linux-ext4 - Re: [PATCH v7 05/18] fsnotify: introduce pre-content permission events

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Message-ID: <20241120-banditen-nimmersatt-e53c268d893a@brauner>
Date: Wed, 20 Nov 2024 12:09:57 +0100
From: Christian Brauner <brauner@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Amir Goldstein <amir73il@...il.com>, 
	Josef Bacik <josef@...icpanda.com>, kernel-team@...com, linux-fsdevel@...r.kernel.org, jack@...e.cz, 
	linux-xfs@...r.kernel.org, linux-btrfs@...r.kernel.org, linux-mm@...ck.org, 
	linux-ext4@...r.kernel.org
Subject: Re: [PATCH v7 05/18] fsnotify: introduce pre-content permission
 events

> But if anybody is really worried about running out of f_mode bits, we
> could almost certainly turn the existing
> 
>         unsigned int f_flags;
> 
> into a bitfield, and make it be something like
> 
>         unsigned int f_flags:26, f_special:6;

I just saw this now. Two points I would like to keep you to keep mind.

I've already mentiond that I've freed up 5 fmode bits so it's not that
we're in immediate danger of running out. Especially since I added
f_ops_flags which contains all flags that are static, i.e., never change
and can simply live in the file operations struct and aren't that
performance sensitive.

I shrunk struct file to three cachelines. And in fact, we have 8 bytes
to use left since I removed f_version. So it really wouldn't be a
problem to simply add a separate u32 f_special member into struct file
without growing it and still leaving a 4 byte hole if it ever comes to
that.