Re: [PATCH] eventfs: Stop using dcache_readdir() for getdents()

From: Linus Torvalds <torvalds@linux-foundation.org>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	 Linux Trace Kernel <linux-trace-kernel@vger.kernel.org>,
	Masami Hiramatsu <mhiramat@kernel.org>,
	 Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
	Al Viro <viro@zeniv.linux.org.uk>,
	 Christian Brauner <brauner@kernel.org>,
	linux-fsdevel@vger.kernel.org,
	 Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Subject: Re: [PATCH] eventfs: Stop using dcache_readdir() for getdents()
Date: Wed, 3 Jan 2024 14:06:45 -0800	[thread overview]
Message-ID: <CAHk-=wgJouS5fWAf7ReooLLES0rq2F=V1s-fPyLDX+OoXX+JBw@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wh5kkk2+JAv_D1fm8t1SOpTQyb4n7zuMuVSBG094HH7gA@mail.gmail.com>

On Wed, 3 Jan 2024 at 13:54, Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> Here's an updated patch that builds, and is PURELY AN EXAMPLE.

Oh, and while doing this patch, I found another bug in tracefs,
although it happily is one that doesn't have any way to trigger.

Tracefs has code like this:

        if (dentry->d_inode->i_mode & S_IFDIR) {

and that's very wrong. S_IFDIR is not a bitmask, it's a value that is
part of S_IFMT.

The reason this bug doesn't have any way to trigger is that I think
tracefs can only have S_IFMT values of S_IFDIR and S_IFREG, and those
happen to not have any bits in common, so doing it as a bit test is
wrong, but happens to work.

The test *should* be done as

        if (S_ISDIR(dentry->d_inode->i_mode)) {

(note "IS" vs "IF" - not the greatest user experience ever, but hey,
it harkens back to Ye Olden Times).

                Linus