Re: [PATCH 00/11] sockets: Attempt to drain the abstract socket swamp

[Markus Armbruster]

Daniel P. Berrangé <berrange@redhat.com> writes:

> On Fri, Oct 30, 2020 at 11:11:19AM +0100, Markus Armbruster wrote:
>> Marc-André Lureau <marcandre.lureau@gmail.com> writes:
>> 
>> > Hi Markus,
>> >
>> > On Thu, Oct 29, 2020 at 5:43 PM Markus Armbruster <armbru@redhat.com> 
>> > wrote:
>> >
>> >> In my opinion, the Linux-specific abstract UNIX domain socket feature
>> >> introduced in 5.1 should have been rejected.  The feature is niche,
>> >> the interface clumsy, the implementation buggy and incomplete, and the
>> >> test coverage insufficient.  Review fail.
>> >>
>> >
>> > I also failed (as chardev maintainer..) to not only review but weigh in and
>> > discuss the merits or motivations behind it.
>> >
>> > I agree with you. Also the commit lacks motivation behind this "feature".
>> >
>> >
>> >> Fixing the parts we can still fix now is regrettably expensive.  If I
>> >> had the power to decide, I'd unceremoniously revert the feature,
>> >> compatibility to 5.1 be damned.  But I don't, so here we go.
>> >>
>> >> I'm not sure this set of fixes is complete.  However, I already spent
>> >> too much time on this, so out it goes.  Lightly tested.
>> >>
>> >> Regardless, I *will* make time for ripping the feature out if we
>> >> decide to do that.  Quick & easy way to avoid reviewing this series
>> >> *hint* *hint*.
>> >>
>> >
>> > well, fwiw, I would also take that approach too, to the risk of upsetting
>> > the users.
>> 
>> Reverting the feature requires rough consensus and a patch.
>> 
>> I can provide a patch, but let's give everybody a chance to object
>> first.

Daniel, do you object, yes or no?

I need to know to avoid wasting even more time.

>> >            But maybe we can get a clear reason behind it before that
>> > happens. (sorry, I didn't dig the ML archive is such evidence is there, it
>> > should have been in the commit message too)
>> 
>> I just did, and found next to nothing.
>> 
>> This is the final cover letter:
>> 
>>     qemu-sockets: add abstract UNIX domain socket support
>> 
>>     qemu does not support abstract UNIX domain
>>     socket address. Add this ability to make qemu handy
>>     when abstract address is needed.
>> 
>> Boils down to "$feature is needed because it's handy when it's needed",
>> which is less than helpful.
>
> Well if you have an existing application that uses abstract sockets,
> and you want to connect QEMU to it, then QEMU needs to support it,
> or you are forced to interject a proxy between your app and QEMU
> which is an extra point of failure and lantency. I was interested
> in whether there was a specific application they were using, but
> that is largely just from a curiosity POV. There's enough usage of
> abstract sockets in apps in general that is it clearly a desirable
> feature to enable.
>
> Even if no external app is involved and you're just connecting
> together 2 QEMU processes' chardevs, abstract sockets are interesting
> because of their differing behaviour to non-abstract sockets.
>
> Most notably non-abstract sockets are tied to the filesystem mount
> namespace in Linux, where as abstract sockets are tied to the network
> namespace. This is a useful distinction in the container world. Ordinarily
> you can't connect QEMUs in 2 separate containers together, because they
> always have distinct mount namespaces. There is often the ability to
> share network namespaces between containers though, and thus unlock
> use of abstract sockets for communications. 

If this was patch review, I'd now ask the patch submitter to work it
into the commit message.

Thanks anyway :)

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