linux-kernel - Re: [PATCH] eventfs: Have inodes have unique inode numbers

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Date: Fri, 26 Jan 2024 23:04:34 +0000
From: Matthew Wilcox <willy@...radead.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux Trace Devel <linux-trace-devel@...r.kernel.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Christian Brauner <brauner@...nel.org>,
	Ajay Kaher <ajay.kaher@...adcom.com>,
	Geert Uytterhoeven <geert@...ux-m68k.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] eventfs: Have inodes have unique inode numbers

On Fri, Jan 26, 2024 at 02:48:45PM -0800, Linus Torvalds wrote:
> On Fri, 26 Jan 2024 at 14:34, Matthew Wilcox <willy@...radead.org> wrote:
> >
> > On Fri, Jan 26, 2024 at 05:14:12PM -0500, Mathieu Desnoyers wrote:
> > > I would suggest this straightforward solution to this:
> > >
> > > a) define a EVENTFS_MAX_INODES (e.g. 4096 * 8),
> > >
> > > b) keep track of inode allocation in a bitmap (within a single page),
> > >
> > > c) disallow allocating more than "EVENTFS_MAX_INODES" in eventfs.
> >
> > ... reinventing the IDA?
> 
> Guysm, this is a random number that is *so* interesting that I
> seriously think we shouldn't have it at all.
> 
> End result: nobody should care. Even the general VFS layer doesn't care.
> 
> It literally avoids inode number zero, not because it would be a bad
> inode number, but simply because of some random historical oddity.
> 
> In fact, I don't think we even have a reason for it. We have a commit
> 2adc376c5519 ("vfs: avoid creation of inode number 0 in get_next_ino")
> and that one calls out glibc for not deleting them. That makes no
> sense to me, but whatever.

Maybe we should take advantage of that historical oddity.  All files
in eventfs have inode number 0, problem solved.