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Re: [PATCH 1/1] mingw: optionally disable side-band-64k for transport




Hi brian,

On Mon, 29 Apr 2019, brian m. carlson wrote:

> On Mon, Apr 29, 2019 at 03:04:36PM -0700, Thomas Braun via GitGitGadget wrote:
> > From: Thomas Braun <thomas.braun@xxxxxxxxxxxxxxx>
> >
> > Since commit 0c499ea60f (send-pack: demultiplex a sideband stream with
> > status data, 2010-02-05) the built-in send-pack uses the side-band-64k
> > capability if advertised by the server.
> >
> > Unfortunately this breaks pushing over the dump git protocol if used
> > over a network connection when using MinGW (but *not* when using
> > mingw-w64).
> >
> > The detailed reasons for this, are courtesy of Jeff Preshing, quoted
> > from https://groups.google.com/d/msg/msysgit/at8D7J-h7mw/eaLujILGUWoJ:
> >
> > 	MinGW wraps Windows sockets in CRT file descriptors in order to
> > 	mimic the functionality of POSIX sockets. This causes msvcrt.dll
> > 	to treat sockets as Installable File System (IFS) handles,
> > 	calling ReadFile, WriteFile, DuplicateHandle and CloseHandle on
> > 	them. This approach works well in simple cases on recent
> > 	versions of Windows, but does not support all usage patterns.
> > 	In particular, using this approach, any attempt to read & write
> > 	concurrently on the same socket (from one or more processes)
> > 	will deadlock in a scenario where the read waits for a response
> > 	from the server which is only invoked after the write. This is
> > 	what send_pack currently attempts to do in the use_sideband
> > 	codepath.
>
> Since this is a platform-specific issue, can we address this using a
> compile-time constant instead of a config option? It would be better to
> do the right thing automatically in this case and not have to have
> people set a config option. It will also allow us to not to have to
> maintain a config option indefinitely if MinGW becomes more capable in
> the future.

I was really not sure at the time whether this would be fixed in MinGW at
some stage, and with the switch to mingw-w64 (by moving from MSys to MSYS2
as of Git for Windows 2.x) we do not really have any concrete need for it
anymore.

I just thought that it might benefit somebody (it was my impression that
Hannes Sixt still built his own copy with MSys/MinGW, and we do have a
track record of maintaining certain things even for single users, see e.g.
our insistence on creating the .git/branches/ directory upon `git init`).

But if the consensus is that we do not need this at all anymore, I'll be
just as happy to drop that patch.

Ciao,
Dscho