From: Linus Torvalds <torvalds@linux-foundation.org>
To: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Steven Rostedt <rostedt@goodmis.org>,
LKML <linux-kernel@vger.kernel.org>,
Linux Trace Devel <linux-trace-devel@vger.kernel.org>,
Masami Hiramatsu <mhiramat@kernel.org>,
Christian Brauner <brauner@kernel.org>,
Ajay Kaher <ajay.kaher@broadcom.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH] eventfs: Have inodes have unique inode numbers
Date: Mon, 29 Jan 2024 10:58:30 -0800 [thread overview]
Message-ID: <CAHk-=wg8BrZEzjJ5kUyZzHPZmFqH6ooMN1gRBCofxxCfucgjaw@mail.gmail.com> (raw)
In-Reply-To: <3120f1f0-eaf8-4058-9a65-bdbee28c68c9@efficios.com>
On Mon, 29 Jan 2024 at 08:00, Mathieu Desnoyers
<mathieu.desnoyers@efficios.com> wrote:
>
> This breaks "cp -aH" and "cp -aL".
Do we care? Do we have a user that cares? Has anybody ever hit it?
Why would you ever do anything like that to tracefs filesystem?
In other words: my point is that tracefs just isn't a regular
filesystem. Never was, never will be.
And people should be *aware* of that. We should not say "hey, if it
doesn't work like a normal filesystem, it's a bug".
Try "cp -aL" on /proc, and guess what? It won't work all that well
either. For entirely *different* reasons. You'll get some variation of
"Input/output error"s, and insanely big files and quite possibly
you'll end up with recursive copying as you try to copy the file that
is /proc/self/fd/<output>.
It's just a nonsensical operation to do, and if somebody says "I can't
copy /proc on my system" it's a PEBKAC, not a kernel problem.
The "no regressions" rule is not about made-up "if I do this, behavior changes".
The "no regressions" rule is about *users*.
If you have an actual user that has been doing insane things, and we
change something, and now the insane thing no longer works, at that
point it's a regression, and we'll sigh, and go "Users are insane" and
have to fix it.
But if you have some random test that now behaves differently, it's
not a regression. It's a *warning* sign, sure: tests are useful.
So tests can show when something user-visible changed, and as such
they are a "there be monsters here" sign that maybe some user
experience will hit it too.
So I agree that "just use the same inode number" changes behavior. I
agree that it can be a bit of a danger. But these "look, I can see a
difference" isn't an argument.
And honestly, I have now spent *days* looking at tracefs, and I'm
finding core fundamental bugs that would cause actual oopses and/or
wild pointer accesses.
All of which makes me go "this code needs to be simpler and *cleaner*
and stop making problems".
In other words: tracefs is such a complete mess that I do not care one
*whit* about "cp -aL". I care about "this is actual kernel
instability".
Linus
next prev parent reply other threads:[~2024-01-29 18:58 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-01-26 20:02 [PATCH] eventfs: Have inodes have unique inode numbers Steven Rostedt
2024-01-26 20:25 ` Linus Torvalds
2024-01-26 21:26 ` Steven Rostedt
2024-01-26 21:31 ` Linus Torvalds
2024-01-26 21:43 ` Steven Rostedt
2024-01-26 21:36 ` Linus Torvalds
2024-01-26 21:42 ` Steven Rostedt
2024-01-26 21:49 ` Linus Torvalds
2024-01-26 22:08 ` Steven Rostedt
2024-01-26 22:26 ` Linus Torvalds
2024-01-27 14:47 ` Steven Rostedt
2024-01-28 14:42 ` Steven Rostedt
2024-01-26 22:14 ` Mathieu Desnoyers
2024-01-26 22:29 ` Linus Torvalds
2024-01-26 22:41 ` Mathieu Desnoyers
2024-01-26 22:49 ` Linus Torvalds
2024-01-29 16:00 ` Mathieu Desnoyers
2024-01-29 18:58 ` Linus Torvalds [this message]
2024-01-26 22:34 ` Matthew Wilcox
2024-01-26 22:40 ` Mathieu Desnoyers
2024-01-26 22:48 ` Linus Torvalds
2024-01-26 23:04 ` Matthew Wilcox
2024-01-26 23:11 ` Linus Torvalds
2024-01-26 23:17 ` Linus Torvalds
2024-01-27 9:36 ` Andreas Schwab
2024-01-27 21:47 ` Linus Torvalds
2024-01-28 20:15 ` Steven Rostedt
2024-01-28 20:53 ` Linus Torvalds
2024-01-28 21:08 ` Linus Torvalds
2024-01-28 22:01 ` Steven Rostedt
2024-01-28 22:17 ` Linus Torvalds
2024-01-28 22:26 ` Steven Rostedt
2024-01-28 21:11 ` Steven Rostedt
2024-01-28 21:19 ` Steven Rostedt
2024-01-28 21:43 ` Linus Torvalds
2024-01-28 22:07 ` Linus Torvalds
2024-01-28 22:17 ` Steven Rostedt
2024-01-28 22:25 ` Linus Torvalds
2024-01-28 22:51 ` Steven Rostedt
2024-01-28 23:24 ` Linus Torvalds
2024-01-28 23:59 ` Steven Rostedt
2024-01-29 0:21 ` Steven Rostedt
2024-01-29 1:00 ` Linus Torvalds
2024-01-29 1:42 ` Linus Torvalds
2024-01-29 2:32 ` Steven Rostedt
2024-01-29 3:40 ` Steven Rostedt
2024-01-29 4:01 ` Linus Torvalds
2024-01-29 2:09 ` Steven Rostedt
2024-01-29 6:44 ` Amir Goldstein
2024-01-29 9:32 ` Steven Rostedt
2024-01-27 15:26 ` David Laight
2024-01-27 20:01 ` Linus Torvalds
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