Win32: let mingw_lstat() error early upon problems with reparse points

When obtaining lstat information for reparse points, we need to call
FindFirstFile() in addition to GetFileInformationEx() to obtain the type
of the reparse point (symlink, mount point etc.). However, currently there
is no error handling whatsoever if FindFirstFile() fails.

Call FindFirstFile() before modifying the stat *buf output parameter and
error out if the call fails.

Note: The FindFirstFile() return value includes all the data that we get
from GetFileAttributesEx(), so we could replace GetFileAttributesEx() with
FindFirstFile(). We don't do that because GetFileAttributesEx() is about
twice as fast for single files. I.e. we only pay the extra cost of calling
FindFirstFile() in the rare case that we encounter a reparse point.

Note: The indentation of the remaining reparse point code will be fixed in
the next patch.

Signed-off-by: Karsten Blees <blees@dcon.de>

Author: kblees

Diff for: compat/mingw.c

@@ -946,6 +946,7 @@ static int has_valid_directory_prefix(wchar_t *wfilename)
 int mingw_lstat(const char *file_name, struct stat *buf)
 {
 	WIN32_FILE_ATTRIBUTE_DATA fdata;
+	WIN32_FIND_DATAW findbuf = { 0 };
 	wchar_t wfilename[MAX_LONG_PATH];
 	int wlen = xutftowcs_long_path(wfilename, file_name);
 	if (wlen < 0)
@@ -960,6 +961,13 @@ int mingw_lstat(const char *file_name, struct stat *buf)
 	}
 
 	if (GetFileAttributesExW(wfilename, GetFileExInfoStandard, &fdata)) {
+		/* for reparse points, use FindFirstFile to get the reparse tag */
+		if (fdata.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
+			HANDLE handle = FindFirstFileW(wfilename, &findbuf);
+			if (handle == INVALID_HANDLE_VALUE)
+				goto error;
+			FindClose(handle);
+		}
 		buf->st_ino = 0;
 		buf->st_gid = 0;
 		buf->st_uid = 0;
@@ -972,20 +980,16 @@ int mingw_lstat(const char *file_name, struct stat *buf)
 		filetime_to_timespec(&(fdata.ftLastWriteTime), &(buf->st_mtim));
 		filetime_to_timespec(&(fdata.ftCreationTime), &(buf->st_ctim));
 		if (fdata.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) {
-			WIN32_FIND_DATAW findbuf;
-			HANDLE handle = FindFirstFileW(wfilename, &findbuf);
-			if (handle != INVALID_HANDLE_VALUE) {
 				if ((findbuf.dwFileAttributes & FILE_ATTRIBUTE_REPARSE_POINT) &&
 						(findbuf.dwReserved0 == IO_REPARSE_TAG_SYMLINK)) {
 					buf->st_mode = S_IFLNK | S_IREAD;
 					if (!(findbuf.dwFileAttributes & FILE_ATTRIBUTE_READONLY))
 						buf->st_mode |= S_IWRITE;
 				}
-				FindClose(handle);
-			}
 		}
 		return 0;
 	}
+error:
 	switch (GetLastError()) {
 	case ERROR_ACCESS_DENIED:
 	case ERROR_SHARING_VIOLATION: