Merge pull request libgit2#4713 from libgit2/ethomson/win_symlinks

Support symlinks on Windows when core.symlinks=true

Author: ethomson

src/CMakeLists.txt

@@ -423,7 +423,7 @@ FILE(GLOB SRC_H
 
 # On Windows use specific platform sources
 IF (WIN32 AND NOT CYGWIN)
-	ADD_DEFINITIONS(-DWIN32 -D_WIN32_WINNT=0x0501)
+	ADD_DEFINITIONS(-DWIN32 -D_WIN32_WINNT=0x0600)
 
 	IF(MSVC)
 		SET(WIN_RC "win32/git2.rc")

src/repository.c

@@ -944,18 +944,20 @@ static int load_config(
 	git_buf config_path = GIT_BUF_INIT;
 	git_config *cfg = NULL;
 
-	assert(repo && out);
+	assert(out);
 
 	if ((error = git_config_new(&cfg)) < 0)
 		return error;
 
-	if ((error = git_repository_item_path(&config_path, repo, GIT_REPOSITORY_ITEM_CONFIG)) == 0)
-		error = git_config_add_file_ondisk(cfg, config_path.ptr, GIT_CONFIG_LEVEL_LOCAL, repo, 0);
+	if (repo) {
+		if ((error = git_repository_item_path(&config_path, repo, GIT_REPOSITORY_ITEM_CONFIG)) == 0)
+			error = git_config_add_file_ondisk(cfg, config_path.ptr, GIT_CONFIG_LEVEL_LOCAL, repo, 0);
 
-	if (error && error != GIT_ENOTFOUND)
-		goto on_error;
+		if (error && error != GIT_ENOTFOUND)
+			goto on_error;
 
-	git_buf_dispose(&config_path);
+		git_buf_dispose(&config_path);
+	}
 
 	if (global_config_path != NULL &&
 		(error = git_config_add_file_ondisk(
@@ -1411,24 +1413,56 @@ static bool is_filesystem_case_insensitive(const char *gitdir_path)
 
 static bool are_symlinks_supported(const char *wd_path)
 {
+	git_config *config = NULL;
 	git_buf path = GIT_BUF_INIT;
 	int fd;
 	struct stat st;
-	int symlinks_supported = -1;
+	bool symlinks = false;
+
+	/*
+	 * To emulate Git for Windows, symlinks on Windows must be explicitly
+	 * opted-in.  We examine the system configuration for a core.symlinks
+	 * set to true.  If found, we then examine the filesystem to see if
+	 * symlinks are _actually_ supported by the current user.  If that is
+	 * _not_ set, then we do not test or enable symlink support.
+	 */
+#ifdef GIT_WIN32
+	git_buf global_buf = GIT_BUF_INIT;
+	git_buf xdg_buf = GIT_BUF_INIT;
+	git_buf system_buf = GIT_BUF_INIT;
+	git_buf programdata_buf = GIT_BUF_INIT;
+
+	git_config_find_global(&global_buf);
+	git_config_find_xdg(&xdg_buf);
+	git_config_find_system(&system_buf);
+	git_config_find_programdata(&programdata_buf);
+
+	if (load_config(&config, NULL,
+	    path_unless_empty(&global_buf),
+	    path_unless_empty(&xdg_buf),
+	    path_unless_empty(&system_buf),
+	    path_unless_empty(&programdata_buf)) < 0)
+		goto done;
+
+	if (git_config_get_bool(&symlinks, config, "core.symlinks") < 0 || !symlinks)
+		goto done;
+#endif
 
 	if ((fd = git_futils_mktmp(&path, wd_path, 0666)) < 0 ||
-		p_close(fd) < 0 ||
-		p_unlink(path.ptr) < 0 ||
-		p_symlink("testing", path.ptr) < 0 ||
-		p_lstat(path.ptr, &st) < 0)
-		symlinks_supported = false;
-	else
-		symlinks_supported = (S_ISLNK(st.st_mode) != 0);
+	    p_close(fd) < 0 ||
+	    p_unlink(path.ptr) < 0 ||
+	    p_symlink("testing", path.ptr) < 0 ||
+	    p_lstat(path.ptr, &st) < 0)
+		goto done;
+
+	symlinks = (S_ISLNK(st.st_mode) != 0);
 
