Re: [Virtio-fs] [PATCH 4/4] virtiofsd: Implement blocking posix locks

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Vivek Goyal (vgoyal@redhat.com) wrote:
> As of now we don't support fcntl(F_SETLKW) and if we see one, we return
> -EOPNOTSUPP.
> 
> Change that by accepting these requests and returning a reply immediately
> asking caller to wait. Once lock is available, send a notification to
> the waiter indicating lock is available.
> 
> Signed-off-by: Vivek Goyal <vgoyal@redhat.com>
> ---
>  contrib/virtiofsd/fuse_kernel.h    |  7 +++
>  contrib/virtiofsd/fuse_lowlevel.c  | 23 +++++++-
>  contrib/virtiofsd/fuse_lowlevel.h  | 25 ++++++++
>  contrib/virtiofsd/fuse_virtio.c    | 94 ++++++++++++++++++++++++++++--
>  contrib/virtiofsd/passthrough_ll.c | 49 +++++++++++++---
>  5 files changed, 182 insertions(+), 16 deletions(-)
> 
> diff --git a/contrib/virtiofsd/fuse_kernel.h b/contrib/virtiofsd/fuse_kernel.h
> index 2bdc8b1c88..d4d65c5414 100644
> --- a/contrib/virtiofsd/fuse_kernel.h
> +++ b/contrib/virtiofsd/fuse_kernel.h
> @@ -444,6 +444,7 @@ enum fuse_notify_code {
>  	FUSE_NOTIFY_STORE = 4,
>  	FUSE_NOTIFY_RETRIEVE = 5,
>  	FUSE_NOTIFY_DELETE = 6,
> +	FUSE_NOTIFY_LOCK = 7,
>  	FUSE_NOTIFY_CODE_MAX,
>  };
>  
> @@ -836,6 +837,12 @@ struct fuse_notify_retrieve_in {
>  	uint64_t	dummy4;
>  };
>  
> +struct fuse_notify_lock_out {
> +	uint64_t	id;
> +	int32_t		error;
> +	int32_t		padding;
> +};
> +
>  /* Device ioctls: */
>  #define FUSE_DEV_IOC_CLONE	_IOR(229, 0, uint32_t)
>  
> diff --git a/contrib/virtiofsd/fuse_lowlevel.c b/contrib/virtiofsd/fuse_lowlevel.c
> index d4a42d9804..f706e440bf 100644
> --- a/contrib/virtiofsd/fuse_lowlevel.c
> +++ b/contrib/virtiofsd/fuse_lowlevel.c
> @@ -183,7 +183,8 @@ int fuse_send_reply_iov_nofree(fuse_req_t req, int error, struct iovec *iov,
>  {
>  	struct fuse_out_header out;
>  
> -	if (error <= -1000 || error > 0) {
> +	/* error = 1 has been used to signal client to wait for notificaiton */
> +	if (error <= -1000 || error > 1) {
>  		fuse_log(FUSE_LOG_ERR, "fuse: bad error value: %i\n",	error);
>  		error = -ERANGE;
>  	}
> @@ -291,6 +292,12 @@ int fuse_reply_err(fuse_req_t req, int err)
>  	return send_reply(req, -err, NULL, 0);
>  }
>  
> +int fuse_reply_wait(fuse_req_t req)
> +{
> +	/* TODO: This is a hack. Fix it */
> +	return send_reply(req, 1, NULL, 0);
> +}
> +
>  void fuse_reply_none(fuse_req_t req)
>  {
>  	fuse_free_req(req);
> @@ -2207,6 +2214,20 @@ static int send_notify_iov(struct fuse_session *se, int notify_code,
>  	return fuse_send_msg(se, NULL, iov, count);
>  }
>  
> +int fuse_lowlevel_notify_lock(struct fuse_session *se, uint64_t req_id,
> +			      int32_t error)
> +{
> +	struct fuse_notify_lock_out outarg;
> +	struct iovec iov[2];
> +
> +	outarg.id = req_id;
> +	outarg.error = -error;
> +
> +	iov[1].iov_base = &outarg;
> +	iov[1].iov_len = sizeof(outarg);
> +	return send_notify_iov(se, FUSE_NOTIFY_LOCK, iov, 2);
> +}
> +
