linux-kernel - Re: [Xen-devel] [PATCH v4 07/18] xen/pvcalls: implement socket command

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Message-ID: <alpine.DEB.2.10.1706221137460.12819@sstabellini-ThinkPad-X260>
Date:   Thu, 22 Jun 2017 11:38:23 -0700 (PDT)
From:   Stefano Stabellini <sstabellini@...nel.org>
To:     Andrew Cooper <andrew.cooper3@...rix.com>
cc:     Stefano Stabellini <sstabellini@...nel.org>,
        Roger Pau Monné <roger.pau@...rix.com>,
        jgross@...e.com, linux-kernel@...r.kernel.org,
        xen-devel@...ts.xen.org, Stefano Stabellini <stefano@...reto.com>,
        boris.ostrovsky@...cle.com
Subject: Re: [Xen-devel] [PATCH v4 07/18] xen/pvcalls: implement socket
 command

On Thu, 22 Jun 2017, Andrew Cooper wrote:
> On 22/06/17 19:29, Stefano Stabellini wrote:
> > On Thu, 22 Jun 2017, Roger Pau Monné wrote:
> >> On Wed, Jun 21, 2017 at 01:16:56PM -0700, Stefano Stabellini wrote:
> >>> On Tue, 20 Jun 2017, Roger Pau Monné wrote:
> >>>> On Thu, Jun 15, 2017 at 12:09:36PM -0700, Stefano Stabellini wrote:
> >>>>> Just reply with success to the other end for now. Delay the allocation
> >>>>> of the actual socket to bind and/or connect.
> >>>>>
> >>>>> Signed-off-by: Stefano Stabellini <stefano@...reto.com>
> >>>>> CC: boris.ostrovsky@...cle.com
> >>>>> CC: jgross@...e.com
> >>>>> ---
> >>>>>  drivers/xen/pvcalls-back.c | 27 +++++++++++++++++++++++++++
> >>>>>  1 file changed, 27 insertions(+)
> >>>>>
> >>>>> diff --git a/drivers/xen/pvcalls-back.c b/drivers/xen/pvcalls-back.c
> >>>>> index 437c2ad..953458b 100644
> >>>>> --- a/drivers/xen/pvcalls-back.c
> >>>>> +++ b/drivers/xen/pvcalls-back.c
> >>>>> @@ -12,12 +12,17 @@
> >>>>>   * GNU General Public License for more details.
> >>>>>   */
> >>>>>  
> >>>>> +#include <linux/inet.h>
> >>>>>  #include <linux/kthread.h>
> >>>>>  #include <linux/list.h>
> >>>>>  #include <linux/radix-tree.h>
> >>>>>  #include <linux/module.h>
> >>>>>  #include <linux/semaphore.h>
> >>>>>  #include <linux/wait.h>
> >>>>> +#include <net/sock.h>
> >>>>> +#include <net/inet_common.h>
> >>>>> +#include <net/inet_connection_sock.h>
> >>>>> +#include <net/request_sock.h>
> >>>>>  
> >>>>>  #include <xen/events.h>
> >>>>>  #include <xen/grant_table.h>
> >>>>> @@ -54,6 +59,28 @@ struct pvcalls_fedata {
> >>>>>  static int pvcalls_back_socket(struct xenbus_device *dev,
> >>>>>  		struct xen_pvcalls_request *req)
> >>>>>  {
> >>>>> +	struct pvcalls_fedata *fedata;
> >>>>> +	int ret;
> >>>>> +	struct xen_pvcalls_response *rsp;
> >>>>> +
> >>>>> +	fedata = dev_get_drvdata(&dev->dev);
> >>>>> +
> >>>>> +	if (req->u.socket.domain != AF_INET ||
> >>>>> +	    req->u.socket.type != SOCK_STREAM ||
> >>>>> +	    (req->u.socket.protocol != IPPROTO_IP &&
> >>>>> +	     req->u.socket.protocol != AF_INET))
> >>>>> +		ret = -EAFNOSUPPORT;
> >>>> Sorry for jumping into this out of the blue, but shouldn't all the
> >>>> constants used above be part of the protocol? AF_INET/SOCK_STREAM/...
> >>>> are all part of POSIX, but their specific value is not defined in the
> >>>> standard, hence we should have XEN_AF_INET/XEN_SOCK_STREAM/... Or am I
> >>>> just missing something?
> >>> The values of these constants for the pvcalls protocol are defined by
> >>> docs/misc/pvcalls.markdown under "Socket families and address format".
> >>>
> >>> They happen to be the same as the ones defined by Linux as AF_INET,
> >>> SOCK_STREAM, etc, so in Linux I am just using those, but that is just an
> >>> implementation detail internal to the Linux kernel driver. What is
> >>> important from the protocol ABI perspective are the values defined by
> >>> docs/misc/pvcalls.markdown.
> >> Oh I see. I still think this should be part of the public pvcalls.h
> >> header, and that the error codes should be the ones defined in
> >> public/errno.h (or else also added to the pvcalls header).
> > This was done differently in the past, but now that we have a formal
> > process, a person in charge of new PV drivers reviews, and design
> > documents with clearly spelled out ABIs, I consider the design docs
> > under docs/misc as the official specification. We don't need headers
> > anymore, they are redundant. In fact, we cannot have two specifications,
> > and the design docs are certainly the official ones (we don't want the
> > specs to be written as header files in C). To me, the headers under
> > xen/include/public/io/ are optional helpers. It doesn't matter what's in
> > there, or if frontends and backends use them or not.
> >
> > There is really an argument for removing those headers, because they
> > might get out of sync with the spec by mistake, and in those cases, then
> > we really end up with two specifications for the same protocol. I would
> > be in favor of `git rm'ing all files under xen/include/public/io/ for
> > which we have a complete design doc under docs/misc.
> 
> +1.
> 
> Specifications should not be written in C.  The mess that is the net and
> block protocol ABIs are perfect examples of why.
> 
> Its fine (and indeed recommended) to provide a header file which
> describes the specified protocol, but the authoritative spec should be
> in text from.
> 
> I would really prefer if more people started using ../docs/specs/.  The
> migration v2 documents are currently lonely there...

I didn't realize we had a docs/specs. Feel free to move pvcalls and 9pfs
under there.