hacking - aio_sendfile()

[Scott Long]

On Jul 11, 2013, at 11:48 AM, Konstantin Belousov <kostikbel at gmail.com> wrote:

> On Thu, Jul 11, 2013 at 11:44:32AM -0700, Scott Long wrote:
>> 
>> On Jul 10, 2013, at 11:17 PM, Konstantin Belousov <kostikbel at gmail.com> wrote:
>> 
>>> On Wed, Jul 10, 2013 at 04:36:23PM -0700, Adrian Chadd wrote:
>>>> Hiya,
>>>> 
>>>> I've started writing an aio_sendfile() syscall.
>>>> 
>>>> http://people.freebsd.org/~adrian/ath/20130710-aio-sendfile-3.diff
>>>> 
>>>> Yes, the diff is against -HEAD and not stable/9.
>>>> 
>>>> It's totally horrible, hackish and likely bad. I've only done some
>>>> very, very basic testing to ensure it actually works; i haven't at all
>>>> stress tested it out yet. It's also very naive - I'm not at all doing
>>>> any checks to see whether I can short-cut to do the aio there and
>>>> then; I'm always queuing the sendfile() op through the worker threads.
>>>> That's likely stupid and inefficient in a lot of cases, but it at
>>>> least gets the syscall up and working.
>>> Yes, it is naive, but for different reason.
>>> 
>>> The kern_sendfile() is synchronous function, it only completes after
>>> the other end of the network communication allows it. This means
>>> that calling kern_sendfile() from the aio thread blocks the thread
>>> indefinitely by unbounded sleep.
>> 
>> 
>> No, kern_sendfile is async unless you specify the SF_SYNC hack flag.
>> Otherwise, it'll fill the socket buffer and then return immediately, unless
>> the socket buffer is full and the socket is set to blocking mode.  That's
>> outside the scope, as I said in my previous email.
> 
> You do not understand what I said, please re-read both my mail and code
> before replying.  Implementing aio_sendfile() as proposed would create
> yet another possibility of indefinitely block all processes using aio.

I'm lost, maybe I missed some emails?  I see a set of emails where you incorrectly
state that kern_sendfile() will always call sbwait(), and then you backtrack on that
and claim that it's unacceptable to enforce that SS_NBIO be used for aio operations.
I apologize if I'm missing something here.

Scott