Albert Barnes Commentary 1 Chronicles 9:18

"who hitherto [waited] in the king`s gate eastward: they were the porters for the camp of the children of Levi." — 1 Chronicles 9:18 (ASV)

Who until now waited - This should be translated: “Who to this day waits. These were the porters in the stations of the sons of Levi.” The first clause refers to Shallum, implying that while his house originally had general oversight of the temple gates, a change had occurred by the time the author wrote, leaving Shallum in charge of only the east gate.

The second clause means that these were the gatekeepers at the fixed stations of the Temple's outer gates. These stations corresponded to the camp posts where the Levites guarded the tabernacle in earlier times.