linux-kernel - Re: [PATCH] fs/kernfs: implement STATX

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Message-ID: <CAKPOu+9cPJ_BCctyTEOgS7ghtiL4CV3EANuEZOtsX48XQqWBLA@mail.gmail.com>
Date: Wed, 21 May 2025 22:19:13 +0200
From: Max Kellermann <max.kellermann@...os.com>
To: Tejun Heo <tj@...nel.org>
Cc: Greg KH <gregkh@...uxfoundation.org>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] fs/kernfs: implement STATX_BTIME

On Wed, May 21, 2025 at 6:18 PM Tejun Heo <tj@...nel.org> wrote:
> Isn't this trivially trackable from userspace with udev?

udev doesn't track the birth time of arbitrary cgroups, and I wouldn't
call udev "trivial". How many lines of C code would you need to talk
to udev to find something out and how many CPU cycles does that take?
One statx() is trivial and cheap, and the btime field is exactly meant
for this. It's the dedicated API for exactly this. (I'm going to use
it, even if the rest of the world doesn't.)