 	(void)p_unlink(path.ptr);
-	git_buf_dispose(&path);
 
-	return symlinks_supported;
+done:
+	git_buf_dispose(&path);
+	git_config_free(config);
+	return symlinks;
 }
 
 static int create_empty_file(const char *path, mode_t mode)

src/win32/posix_w32.c

@@ -29,15 +29,16 @@
 #define IO_REPARSE_TAG_SYMLINK (0xA000000CL)
 #endif
 
+#ifndef SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE
+# define SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE 0x02
+#endif
+
 /* Allowable mode bits on Win32.  Using mode bits that are not supported on
  * Win32 (eg S_IRWXU) is generally ignored, but Wine warns loudly about it
  * so we simply remove them.
  */
 #define WIN32_MODE_MASK (_S_IREAD | _S_IWRITE)
 
-/* GetFinalPathNameByHandleW signature */
-typedef DWORD(WINAPI *PFGetFinalPathNameByHandleW)(HANDLE, LPWSTR, DWORD, DWORD);
-
 unsigned long git_win32__createfile_sharemode =
  FILE_SHARE_READ | FILE_SHARE_WRITE;
 int git_win32__retries = 10;
@@ -393,12 +394,20 @@ int p_readlink(const char *path, char *buf, size_t bufsiz)
 	return (int)bufsiz;
 }
 
-int p_symlink(const char *old, const char *new)
+int p_symlink(const char *target, const char *path)
 {
-	/* Real symlinks on NTFS require admin privileges. Until this changes,
-	 * libgit2 just creates a text file with the link target in the contents.
-	 */
-	return git_futils_fake_symlink(old, new);
+	git_win32_path target_w, path_w;
+	wchar_t *target_p;
+
+	if (git_win32_path_from_utf8(path_w, path) < 0 ||
+		git__utf8_to_16(target_w, MAX_PATH, target) < 0)
+		return -1;
+
+	if (!CreateSymbolicLinkW(path_w, target_w,
+	    SYMBOLIC_LINK_FLAG_ALLOW_UNPRIVILEGED_CREATE))
+		return -1;
+
+	return 0;
 }
 
 struct open_opts {
@@ -598,40 +607,13 @@ int p_getcwd(char *buffer_out, size_t size)
 	return 0;
 }
 
-/*
- * Returns the address of the GetFinalPathNameByHandleW function.
- * This function is available on Windows Vista and higher.
- */
-static PFGetFinalPathNameByHandleW get_fpnbyhandle(void)
-{
-	static PFGetFinalPathNameByHandleW pFunc = NULL;
-	PFGetFinalPathNameByHandleW toReturn = pFunc;
-
-	if (!toReturn) {
-		HMODULE hModule = GetModuleHandleW(L"kernel32");
-
-		if (hModule)
-			toReturn = (PFGetFinalPathNameByHandleW)GetProcAddress(hModule, "GetFinalPathNameByHandleW");
-
-		pFunc = toReturn;
-	}
-
-	assert(toReturn);
-
-	return toReturn;
-}
-
 static int getfinalpath_w(
 	git_win32_path dest,
 	const wchar_t *path)
 {
-	PFGetFinalPathNameByHandleW pgfp = get_fpnbyhandle();
 	HANDLE hFile;
 	DWORD dwChars;
 
-	if (!pgfp)
-		return -1;
-
 	/* Use FILE_FLAG_BACKUP_SEMANTICS so we can open a directory. Do not
 	* specify FILE_FLAG_OPEN_REPARSE_POINT; we want to open a handle to the
 	* target of the link. */
@@ -642,7 +624,7 @@ static int getfinalpath_w(
 		return -1;
 
 	/* Call GetFinalPathNameByHandle */
-	dwChars = pgfp(hFile, dest, GIT_WIN_PATH_UTF16, FILE_NAME_NORMALIZED);
+	dwChars = GetFinalPathNameByHandleW(hFile, dest, GIT_WIN_PATH_UTF16, FILE_NAME_NORMALIZED);
 	CloseHandle(hFile);
 
 	if (!dwChars || dwChars >= GIT_WIN_PATH_UTF16)