From eecf3977a5d9d2788c0b7d47e2d268708551d4d7 Mon Sep 17 00:00:00 2001
From: Augustin Cavalier <waddlesplash@gmail.com>
Date: Wed, 26 Jan 2022 13:25:11 -0500
Subject: [PATCH] libroot_build: Implement FD writing STAT_ACCESS_TIME and
 STAT_MODIFICATION_TIME.

We have used and had fallback futimens() implementations in libroot_build
(and in this file even) for over a decade, but nobody seems to have noticed
this bit of missing functionality which can be implemented with them.

In fact, this is rather important bit of functionality, as "copyattr"
relies on it to preserve the mtimes of copied files; and we use
recursive copyattr many places in Haiku builds. Thus, the lack of
an implementation here was the cause of all files in built Haiku images
having timestamps of whenever the build was done, and not whenever
the file was actually modified.

This should make development on Haiku nightlies much more pleasant,
as the system headers from the haiku_devel package should no longer
have always-current timestamps with every upgrade.
---
 src/build/libroot/fs.cpp | 28 ++++++++++++++++++----------
 1 file changed, 18 insertions(+), 10 deletions(-)

diff --git a/src/build/libroot/fs.cpp b/src/build/libroot/fs.cpp
index 149c8c054f..8b0c88c4a3 100644
--- a/src/build/libroot/fs.cpp
+++ b/src/build/libroot/fs.cpp
@@ -891,7 +891,6 @@ _kern_write_stat(int fd, const char *path, bool traverseLink,
 			return errno;
 
 		isSymlink = S_ISLNK(tmpStat.st_mode);
-
 	} else {
 		Descriptor *descriptor = get_descriptor(fd);
 		if (!descriptor)
@@ -900,17 +899,14 @@ _kern_write_stat(int fd, const char *path, bool traverseLink,
 		if (FileDescriptor *fileFD
 				= dynamic_cast<FileDescriptor*>(descriptor)) {
 			realFD = fileFD->fd;
-
 		} else if (dynamic_cast<DirectoryDescriptor*>(descriptor)) {
 			error = get_path(fd, NULL, realPath);
 			if (error != B_OK)
 				return error;
-
 		} else if (SymlinkDescriptor *linkFD
 				= dynamic_cast<SymlinkDescriptor*>(descriptor)) {
 			realPath = linkFD->path;
 			isSymlink = true;
-
 		} else
 			return B_FILE_ERROR;
 	}
@@ -941,15 +937,27 @@ _kern_write_stat(int fd, const char *path, bool traverseLink,
 				return errno;
 		}
 
-		// The timestamps can only be set via utime(), but that requires a
-		// path we don't have.
-		if (statMask & (B_STAT_ACCESS_TIME | B_STAT_MODIFICATION_TIME
-				| B_STAT_CREATION_TIME | B_STAT_CHANGE_TIME)) {
-			return B_ERROR;
+		if (statMask & (B_STAT_ACCESS_TIME | B_STAT_MODIFICATION_TIME)) {
+			// Grab the previous mod and access times so we only overwrite
+			// the specified time and not both
+			struct stat oldStat;
+			if (~statMask & (B_STAT_ACCESS_TIME | B_STAT_MODIFICATION_TIME)) {
+				if (fstat(realFD, &oldStat) < 0)
+					return errno;
+			}
+
+			struct timespec times[2];
+			times[0] = (statMask & B_STAT_ACCESS_TIME) ? st->st_atim : oldStat.st_atim;
+			times[1] = (statMask & B_STAT_MODIFICATION_TIME) ? st->st_mtim : oldStat.st_mtim;
+			if (futimens(realFD, times) < 0)
+				return errno;
 		}
 
-		return 0;
+		// not supported
+		if (statMask & (B_STAT_CREATION_TIME | B_STAT_CHANGE_TIME))
+			return B_ERROR;
 
+		return 0;
 	} else {
 		if (statMask & B_STAT_MODE) {
 			if (chmod(realPath.c_str(), st->st_mode) < 0)