utimes doesn't seem to support subseconds times

[arcanis]

• Version: 10.7.0 / 8.11.3
• Platform: OSX & Linux
• Subsystem: fs

Not sure if it's an implementation issue or a documentation issue, but the following is unexpected:

> var d = new Date(1234567891234);

> fs.utimesSync('./test', d, d);
> fs.statSync('./test').mtimeMs
1234567891000

> fs.futimesSync(fs.openSync('./test', 'w'), d, d);
> fs.statSync('./test').mtimeMs
1234567891234

As you can see, the precision is lost (my systems support subsecond precisions - touch manages to change them, and both the stat utility and fs.stat can read them without issues).

The Node documentation also doesn't mention that utimes has a different behavior from futimes (it actually suggest they share the exact same behavior, since futimes redirect to utimes), except possibly in this archived post.

Additionally, the function name (utimes) seem to match the behavior of 2 utime instead of 3 utimes, which seems counterintuitive. The libuv implementation is called uv_fs_utime , which at least hints at the difference of behavior (except that they use uv_fs_futime instead of uv_fs_futimes ..).

[Fishrock123]

@arcanis Are you sure this affects Linux? What version of MacOS did you test? If you tested one that has APFS, are you sure you aren't running into this MacOS APFS Driver bug? - https://openradar.appspot.com/radar?id=4978184932032512

[arcanis]

@Fishrock123 I'll double check, but I'm pretty sure. Can't say the exact MacOS release, but I don't believe I was affected by the bug you mentioned (simply because touch, stat, and futimes are all working correctly. Additionnally, your link references the full date part being set to a specific value, while in my case only the subsecond part is being zero'd).

Tracking down the issue, it seems to be that the utimes implementation is simply using utime (instead of the real utimes). Weirdly the uv function has the correct name (utime, no s), so I'm not entirely sure where the boggus renaming happens.

node/deps/uv/src/unix/fs.c

Lines 700 to 705 in 537a4ba

	static ssize_t uv__fs_utime(uv_fs_t* req) {
	struct utimbuf buf;
	buf.actime = req->atime;
	buf.modtime = req->mtime;
	return utime(req->path, &buf); /* TODO use utimes() where available */
	}

The utime() system call allows specification of timestamps with a resolution of 1 second. (link)

[Fishrock123]

Yeah, I also saw that while debugging my problem.

I'll try to get a libuv pr up this week.

[Fishrock123]

Libuv PR has been merged: libuv/libuv#1940 - should fix it but never got to actually trying if it solves this. 😅

[cjihrig]

@arcanis can you confirm if your problem is solved with the latest on master (including libuv 1.23.1)?

[Fishrock123]

I can confirm this is fixed. \o/

Fixed in 2790db5#diff-e8b03d17fba605de23431c53172682a5 / #22997 / Node 11.0.0