[Virtio-fs] [PATCH 1/4] virtiofsd: send reply correctly on read failure

[Dr. David Alan Gilbert]

* Liu Bo (bo.liu at linux.alibaba.com) wrote:
> From: Eryu Guan <eguan at linux.alibaba.com>
> 
> Currently when a lo_read() operation fails, we don't send the failure
> back to fuse client, and read(2) operation from guest kernel would hang
> on waiting for the reply.
> 
> This is easily triggered by a direct read with non-aligned length.
> 
> Fix it by detecting preadv(2) error in virtio_send_data_iov(), and
> teaching fuse_reply_data() to reply error on error case.

Thank you for spotting this.

> Reviewed-by: Liu Bo <bo.liu at linux.alibaba.com>
> Signed-off-by: Eryu Guan <eguan at linux.alibaba.com>
> ---
>  contrib/virtiofsd/fuse_lowlevel.c |  4 ++--
>  contrib/virtiofsd/fuse_virtio.c   | 12 +++++++++---
>  2 files changed, 11 insertions(+), 5 deletions(-)
> 
> diff --git a/contrib/virtiofsd/fuse_lowlevel.c b/contrib/virtiofsd/fuse_lowlevel.c
> index 111c6e1..aeb5fe2 100644
> --- a/contrib/virtiofsd/fuse_lowlevel.c
> +++ b/contrib/virtiofsd/fuse_lowlevel.c
> @@ -524,11 +524,11 @@ int fuse_reply_data(fuse_req_t req, struct fuse_bufvec *bufv,
>  	out.error = 0;
>  
>  	res = fuse_send_data_iov(req->se, req->ch, iov, 1, bufv, flags);
> -	if (res <= 0) {
> +	if (res >= 0) {

I need to go and ask the upstream fuse list about this; it's not clear
to me what fuse_send_data_iov is supposed to return;  let me clarify
that and get back to you.

Dave

>  		fuse_free_req(req);
>  		return res;
>  	} else {
> -		return fuse_reply_err(req, res);
> +		return fuse_reply_err(req, -res);
>  	}
>  }
>  
> diff --git a/contrib/virtiofsd/fuse_virtio.c b/contrib/virtiofsd/fuse_virtio.c
> index ca988aa..0b5736d 100644
> --- a/contrib/virtiofsd/fuse_virtio.c
> +++ b/contrib/virtiofsd/fuse_virtio.c
> @@ -333,8 +333,13 @@ int virtio_send_data_iov(struct fuse_session *se, struct fuse_chan *ch,
>                  ret = preadv(buf->buf[0].fd, in_sg_ptr, in_sg_cpy_count, buf->buf[0].pos);
>  
>                  if (se->debug)
> -                        fprintf(stderr, "%s: preadv_res=%d len=%zd\n",
> -                                __func__, ret, len);
> +                        fprintf(stderr, "%s: preadv_res=%d(%s) len=%zd\n",
> +                                __func__, ret, strerror(errno), len);
> +                if (ret == -1) {
> +                        ret = -errno;
> +                        free(in_sg_cpy);
> +                        goto err;
> +                }
>                  if (ret < len && ret) {
>                          if (se->debug)
>                                  fprintf(stderr, "%s: ret < len\n", __func__);
> @@ -379,7 +384,8 @@ int virtio_send_data_iov(struct fuse_session *se, struct fuse_chan *ch,
>          vu_queue_notify(&se->virtio_dev->dev, q);
>  
>  err:
> -        ch->qi->reply_sent = true;
> +        if (!ret)
> +                ch->qi->reply_sent = true;
>  
>          return ret;
>  }
> -- 
> 1.8.3.1
> 
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--
Dr. David Alan Gilbert / dgilbert at redhat.com / Manchester, UK