Re: [PATCH 09/25] errno: add POSIX error codes EMSGSIZE, ECONNREFUSED to the ABI

From: "Jan Beulich" <JBeulich@suse.com>
To: Christopher Clark <christopher.w.clark@gmail.com>
Cc: Tim Deegan <tim@xen.org>,
	Stefano Stabellini <sstabellini@kernel.org>,
	Wei Liu <wei.liu2@citrix.com>,
	ross.philipson@gmail.com, Jason Andryuk <jandryuk@gmail.com>,
	Daniel Smith <dpsmith@apertussolutions.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>,
	Ian Jackson <Ian.Jackson@eu.citrix.com>,
	Rich Persaud <persaur@gmail.com>,
	James McKenzie <voreekf@madingley.org>,
	George Dunlap <George.Dunlap@eu.citrix.com>,
	Julien Grall <julien.grall@arm.com>,
	Paul Durrant <paul.durrant@citrix.com>,
	xen-devel <xen-devel@lists.xenproject.org>,
	eric chanudet <eric.chanudet@gmail.com>
Subject: Re: [PATCH 09/25] errno: add POSIX error codes EMSGSIZE, ECONNREFUSED to the ABI
Date: Tue, 04 Dec 2018 03:04:01 -0700	[thread overview]
Message-ID: <5C065111020000780020297A@prv1-mh.provo.novell.com> (raw)
In-Reply-To: <CACMJ4Ga+x5=xRfyxpoXDgNz1zuB99xzr0_Y206PttDcAvtXBHA@mail.gmail.com>

>>> On 04.12.18 at 10:10, <christopher.w.clark@gmail.com> wrote:
> On Mon, Dec 3, 2018 at 7:42 AM Jan Beulich <JBeulich@suse.com> wrote:
>>
>> >>> On 01.12.18 at 02:32, <christopher.w.clark@gmail.com> wrote:
>> > http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/errno.h.html 
>> > describes these codes thus:
>> >     EMSGSIZE     : "Message too large"
>> >     ECONNREFUSED : "Connection refused".
>>
>> If you were to go solely by what POSIX mandates to have, more
>> additions would be necessary afaict. We had limited ourselves to
>> some basic set, so selective additions need further rationale put
>> here. The more that for both added error codes the use case in
>> the hypervisor isn't immediately obvious.
> 
> Thanks for reviewing the series and the previous iterations of this work.
> 
> I note your other message indicating a preference for including these
> changes at point of first use and I will do so in the next revision.

Actually, for the error code additions here I wouldn't insist on
them getting folded into patches using them, as long as it is
explained well here why the additions are desired.

> An aside before the rationales below: part of the motivation for
> selection of these error codes is to continue alignment with the
> modern v4v implementation in uxen where possible.
> 
> EMSGSIZE:
> 
> This series proposes to return EMSGSIZE for a sendv operation (patch
> #15) where an excess amount of data, across all iovs, has been
> supplied, exceeding either the statically configured maximum size of a
> transmittable message, or the (variable) size of the ring registered
> by another domain.

Ah yes, for a send-like operation I can see its use.

> ECONNREFUSED:
> 
> This series proposes to return ECONNREFUSED whenever a remote domain
> is specified that either does not exist or is not argo-enabled.
> This affects both the ring registration and sending data operations.
> (register op, patch #13; sendv op, patch #15)
> 
> ECONNREFUSED seems plausible for this use as it is determined by the
> remote domain state within the hypervisor.

Makes sense for the not argo-enabled case. The domain not
existing case, however, is nothing argo-specific, and we use a
pretty consistent -ESRCH in such cases, I think.

Jan

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