Merge branch 'optionally-dont-append-atomically-on-windows'

Fix append failure issue under remote directories #2753

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Documentation/config.txt

@@ -545,4 +545,6 @@ include::config/versionsort.txt[]
 
 include::config/web.txt[]
 
+include::config/windows.txt[]
+
 include::config/worktree.txt[]

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.

compat/mingw.c

@@ -19,6 +19,7 @@
 #include "gettext.h"
 #define SECURITY_WIN32
 #include <sspi.h>
+#include "../repository.h"
 
 #define HCAST(type, handle) ((type)(intptr_t)handle)
 
@@ -545,6 +546,7 @@ 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;
@@ -561,7 +563,16 @@ 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;
@@ -710,8 +721,26 @@ ssize_t mingw_write(int fd, const void *buf, size_t len)
 		HANDLE h = (HANDLE) _get_osfhandle(fd);
 		if (GetFileType(h) == FILE_TYPE_PIPE)
 			errno = EPIPE;
-		else
+		else {
+			wchar_t path[MAX_LONG_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 = EINVAL;
+		}
 	}
 
 	return result;