Make core.sharedRepository work under cygwin 1.7

When core.sharedRepository is used, set_shared_perm() in path.c
needs lstat() to return the correct POSIX permissions.

The default for cygwin is core.ignoreCygwinFSTricks = false, which
means that the fast implementation in do_stat() is used instead of
lstat().

lstat() under cygwin uses the Windows security model to implement
POSIX-like permissions.  The user, group or everyone bits can be set
individually.

do_stat() simplifes the file permission bits, and may return a wrong
value.  The read-only attribute of a file is used to calculate the
permissions, resulting in either rw-r--r-- or r--r--r--

One effect of the simplified do_stat() is that t1301 fails.

Add a function cygwin_get_st_mode_bits() which returns the POSIX
permissions.  When not compiling for cygwin, true_mode_bits() in
path.c is used.

Side note:

t1301 passes under cygwin 1.5.

The "user write" bit is synchronized with the "read only" attribute
of a file:

    $ chmod 444 x
    $ attrib x
    A    R     C:\temp\pt\x

    cygwin 1.7 would show
    A          C:\temp\pt\x

Signed-off-by: Torsten Bögershausen <tboegi@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

compat/cygwin.c

@@ -1,3 +1,4 @@
+#define CYGWIN_C
 #define WIN32_LEAN_AND_MEAN
 #ifdef CYGWIN_V15_WIN32API
 #include "../git-compat-util.h"
@@ -10,6 +11,18 @@
 #endif
 #include "../cache.h" /* to read configuration */
 
+/*
+ * Return POSIX permission bits, regardless of core.ignorecygwinfstricks
+ */
+int cygwin_get_st_mode_bits(const char *path, int *mode)
+{
+	struct stat st;
+	if (lstat(path, &st) < 0)
+		return -1;
+	*mode = st.st_mode;
+	return 0;
+}
+
 static inline void filetime_to_timespec(const FILETIME *ft, struct timespec *ts)
 {
 	long long winTime = ((long long)ft->dwHighDateTime << 32) +

compat/cygwin.h

@@ -4,6 +4,11 @@
 typedef int (*stat_fn_t)(const char*, struct stat*);
 extern stat_fn_t cygwin_stat_fn;
 extern stat_fn_t cygwin_lstat_fn;
+int cygwin_get_st_mode_bits(const char *path, int *mode);
 
+#define get_st_mode_bits(p,m) cygwin_get_st_mode_bits((p),(m))
+#ifndef CYGWIN_C
+/* cygwin.c needs the original lstat() */
 #define stat(path, buf) (*cygwin_stat_fn)(path, buf)
 #define lstat(path, buf) (*cygwin_lstat_fn)(path, buf)
+#endif

git-compat-util.h

@@ -163,6 +163,7 @@
 typedef long intptr_t;
 typedef unsigned long uintptr_t;
 #endif
+int get_st_mode_bits(const char *path, int *mode);
 #if defined(__CYGWIN__)
 #undef _XOPEN_SOURCE
 #include <grp.h>

path.c

@@ -14,6 +14,22 @@
 #include "strbuf.h"
 #include "string-list.h"
 
+#ifndef get_st_mode_bits
+/*
+ * The replacement lstat(2) we use on Cygwin is incomplete and
+ * may return wrong permission bits. Most of the time we do not care,
+ * but the callsites of this wrapper do care.
+ */
+int get_st_mode_bits(const char *path, int *mode)
+{
+	struct stat st;
+	if (lstat(path, &st) < 0)
+		return -1;
+	*mode = st.st_mode;
+	return 0;
+}
+#endif
+
 static char bad_path[] = "/bad-path/";
 
 static char *get_pathname(void)
@@ -391,7 +407,6 @@ const char *enter_repo(const char *path, int strict)
 
 int set_shared_perm(const char *path, int mode)
 {
-	struct stat st;
 	int tweak, shared, orig_mode;
 
 	if (!shared_repository) {
@@ -400,9 +415,8 @@ int set_shared_perm(const char *path, int mode)
 		return 0;
 	}
 	if (!mode) {
-		if (lstat(path, &st) < 0)
+		if (get_st_mode_bits(path, &mode) < 0)
 			return -1;
-		mode = st.st_mode;
 		orig_mode = mode;
 	} else
 		orig_mode = 0;