linux-kernel - Re: [Lsf-pc] [LSF TOPIC] statx extensions for subvol/snapshot filesystems & more

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Message-ID: <CAJfpegtUZ4YWhYqqnS_BcKKpwhHvdUsQPQMf4j49ahwAe2_AXQ@mail.gmail.com>
Date: Thu, 22 Feb 2024 13:48:45 +0100
From: Miklos Szeredi <miklos@...redi.hu>
To: Jan Kara <jack@...e.cz>
Cc: Kent Overstreet <kent.overstreet@...ux.dev>, Josef Bacik <josef@...icpanda.com>, 
	linux-kernel@...r.kernel.org, linux-bcachefs@...r.kernel.org, 
	linux-fsdevel@...r.kernel.org, lsf-pc@...ts.linux-foundation.org, 
	linux-btrfs@...r.kernel.org
Subject: Re: [Lsf-pc] [LSF TOPIC] statx extensions for subvol/snapshot
 filesystems & more

On Thu, 22 Feb 2024 at 12:01, Jan Kara <jack@...e.cz> wrote:

> I think for "unique inode identifier" we don't even have to come up with
> new APIs. The file handle + fsid pair is an established way to do this,

Why not uuid?

fsid seems to be just a degraded uuid.   We can do better with statx
and/or statmount.

> fanotify successfully uses this as object identifier and Amir did quite
> some work for this to be usable for vast majority of filesystems (including

Vast majority != all.   Also even uuid is just a statistically unique
identifier, while st_dev was guaranteed to be unique (but not
persistent, like uuid).

If we are going to start fixing userspace, then we better make sure to
use the right interfaces, that won't have issues in the future.

Thanks,
Miklos