From 34980def1f0b448d118b59b2e5f68019d37d8833 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E5=AD=99=E5=8D=93=E8=AF=86?= <sunzhuoshi@gmail.com>
Date: Sun, 16 Jan 2022 03:38:33 +0800
Subject: [PATCH] Add config option `windows.appendAtomically`
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Atomic append on windows is only supported on local disk files, and it may
cause errors in other situations, e.g. network file system. If that is the
case, this config option should be used to turn atomic append off.

Co-Authored-By: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: 孙卓识 <sunzhuoshi@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 Documentation/config.txt         |  2 ++
 Documentation/config/windows.txt |  4 ++++
 compat/mingw.c                   | 36 +++++++++++++++++++++++++++++---
 3 files changed, 39 insertions(+), 3 deletions(-)
 create mode 100644 Documentation/config/windows.txt

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 8c0b3ed8075214..f1510a85205487 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -554,4 +554,6 @@ include::config/versionsort.txt[]
 
 include::config/web.txt[]
 
+include::config/windows.txt[]
+
 include::config/worktree.txt[]
diff --git a/Documentation/config/windows.txt b/Documentation/config/windows.txt
new file mode 100644
index 00000000000000..fdaaf1c65504f3
--- /dev/null
+++ b/Documentation/config/windows.txt
@@ -0,0 +1,4 @@
+windows.appendAtomically::
+	By default, append atomic API is used on windows. But it works only with
+	local disk files, if you're working on a network file system, you should
+	set it false to turn it off.
diff --git a/compat/mingw.c b/compat/mingw.c
index 0e851ecae29b90..956ffa5182b289 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -20,6 +20,7 @@
 #include "gettext.h"
 #define SECURITY_WIN32
 #include <sspi.h>
+#include "../repository.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -549,6 +550,7 @@ static int is_local_named_pipe_path(const char *filename)
 
 int mingw_open (const char *filename, int oflags, ...)
 {
+	static int append_atomically = -1;
 	typedef int (*open_fn_t)(wchar_t const *wfilename, int oflags, ...);
 	va_list args;
 	unsigned mode;
@@ -565,7 +567,16 @@ int mingw_open (const char *filename, int oflags, ...)
 		return -1;
 	}
 
-	if ((oflags & O_APPEND) && !is_local_named_pipe_path(filename))
+	/*
+	 * Only set append_atomically to default value(1) when repo is initialized
+	 * and fail to get config value
+	 */
+	if (append_atomically < 0 && the_repository && the_repository->commondir &&
+		git_config_get_bool("windows.appendatomically", &append_atomically))
+		append_atomically = 1;
+
+	if (append_atomically && (oflags & O_APPEND) &&
+		!is_local_named_pipe_path(filename))
 		open_fn = mingw_open_append;
 	else
 		open_fn = _wopen;
@@ -714,9 +725,28 @@ ssize_t mingw_write(int fd, const void *buf, size_t len)
 
 		/* check if fd is a pipe */
 		HANDLE h = (HANDLE) _get_osfhandle(fd);
-		if (GetFileType(h) != FILE_TYPE_PIPE)
+		if (GetFileType(h) != FILE_TYPE_PIPE) {
+			if (orig == EINVAL) {
+				wchar_t path[MAX_PATH];
+				DWORD ret = GetFinalPathNameByHandleW(h, path,
+								ARRAY_SIZE(path), 0);
+				UINT drive_type = ret > 0 && ret < ARRAY_SIZE(path) ?
+					GetDriveTypeW(path) : DRIVE_UNKNOWN;
+
+				/*
+				 * The default atomic append causes such an error on
+				 * network file systems, in such a case, it should be
+				 * turned off via config.
+				 *
+				 * `drive_type` of UNC path: DRIVE_NO_ROOT_DIR
+				 */
+				if (DRIVE_NO_ROOT_DIR == drive_type || DRIVE_REMOTE == drive_type)
+					warning("invalid write operation detected; you may try:\n"
+						"\n\tgit config windows.appendAtomically false");
+			}
+
 			errno = orig;
-		else if (orig == EINVAL)
+		} else if (orig == EINVAL)
 			errno = EPIPE;
 		else {
 			DWORD buf_size;