static void virtio_fs_request_complete(struct fuse_req *req, * TODO verify that server properly follows FUSE protocol * (oh.uniq, oh.len) */ + if (req->out.h.error == 1) { + /* Wait for notification to complete request */ + spin_lock(&fsvq->lock); + list_add_tail(&req->list, &fsvq->wait_reqs); + spin_unlock(&fsvq->lock); + return; + } + args = req->args; copy_args_from_argbuf(args, req); @@ -788,6 +860,7 @@ static int virtio_fs_init_vq(struct virtio_fs *fs, struct virtio_fs_vq *fsvq, strncpy(fsvq->name, name, VQ_NAME_LEN); spin_lock_init(&fsvq->lock); INIT_LIST_HEAD(&fsvq->queued_reqs); + INIT_LIST_HEAD(&fsvq->wait_reqs); INIT_LIST_HEAD(&fsvq->end_reqs); INIT_LIST_HEAD(&fsvq->notify_reqs); init_completion(&fsvq->in_flight_zero); diff --git a/include/uapi/linux/fuse.h b/include/uapi/linux/fuse.h index 36ed092227fa..46838551ea84 100644 --- a/include/uapi/linux/fuse.h +++ b/include/uapi/linux/fuse.h @@ -184,6 +184,8 @@ * * 7.34 * - add FUSE_SYNCFS + * 7.35 + * - add FUSE_NOTIFY_LOCK */ #ifndef _LINUX_FUSE_H @@ -219,7 +221,7 @@ #define FUSE_KERNEL_VERSION 7 /** Minor version number of this interface */ -#define FUSE_KERNEL_MINOR_VERSION 34 +#define FUSE_KERNEL_MINOR_VERSION 35 /** The node ID of the root inode */ #define FUSE_ROOT_ID 1 @@ -529,6 +531,7 @@ enum fuse_notify_code { FUSE_NOTIFY_STORE = 4, FUSE_NOTIFY_RETRIEVE = 5, FUSE_NOTIFY_DELETE = 6, + FUSE_NOTIFY_LOCK = 7, FUSE_NOTIFY_CODE_MAX, }; @@ -920,6 +923,12 @@ struct fuse_notify_retrieve_in { uint64_t dummy4; }; +struct fuse_notify_lock_out { + uint64_t unique; + int32_t error; + int32_t padding; +}; + /* Device ioctls: */ #define FUSE_DEV_IOC_MAGIC 229 #define FUSE_DEV_IOC_CLONE _IOR(FUSE_DEV_IOC_MAGIC, 0, uint32_t) -- 2.31.1 _______________________________________________ Virtio-fs mailing list [email protected] https://listman.redhat.com/mailman/listinfo/virtio-fs
