mingw: Windows Docker volumes are *not* symbolic links

... even if they may look like them.

As looking up the target of the "symbolic link" (just to see whether it
starts with `/ContainerMappedDirectories/`) is pretty expensive, we
do it when we can be *really* sure that there is a possibility that this
might be the case.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: JiSeop Moon <zcube@zcube.kr>

Author: dscho

compat/mingw.c

@@ -982,7 +982,7 @@ int mingw_lstat(const char *file_name, struct stat *buf)
 		buf->st_uid = 0;
 		buf->st_nlink = 1;
 		buf->st_mode = file_attr_to_st_mode(fdata.dwFileAttributes,
-				reparse_tag);
+				reparse_tag, file_name);
 		buf->st_size = S_ISLNK(buf->st_mode) ? link_len :
 			fdata.nFileSizeLow | (((off_t) fdata.nFileSizeHigh) << 32);
 		buf->st_dev = buf->st_rdev = 0; /* not used by Git */
@@ -1033,7 +1033,7 @@ static int get_file_info_by_handle(HANDLE hnd, struct stat *buf)
 	buf->st_gid = 0;
 	buf->st_uid = 0;
 	buf->st_nlink = 1;
-	buf->st_mode = file_attr_to_st_mode(fdata.dwFileAttributes, 0);
+	buf->st_mode = file_attr_to_st_mode(fdata.dwFileAttributes, 0, NULL);
 	buf->st_size = fdata.nFileSizeLow |
 		(((off_t)fdata.nFileSizeHigh)<<32);
 	buf->st_dev = buf->st_rdev = 0; /* not used by Git */
@@ -3729,12 +3729,25 @@ int is_inside_windows_container(void)
 	return inside_container;
 }
 
-int file_attr_to_st_mode (DWORD attr, DWORD tag)
+int file_attr_to_st_mode (DWORD attr, DWORD tag, const char *path)
 {
 	int fMode = S_IREAD;
-	if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) && tag == IO_REPARSE_TAG_SYMLINK)
-		fMode |= S_IFLNK;
-	else if (attr & FILE_ATTRIBUTE_DIRECTORY)
+	if ((attr & FILE_ATTRIBUTE_REPARSE_POINT) &&
+	    tag == IO_REPARSE_TAG_SYMLINK) {
+		int flag = S_IFLNK;
+		char buf[MAX_LONG_PATH];
+
+		/*
+		 * Windows containers' mapped volumes are marked as reparse
+		 * points and look like symbolic links, but they are not.
+		 */
+		if (path && is_inside_windows_container() &&
+		    readlink(path, buf, sizeof(buf)) > 27 &&
+		    starts_with(buf, "/ContainerMappedDirectories/"))
+			flag = S_IFDIR;
+
+		fMode |= flag;
+	} else if (attr & FILE_ATTRIBUTE_DIRECTORY)
 		fMode |= S_IFDIR;
 	else
 		fMode |= S_IFREG;

compat/win32.h

@@ -6,7 +6,7 @@
 #include <windows.h>
 #endif
 
-extern int file_attr_to_st_mode (DWORD attr, DWORD tag);
+extern int file_attr_to_st_mode (DWORD attr, DWORD tag, const char *path);
 
 static inline int get_file_attr(const char *fname, WIN32_FILE_ATTRIBUTE_DATA *fdata)
 {

compat/win32/fscache.c

@@ -200,8 +200,30 @@ static struct fsentry *fseentry_create_entry(struct fscache *cache,
 		fdata->FileAttributes & FILE_ATTRIBUTE_REPARSE_POINT ?
 		fdata->EaSize : 0;
 
+	/*
+	 * On certain Windows versions, host directories mapped into
+	 * Windows Containers ("Volumes", see https://docs.docker.com/storage/volumes/)
+	 * look like symbolic links, but their targets are paths that
+	 * are valid only in kernel mode.
+	 *
+	 * Let's work around this by detecting that situation and
+	 * telling Git that these are *not* symbolic links.
+	 */
+	if (fse->reparse_tag == IO_REPARSE_TAG_SYMLINK &&
+	    sizeof(buf) > (list ? list->len + 1 : 0) + fse->len + 1 &&
+	    is_inside_windows_container()) {
+		size_t off = 0;
+		if (list) {
+			memcpy(buf, list->dirent.d_name, list->len);
+			buf[list->len] = '/';
+			off = list->len + 1;
+		}
+		memcpy(buf + off, fse->dirent.d_name, fse->len);
+		buf[off + fse->len] = '\0';
+	}
+
 	fse->st_mode = file_attr_to_st_mode(fdata->FileAttributes,
-					    fdata->EaSize);
+					    fdata->EaSize, buf);
 	fse->dirent.d_type = S_ISREG(fse->st_mode) ? DT_REG :
 			S_ISDIR(fse->st_mode) ? DT_DIR : DT_LNK;
 	fse->u.s.st_size = S_ISLNK(fse->st_mode) ? MAX_LONG_PATH :