linux-kernel - Re: [PATCH v3 4/7] xen/9pfs: connect to the backend

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Date:   Wed, 15 Mar 2017 06:08:46 +0100
From:   Juergen Gross <jgross@...e.com>
To:     Stefano Stabellini <sstabellini@...nel.org>
Cc:     xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
        boris.ostrovsky@...cle.com,
        Stefano Stabellini <stefano@...reto.com>,
        Eric Van Hensbergen <ericvh@...il.com>,
        Ron Minnich <rminnich@...dia.gov>,
        Latchesar Ionkov <lucho@...kov.net>,
        v9fs-developer@...ts.sourceforge.net
Subject: Re: [PATCH v3 4/7] xen/9pfs: connect to the backend

On 14/03/17 22:22, Stefano Stabellini wrote:
> Hi Juergen,
> 
> thank you for the review!
> 
> On Tue, 14 Mar 2017, Juergen Gross wrote:
>> On 14/03/17 00:50, Stefano Stabellini wrote:
>>> Implement functions to handle the xenbus handshake. Upon connection,
>>> allocate the rings according to the protocol specification.
>>>
>>> Initialize a work_struct and a wait_queue. The work_struct will be used
>>> to schedule work upon receiving an event channel notification from the
>>> backend. The wait_queue will be used to wait when the ring is full and
>>> we need to send a new request.
>>>
>>> Signed-off-by: Stefano Stabellini <stefano@...reto.com>
>>> CC: boris.ostrovsky@...cle.com
>>> CC: jgross@...e.com
>>> CC: Eric Van Hensbergen <ericvh@...il.com>
>>> CC: Ron Minnich <rminnich@...dia.gov>
>>> CC: Latchesar Ionkov <lucho@...kov.net>
>>> CC: v9fs-developer@...ts.sourceforge.net
>>> ---

>> Did you think about using request_threaded_irq() instead of a workqueue?
>> For an example see e.g. drivers/scsi/xen-scsifront.c
> 
> I like workqueues :-)  It might come down to personal preferences, but I
> think workqueues are more flexible and a better fit for this use case.
> Not only it is easy to schedule work in a workqueue from the interrupt
> handler, but also they can be used for sleeping in the request function
> if there is not enough room on the ring. Besides, they can easily be
> configured to share a single thread or to have multiple independent
> threads.

I'm fine with the workqueues as long as you have decided to use them
considering the alternatives. :-)

>> Can't you use xenbus_read_unsigned() instead of xenbus_read()?
> 
> I can use xenbus_read_unsigned in the other cases below, but not here,
> because versions is in the form: "1,3,4"

Is this documented somewhere?

Hmm, are any of the Xenstore entries documented? Shouldn't this be done
in xen_9pfs.h ?


Juergen