fix: keep mtime when utimens only updates atime (UTIME_OMIT)

sshfs.c

@@ -2873,28 +2873,52 @@ static void sshfs_inc_modifver(void)
 	pthread_mutex_unlock(&sshfs.lock);
 }
 
+static int sshfs_getattr(const char *path, struct stat *stbuf,
+			 struct fuse_file_info *fi);
+
+/*
+ * SSH_FILEXFER_ATTR_ACMODTIME always sets both atime and mtime, so a time the
+ * caller wants left alone (UTIME_OMIT) has to be sent as its current value.
+ * Treating it as "now" makes an atime-only update (e.g. Finder recording that
+ * a file was previewed) overwrite the file's modification time.
+ */
+static time_t utimens_resolve(const struct timespec *ts, time_t cur, time_t now)
+{
+	if (ts->tv_nsec == UTIME_OMIT)
+		return cur;
+	if (ts->tv_nsec == UTIME_NOW)
+		return now;
+	return ts->tv_sec;
+}
+
 static int sshfs_utimens(const char *path, const struct timespec tv[2],
 			 struct fuse_file_info *fi)
 {
-	(void) fi;
 	int err;
 	struct buffer buf;
 	struct sshfs_file *sf = NULL;
-	time_t asec = tv[0].tv_sec, msec = tv[1].tv_sec;
+	struct stat cur;
+	time_t now = time(NULL);
+	time_t asec, msec;
 
-	struct timeval now;
-	gettimeofday(&now, NULL);
-	if (asec == 0)
-		asec = now.tv_sec;
-	if (msec == 0)
-		msec = now.tv_sec;
+	if (tv[0].tv_nsec == UTIME_OMIT && tv[1].tv_nsec == UTIME_OMIT)
+		return 0;
 
 	if (fi != NULL) {
 		sf = get_sshfs_file(fi);
 		if (!sshfs_file_is_conn(sf))
 			return -EIO;
 	}
 
+	memset(&cur, 0, sizeof(cur));
+	if (tv[0].tv_nsec == UTIME_OMIT || tv[1].tv_nsec == UTIME_OMIT) {
+		err = sshfs_getattr(path, &cur, fi);
+		if (err)
+			return err;
+	}
+	asec = utimens_resolve(&tv[0], cur.st_atime, now);
+	msec = utimens_resolve(&tv[1], cur.st_mtime, now);
+
 	buf_init(&buf, 0);
 	if (sf == NULL)
 		buf_add_path(&buf, path);

test/test_sshfs.py

@@ -162,6 +162,7 @@ def test_sshfs(
         # file timestamps.
         tst_utimens(mnt_dir, tol=1)
         tst_utimens_now(mnt_dir)
+        tst_utimens_omit(mnt_dir)
 
         tst_link(mnt_dir, cache_timeout)
         tst_truncate_path(mnt_dir)
@@ -698,6 +699,23 @@ def tst_utimens_now(mnt_dir):
     assert fstat.st_mtime != 0
 
 
+def tst_utimens_omit(mnt_dir):
+    # Updating only the access time (UTIME_OMIT for mtime) must leave the
+    # modification time alone instead of setting it to "now".
+    fullname = pjoin(mnt_dir, name_generator())
+
+    fd = os.open(fullname, os.O_CREAT | os.O_RDWR)
+    os.close(fd)
+    old = int(os.lstat(fullname).st_mtime) - 1000
+    os.utime(fullname, (old, old))
+
+    subprocess.check_call(["touch", "-a", fullname])
+
+    fstat = os.lstat(fullname)
+    assert fstat.st_mtime == old
+    assert fstat.st_atime > old
+
+
 def tst_passthrough(src_dir, mnt_dir, cache_timeout):
     name = name_generator()
     src_name = pjoin(src_dir, name)