From mboxrd@z Thu Jan 1 00:00:00 1970 Date: Thu, 18 Apr 2019 13:25:27 +0100 From: "Dr. David Alan Gilbert" Message-ID: <20190418122526.GE2984@work-vm> References: <20190416190858.16833-1-bo.liu@linux.alibaba.com> <20190416190858.16833-2-bo.liu@linux.alibaba.com> <20190417172621.GJ2839@work-vm> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190417172621.GJ2839@work-vm> Subject: Re: [Virtio-fs] [PATCH 1/4] virtiofsd: send reply correctly on read failure List-Id: Development discussions about virtio-fs List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Liu Bo , eguan@linux.alibaba.com Cc: virtio-fs@redhat.com * Dr. David Alan Gilbert (dgilbert@redhat.com) wrote: > * Liu Bo (bo.liu@linux.alibaba.com) wrote: > > From: Eryu Guan > > > > 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 > > Signed-off-by: Eryu Guan > > --- > > 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. Miklos replied to me on the upstream fuse list: https://sourceforge.net/p/fuse/mailman/fuse-devel/thread/CAOssrKdVViWewmh3nrfKkq6eaWNJ629AR7w90KG3XT2hV9_D1w%40mail.gmail.com/#msg36642807 so this comparison is actually already correct because a negative value means that something is wrong with the fuse connection (or in our case virtio) so we can't send an error reply anyway. > 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; So this will need to be ret = errno to give a postive error response to mean that the error was on the file side on the fuse side. (There's also another case below that where I set ret = EIO where it should be EIO I think) > > + 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; Yes, I think that's OK. Dave > > > > return ret; > > } > > -- > > 1.8.3.1 > > > > _______________________________________________ > > Virtio-fs mailing list > > Virtio-fs@redhat.com > > https://www.redhat.com/mailman/listinfo/virtio-fs > -- > Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK > > _______________________________________________ > Virtio-fs mailing list > Virtio-fs@redhat.com > https://www.redhat.com/mailman/listinfo/virtio-fs -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK