Make piping to subprocesses more robust on MS-Windows

* src/w32.c (sys_write): Don't write to a pipe more stuff than its
buffer can hold.  Don't return -1 if something has been written to
the pipe.  Zero out 'errno' before calling '_write', to avoid
returning a stale value.  (Bug#22344)
* src/w32proc.c (syms_of_ntproc) <w32-pipe-buffer-size>: New variable.
* src/w32.c (pipe2): Use it to request a user-defined size for the
pipe being created.

* etc/NEWS: Mention 'w32-pipe-buffer-size'.

* doc/emacs/msdos.texi (Windows Processes): Document
'w32-pipe-buffer-size'.

1 files changed, 6 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index 85ec30ac033..10fcb7e3fd4 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -1762,6 +1762,12 @@ this has no effect.
 ** The new function 'w32-application-type' returns the type of an
 MS-Windows application given the name of its executable program file.
 
+** New variable `w32-pipe-buffer-size'.
+It can be used to tune the size of the buffer of pipes created for
+communicating with subprocesses, when the program run by a subprocess
+exhibits unusual buffering behavior.  Default is zero, which lets the
+OS use its default size.
+
 
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