linux-kernel - RE: [PATCH 4/6] Drivers: hv: vmbus: Introduce vmbus_request_addr

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Date:   Mon, 11 Apr 2022 02:31:59 +0000
From:   "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
To:     Andrea Parri <parri.andrea@...il.com>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Wei Hu <weh@...rosoft.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczynski <kw@...ux.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 4/6] Drivers: hv: vmbus: Introduce
 vmbus_request_addr_match()

From: Andrea Parri <parri.andrea@...il.com> Sent: Friday, April 8, 2022 1:38 PM
> 
> > > > In the case where a specific match is required, and trans_id is
> > > > valid but the addr's do not match, it looks like this function will
> > > > return the addr that didn't match, without removing the entry.
> > >
> > > Yes, that is consistent with the description on vmbus_request_addr_match():
> > >
> > >   Returns the memory address stored at @trans_id, or VMBUS_RQST_ERROR if
> > >   @trans_id is not contained in the requestor.
> > >
> > >
> > > > Shouldn't it return VMBUS_RQST_ERROR in that case?
> > >
> > > Can certainly be done, although I'm not sure to follow your concerns.  Can
> > > you elaborate?
> > >
> >
> > Having the function return "success" when it failed to match is unexpected
> > for me.  There's only one invocation where we care about matching
> > (in hv_compose_msi_msg).  In that invocation the purpose for matching is to
> > not remove the wrong entry, and the return value is ignored.  So I think
> > it all works correctly.
> 
> You're reading it wrongly: the point is that there's nothing wrong in *not
> removing the "wrong entry" (or in failing to match).  In the mentioned use,
> that means the channel callback has already processed "our" request, and
> that we don't have to worry about the ID.  (Otherwise, i.e. if we do match,
> the callback will eventually scream "Invalid transaction".)
> 
> 
> > Just thinking out loud, maybe vmbus_request_addr_match() should be
> > renamed to vmbus_request_addr_remove(), and not have a return value?
> 
> Mmh.  We have vmbus_request_addr() that (always) removes the ID; it seems
> a _remove() would just add to the confusion.  And removing the return value
> would mean duplicating most of vmbus_request_addr() in the "new" function.
> So, I'm not convinced that's the right thing to do.  I'm inclined to leave
> this patch as is (and, as usual, happy to be proven wrong).
> 

I'll defer to your judgment.  I don't see anything that broken with the
patch as written, so I can live with it as is.

Michael