Re: [dpdk-dev] [PATCH v5 4/8] eal: sys/queue.h implementation for windows

[Jeff Shaw <jeffrey.b.shaw@intel.com>]

On Wed, Mar 27, 2019 at 12:00:49AM +0100, Thomas Monjalon wrote:
> 26/03/2019 23:34, Jeff Shaw:
> > On Tue, Mar 26, 2019 at 11:23:50PM +0100, Thomas Monjalon wrote:
> > > 26/03/2019 22:54, Jeff Shaw:
> > > > On Tue, Mar 26, 2019 at 10:47:54PM +0100, Thomas Monjalon wrote:
> > > > > 26/03/2019 22:14, Jeff Shaw:
> > > > > > On Tue, Mar 26, 2019 at 09:52:57PM +0100, Thomas Monjalon wrote:
> > > > > > > Even better would be to get it as a dependency outside of DPDK.
> > > > > > > Where this code come from?
> > > > > > > How other projects on Windows get it?
> > > > > > 
> > > > > > It comes from FreeBSD 12.0, specifically
> > > > > >   https://github.com/freebsd/freebsd/blob/releng/12.0/sys/sys/queue.h
> > > > > > 
> > > > > > It has been modified such that only the parts used by DPDK (i.e. TAILQ) are
> > > > > > implemented. The other stuff has been deleted. Windows does not have sys/queue.h,
> > > > > > so we reproduce it here.
> > > > > > 
> > > > > > Would it better to have this as a dependency outside of DPDK? I think pulling a file
> > > > > > from the internet and applying a patch (where we'd have to maintain a patch file
> > > > > > inside of DPDK's repo anyway) would be overkill when we just need a few lines of
> > > > > > code that will change very infrequently.
> > > > > 
> > > > > We already try to get the libbsd dependency on Linux.
> > > > > Why not mandate libbsd for Windows?
> > > > > It has this header file and a lot more:
> > > > > 	https://gitlab.freedesktop.org/libbsd/libbsd/blob/master/include/bsd/sys/queue.h
> > > > > 
> > > > > Relying on libbsd may avoid copying other files for Windows port.
> > > > 
> > > > I like that idea, though it doesn't look like libbsd builds on Windows, do you
> > > > know of a Windows version or one that doesn't depend on autotools to build?
> > > 
> > > It seems libbsd is not packaged for Windows.
> > > May be worth to ask opinions to libbsd maintainers.
> > > 
> > > Please could you list which other headers are required for the Windows port?
> > 
> > For helloworld the only one is sys/queue.h.
> > 
> > The dpdk-draft-windows repo has at least these (non-empty) ones:
> >   dirent.h
> >   getopt.h
> >   net/ethernet.h
> >   net/socket.h
> >   netinet/in.h
> >   netinet/tcp.h
> >   pthread.h
> >   rand48.h
> >   sched.h
> >   sys/_iovec.h
> >   sys/_sockaddr_storage.h
> >   sys/_termios.h
> >   sys/_types.h
> >   sys/cdefs.h
> >   sys/mman.h
> >   sys/netbsd/queue.h
> >   sys/queue.h
> >   sys/sysctl.h
> >   syslog.h
> >   termios.h
> >   unistd.h
> > 
> > There will likely be more as more libraries are identified with dependencies on UNIX-like
> > headers.
> 
> I would like we find a good solution for these headers.

I agree. I think the EAL is supposed to do this, however the current implementation generally
assums a UNIX OS under the EAL. The libbsd might be a possiblity.

> How other cross-platform projects are getting such dependencies?

One example is Python. I just briefly reviewed the code and they go through great lengths to
abstract the OS and implement custom, OS independent layers wherever required (e.g. sockets,
getopt). See Modules/posixmodule.c for a 14K LOC example.

Another example is Nginx. The underlying OS is always abstracted with disparate implementations
for, e.g. unix & windows. See src/os/unix and src/os/win32. An example is the "socket()" call
on unix, nginx "core" would call "ngx_socket()" which is a macro that is defined to use
"WSASocketW" on windows, and "socket" on unix.

> Is Cygwin a solution?

I think the goal is to be a native Windows application.