linux-kernel - Re: [patch v8 3/7] nbd: check sock index in nbd_read

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Message-ID: <YUtSJ/bfKZ9QJUaY@pc181009.grep.be>
Date:   Wed, 22 Sep 2021 17:56:23 +0200
From:   Wouter Verhelst <w@...r.be>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     "yukuai (C)" <yukuai3@...wei.com>, josef@...icpanda.com,
        axboe@...nel.dk, hch@...radead.org, linux-block@...r.kernel.org,
        nbd@...er.debian.org, linux-kernel@...r.kernel.org,
        yi.zhang@...wei.com
Subject: Re: [patch v8 3/7] nbd: check sock index in nbd_read_stat()

On Wed, Sep 22, 2021 at 05:22:07PM +0800, Ming Lei wrote:
> On Sun, Sep 19, 2021 at 06:34:28PM +0800, yukuai (C) wrote:
> > On 2021/09/16 17:33, Yu Kuai wrote:
> > > The sock that clent send request in nbd_send_cmd() and receive reply
> > > in nbd_read_stat() should be the same.
> > > 
> > > Signed-off-by: Yu Kuai <yukuai3@...wei.com>
> > > ---
> > >   drivers/block/nbd.c | 4 ++++
> > >   1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/drivers/block/nbd.c b/drivers/block/nbd.c
> > > index 614c6ab2b8fe..c724a5bd7fa4 100644
> > > --- a/drivers/block/nbd.c
> > > +++ b/drivers/block/nbd.c
> > > @@ -746,6 +746,10 @@ static struct nbd_cmd *nbd_read_stat(struct nbd_device *nbd, int index)
> > >   		ret = -ENOENT;
> > >   		goto out;
> > >   	}
> > > +	if (cmd->index != index) {
> > > +		dev_err(disk_to_dev(nbd->disk), "Unexpected reply %d from different sock %d (expected %d)",
> > > +			tag, index, cmd->index);
> > > +	}
> > >   	if (cmd->cmd_cookie != nbd_handle_to_cookie(handle)) {
> > >   		dev_err(disk_to_dev(nbd->disk), "Double reply on req %p, cmd_cookie %u, handle cookie %u\n",
> > >   			req, cmd->cmd_cookie, nbd_handle_to_cookie(handle));
> > > 
> > 
> > Hi, Ming
> > 
> > Any suggestions about this patch?
> 
> I think this one relies on nbd protocol between server and client, and
> does the protocol require both request and reply xmitted via same
> socket?

As Eric already answered: yes, the request and reply are specified such
that they must be transmitted over the same socket.

For more details, you can find the protocol specification at
https://github.com/NetworkBlockDevice/nbd/blob/master/doc/proto.md

Please note that the protocol defined there has some options that are
not currently supported by the Linux nbd implementation -- specifically
the "structured reply" message format (and all that requires it) is not
implemented (yet?).

-- 
     w@...r.{be,co.za}
wouter@...ep.be,fosdem.org,debian.org}