Re: Implementing aio_* and lio_* (async i/o) on Cygwin

[Corinna Vinschen <corinna-cygwin at cygwin dot com>]

On Mar 19 22:53, Mark Geisert wrote:
> Corinna Vinschen wrote (a while back):
> > However, using async IO, the only change necessary would be to change
> > prw_open to open an async handle, and pread/pwrite to wait for the
> > result if the current I/O is NOT async.  It may be necessary to add a
> > parameter or two to the pread/pwrite fhandler methods, but all the rest
> > of the functionality could be in the callers.
> 
> I see what you're suggesting; seems sly in a nice way :).
> 
> A small part I'm missing is in interfacing to the layer above this.  Are the
> aio_* functions supposed to be implemented as "real" syscalls (in
> syscalls.cc)? Or should they be implemented in their own aio.cc (which is
> where I have them ATM) and call pread()/pwrite() to do their dirty work?
> I'm unsure how "central" a syscall has to be to merit syscalls.cc location.

syscalls.cc is historical.  Cygwin has grown over a single file to keep
"syscalls" anyway, so having the interfaces in an aio.cc file doesn't
hurt.

> Regardless of which file the code is in, I was thinking I should copy
> syscalls.cc's pread() contents into aio_read(), for example, to start with.
> Then add extra param(s) as needed to the fhandler method call as you
> suggested.

That's definitely ok.  When I was talking about pread/pwrite in our
preliminary discussion on cygwin-patches, I was always talking about the
fhandler_disk_file::pread and fhandler_disk_file::pwrite methods in
fact, not the syscalls of the same name.  I'm sorry I was unclear there :}

> The problem with having aio_read() call pread() directly is how to tell
> pread() we want an async read.  That's why I was suggesting O_ASYNC
> previously, though I now understand that's the wrong direction to go.  What
> is the correct direction?

Looks like you're on the right track, just go ahead.  We can fix the
finer details later.


Thanks,
Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
Red Hat

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