>  int fuse_lowlevel_notify_poll(struct fuse_pollhandle *ph)
>  {
>  	if (ph != NULL) {
> diff --git a/contrib/virtiofsd/fuse_lowlevel.h b/contrib/virtiofsd/fuse_lowlevel.h
> index e664d2d12d..f0a94683b5 100644
> --- a/contrib/virtiofsd/fuse_lowlevel.h
> +++ b/contrib/virtiofsd/fuse_lowlevel.h
> @@ -1251,6 +1251,22 @@ struct fuse_lowlevel_ops {
>   */
>  int fuse_reply_err(fuse_req_t req, int err);
>  
> +/**
> + * Ask caller to wait for lock.
> + *
> + * Possible requests:
> + *   setlkw
> + *
> + * If caller sends a blocking lock request (setlkw), then reply to caller
> + * that wait for lock to be available. Once lock is available caller will
> + * receive a notification with request's unique id. Notification will
> + * carry info whether lock was successfully obtained or not.
> + *
> + * @param req request handle
> + * @return zero for success, -errno for failure to send reply
> + */
> +int fuse_reply_wait(fuse_req_t req);
> +
>  /**
>   * Don't send reply
>   *
> @@ -1704,6 +1720,15 @@ int fuse_lowlevel_notify_delete(struct fuse_session *se,
>  int fuse_lowlevel_notify_store(struct fuse_session *se, fuse_ino_t ino,
>  			       off_t offset, struct fuse_bufvec *bufv,
>  			       enum fuse_buf_copy_flags flags);
> +/**
> + * Notify event related to previous lock request
> + *
> + * @param se the session object
> + * @param req_id the id of the request which requested setlkw
> + * @param error zero for success, -errno for the failure
> + */
> +int fuse_lowlevel_notify_lock(struct fuse_session *se, uint64_t req_id,
> +			      int32_t error);
>  
>  /* ----------------------------------------------------------- *
>   * Utility functions					       *
> diff --git a/contrib/virtiofsd/fuse_virtio.c b/contrib/virtiofsd/fuse_virtio.c
> index 982b6ad0bd..98d27e7642 100644
> --- a/contrib/virtiofsd/fuse_virtio.c
> +++ b/contrib/virtiofsd/fuse_virtio.c
> @@ -215,6 +215,81 @@ static void copy_iov(struct iovec *src_iov, int src_count,
>      }
>  }
>  
> +static int virtio_send_notify_msg(struct fuse_session *se, struct iovec *iov,
> +				  int count)
> +{
> +    struct fv_QueueInfo *qi;
> +    VuDev *dev = &se->virtio_dev->dev;
> +    VuVirtq *q;
> +    FVRequest *req;
> +    VuVirtqElement *elem;
> +    unsigned int in_num, bad_in_num = 0, bad_out_num = 0;
> +    struct fuse_out_header *out = iov[0].iov_base;
> +    size_t in_len, tosend_len = iov_size(iov, count);
> +    struct iovec *in_sg;
> +    int ret = 0;
> +
> +    /* Notifications have unique == 0 */
> +    assert (!out->unique);
> +
> +    if (!se->notify_enabled)
> +        return -EOPNOTSUPP;
> +
> +    /* If notifications are enabled, queue index 1 is notification queue */
> +    qi = se->virtio_dev->qi[1];
> +    q = vu_get_queue(dev, qi->qidx);
> +
> +    pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> +    pthread_mutex_lock(&qi->vq_lock);
> +    /* Pop an element from queue */
> +    req = vu_queue_pop(dev, q, sizeof(FVRequest), &bad_in_num, &bad_out_num);

