linux-kernel - Re: Testing if two open descriptors refer to the same inode

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Message-ID: <Zqgg1Z9GvPZR93WC@dread.disaster.area>
Date: Tue, 30 Jul 2024 09:08:05 +1000
From: Dave Chinner <david@...morbit.com>
To: Florian Weimer <fweimer@...hat.com>
Cc: Mateusz Guzik <mjguzik@...il.com>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
	Dave Chinner <dchinner@...hat.com>
Subject: Re: Testing if two open descriptors refer to the same inode

On Mon, Jul 29, 2024 at 12:57:14PM +0200, Florian Weimer wrote:
> * Mateusz Guzik:
> 
> > On Mon, Jul 29, 2024 at 12:40:35PM +0200, Florian Weimer wrote:
> >> * Mateusz Guzik:
> >> 
> >> > On Mon, Jul 29, 2024 at 08:55:46AM +0200, Florian Weimer wrote:
> >> >> It was pointed out to me that inode numbers on Linux are no longer
> >> >> expected to be unique per file system, even for local file systems.
> >> >
> >> > I don't know if I'm parsing this correctly.
> >> >
> >> > Are you claiming on-disk inode numbers are not guaranteed unique per
> >> > filesystem? It sounds like utter breakage, with capital 'f'.
> >> 
> >> Yes, POSIX semantics and traditional Linux semantics for POSIX-like
> >> local file systems are different.
> >
> > Can you link me some threads about this?
> 
> Sorry, it was an internal thread.  It's supposed to be common knowledge
> among Linux file system developers.

btrfs has been dealing with this issue since snapshots/subvols were
first introduced some 15-odd years ago. This isn't a new problem...

https://lore.kernel.org/linux-fsdevel/20231025210654.GA2892534@perftesting/

> Aleksa referenced LSF/MM
> discussions.

I also referenced those discussions and the -fsdevel discussions
that have been happening for quite some time. I'll reference some
of them here again, because they are all out in the open....

https://lwn.net/Articles/975444/

https://lore.kernel.org/linux-fsdevel/?q=st_vol

https://lore.kernel.org/linux-fsdevel/20231211233231.oiazgkqs7yahruuw@moria.home.lan/

-Dave.
-- 
Dave Chinner
david@...morbit.com