Merge pull request #11763 from NixOS/mergify/bp/2.24-maintenance/pr-11751

Add support for `utimensat` as an alternative to `lutimes` (backport #11751)

configure.ac

@@ -89,9 +89,10 @@ AC_LANG_POP(C++)
 AC_CHECK_FUNCS([statvfs pipe2])
 
 
-# Check for lutimes, optionally used for changing the mtime of
+# Check for lutimes and utimensat, optionally used for changing the
-# symlinks.
+# mtime of symlinks.
-AC_CHECK_FUNCS([lutimes])
+AC_CHECK_DECLS([AT_SYMLINK_NOFOLLOW], [], [], [[#include <fcntl.h>]])
+AC_CHECK_FUNCS([lutimes utimensat])
 
 
 # Check whether the store optimiser can optimise symlinks.

src/libutil/file-system.cc

@@ -574,7 +574,28 @@ void setWriteTime(
     time_t modificationTime,
     std::optional<bool> optIsSymlink)
 {
-#ifndef _WIN32
+#ifdef _WIN32
+    // FIXME use `fs::last_write_time`.
+    //
+    // Would be nice to use std::filesystem unconditionally, but
+    // doesn't support access time just modification time.
+    //
+    // System clock vs File clock issues also make that annoying.
+    warn("Changing file times is not yet implemented on Windows, path is '%s'", path);
+#elif HAVE_UTIMENSAT && HAVE_DECL_AT_SYMLINK_NOFOLLOW
+    struct timespec times[2] = {
+        {
+            .tv_sec = accessedTime,
+            .tv_nsec = 0,
+        },
+        {
+            .tv_sec = modificationTime,
+            .tv_nsec = 0,
+        },
+    };
+    if (utimensat(AT_FDCWD, path.c_str(), times, AT_SYMLINK_NOFOLLOW) == -1)
+        throw SysError("changing modification time of '%s' (using `utimensat`)", path);
+#else
     struct timeval times[2] = {
         {
             .tv_sec = accessedTime,
@@ -585,42 +606,21 @@ void setWriteTime(
             .tv_usec = 0,
         },
     };
-#endif
+#if HAVE_LUTIMES
-
+    if (lutimes(path.c_str(), times) == -1)
-    auto nonSymlink = [&]{
+        throw SysError("changing modification time of '%s'", path);
+#else
     bool isSymlink = optIsSymlink
         ? *optIsSymlink
         : fs::is_symlink(path);
 
     if (!isSymlink) {
-#ifdef _WIN32
+        if (utimes(path.c_str(), times) == -1)
-            // FIXME use `fs::last_write_time`.
-            //
-            // Would be nice to use std::filesystem unconditionally, but
-            // doesn't support access time just modification time.
-            //
-            // System clock vs File clock issues also make that annoying.
-            warn("Changing file times is not yet implemented on Windows, path is '%s'", path);
-#else
-            if (utimes(path.c_str(), times) == -1) {
-
             throw SysError("changing modification time of '%s' (not a symlink)", path);
-            }
-#endif
     } else {
         throw Error("Cannot modification time of symlink '%s'", path);
     }
-    };
+#endif
-
-#if HAVE_LUTIMES
-    if (lutimes(path.c_str(), times) == -1) {
-        if (errno == ENOSYS)
-            nonSymlink();
-        else
-            throw SysError("changing modification time of '%s'", path);
-    }
-#else
-    nonSymlink();
 #endif
 }
 

src/libutil/meson.build

@@ -41,6 +41,8 @@ check_funcs = [
   # Optionally used to try to close more file descriptors (e.g. before
   # forking) on Unix.
   'sysconf',
+  # Optionally used for changing the mtime of files and symlinks.
+  'utimensat',
 ]
 foreach funcspec : check_funcs
   define_name = 'HAVE_' + funcspec.underscorify().to_upper()
@@ -48,6 +50,8 @@ foreach funcspec : check_funcs
   configdata.set(define_name, define_value)
 endforeach
 
+configdata.set('HAVE_DECL_AT_SYMLINK_NOFOLLOW', cxx.has_header_symbol('fcntl.h', 'AT_SYMLINK_NOFOLLOW').to_int())
+
 subdir('build-utils-meson/threads')
 
 if host_machine.system() == 'windows'