You don't need bad_in_num/bad_out_num - just pass NULL for both; they're
only needed if you expect to read/write data that's not mappable (i.e.
in our direct write case).

> +    if (!req) {
> +        /* TODO: Implement some sort of ring buffer and queue notifications
> +	 * on that and send these later when notification queue has space
> +	 * available.
> +	 */
> +        return -ENOSPC;
> +    }
> +    pthread_mutex_unlock(&qi->vq_lock);
> +    pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> +
> +    out->len = tosend_len;
> +    elem = &req->elem;
> +    in_num = elem->in_num;
> +    in_sg = elem->in_sg;
> +    in_len = iov_size(in_sg, in_num);
> +    fuse_log(FUSE_LOG_DEBUG, "%s: elem %d: with %d in desc of length %zd\n",
> +             __func__, elem->index, in_num,  in_len);
> +
> +    if (in_len < sizeof(struct fuse_out_header)) {
> +        fuse_log(FUSE_LOG_ERR, "%s: elem %d too short for out_header\n",
> +                 __func__, elem->index);
> +        ret = -E2BIG;
> +        goto out;
> +    }
> +
> +    if (in_len < tosend_len) {
> +        fuse_log(FUSE_LOG_ERR, "%s: elem %d too small for data len"
> +                 " %zd\n", __func__, elem->index, tosend_len);
> +        ret = -E2BIG;
> +        goto out;
> +    }
> +
> +    /* First copy the header data from iov->in_sg */
> +    copy_iov(iov, count, in_sg, in_num, tosend_len);
> +
> +    /* TODO: Add bad_innum handling */
> +    pthread_rwlock_rdlock(&qi->virtio_dev->vu_dispatch_rwlock);
> +    pthread_mutex_lock(&qi->vq_lock);
> +    vu_queue_push(dev, q, elem, tosend_len);
> +    vu_queue_notify(dev, q);
> +    pthread_mutex_unlock(&qi->vq_lock);
> +    pthread_rwlock_unlock(&qi->virtio_dev->vu_dispatch_rwlock);
> +out:
> +    free(req);
> +    return ret;
> +}
> +
>  /*
>   * Called back by ll whenever it wants to send a reply/message back
>   * The 1st element of the iov starts with the fuse_out_header
> @@ -223,11 +298,11 @@ static void copy_iov(struct iovec *src_iov, int src_count,
>  int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,
>                      struct iovec *iov, int count)
>  {
> -    FVRequest *req = container_of(ch, FVRequest, ch);
> -    struct fv_QueueInfo *qi = ch->qi;
> +    FVRequest *req;
> +    struct fv_QueueInfo *qi;
>      VuDev *dev = &se->virtio_dev->dev;
> -    VuVirtq *q = vu_get_queue(dev, qi->qidx);
> -    VuVirtqElement *elem = &req->elem;
> +    VuVirtq *q;
> +    VuVirtqElement *elem;
>      int ret = 0;
>  
>      assert(count >= 1);
> @@ -238,8 +313,15 @@ int virtio_send_msg(struct fuse_session *se, struct fuse_chan *ch,
>  
>      size_t tosend_len = iov_size(iov, count);
>  
> -    /* unique == 0 is notification, which we don't support */
> -    assert(out->unique);
> +    /* unique == 0 is notification */
> +    if (!out->unique)
> +        return virtio_send_notify_msg(se, iov, count);
> +
> +    assert(ch);
> +    req = container_of(ch, FVRequest, ch);
> +    elem = &req->elem;
> +    qi = ch->qi;
> +    q = vu_get_queue(dev, qi->qidx);
>      assert(!req->reply_sent);
>  
>      /* The 'in' part of the elem is to qemu */
> diff --git a/contrib/virtiofsd/passthrough_ll.c b/contrib/virtiofsd/passthrough_ll.c
> index 028e7da273..ed52953565 100644
> --- a/contrib/virtiofsd/passthrough_ll.c
> +++ b/contrib/virtiofsd/passthrough_ll.c
> @@ -1925,7 +1925,10 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino,
>  	struct lo_data *lo = lo_data(req);
>  	struct lo_inode *inode;
>  	struct lo_inode_plock *plock;
> -	int ret, saverr = 0;
> +	int ret, saverr = 0, ofd;
> +	uint64_t unique;
> +	struct fuse_session *se = req->se;
> +	bool async_lock = false;
>  
>  	fuse_log(FUSE_LOG_DEBUG, "lo_setlk(ino=%" PRIu64 ", flags=%d)"
>  		 " cmd=%d pid=%d owner=0x%lx sleep=%d l_whence=%d"
> @@ -1933,11 +1936,6 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino,
>  		 lock->l_type, lock->l_pid, fi->lock_owner, sleep,
>  		 lock->l_whence, lock->l_start, lock->l_len);
>  
> -	if (sleep) {
> -		fuse_reply_err(req, EOPNOTSUPP);
> -		return;
> -	}
> -
>  	inode = lo_inode(req, ino);
>  	if (!inode) {
>  		fuse_reply_err(req, EBADF);
> @@ -1950,21 +1948,54 @@ static void lo_setlk(fuse_req_t req, fuse_ino_t ino,
>  
>  	if (!plock) {
>  		saverr = ret;
> +		pthread_mutex_unlock(&inode->plock_mutex);
>  		goto out;
>  	}
>  
> +	/*
> +	 * plock is now released when inode is going away. We already have
> +	 * a reference on inode, so it is guaranteed that plock->fd is
> +	 * still around even after dropping inode->plock_mutex lock
> +	 */
> +	ofd = plock->fd;
> +	pthread_mutex_unlock(&inode->plock_mutex);
> +
> +	/*
> +	 * If this lock request can block, request caller to wait for
> +	 * notification. Do not access req after this. Once lock is
> +	 * available, send a notification instead.
> +	 */
> +	if (sleep && lock->l_type != F_UNLCK) {
> +		/*
> +		 * If notification queue is not enabled, can't support async
> +		 * locks.
> +		 */
> +		if (!se->notify_enabled) {
> +			saverr = EOPNOTSUPP;
> +			goto out;
> +		}
> +		async_lock = true;
> +		unique = req->unique;
> +		fuse_reply_wait(req);
> +	}
>  	/* TODO: Is it alright to modify flock? */
>  	lock->l_pid = 0;
> -	ret = fcntl(plock->fd, F_OFD_SETLK, lock);
> +	if (async_lock)
> +		ret = fcntl(ofd, F_OFD_SETLKW, lock);
> +	else
> +		ret = fcntl(ofd, F_OFD_SETLK, lock);

What happens if the guest is rebooted after it's asked
for, but not been granted a lock?

Dave

>  	if (ret == -1) {
>  		saverr = errno;
>  	}
>  
>  out:
> -	pthread_mutex_unlock(&inode->plock_mutex);
>  	lo_inode_put(lo, &inode);
>  
> -	fuse_reply_err(req, saverr);
> +	if (!async_lock)
> +		fuse_reply_err(req, saverr);
> +	else {
> +		fuse_lowlevel_notify_lock(se, unique, saverr);
> +	}
>  }
>  
>  static void lo_fsyncdir(fuse_req_t req, fuse_ino_t ino, int datasync,
> -- 
> 2.20.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK