linux-kernel - Re: [PATCH v3] tmpfs: support for file creation time

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Message-ID: <20220314210849.GA121935@xavier-xps>
Date:   Mon, 14 Mar 2022 22:08:49 +0100
From:   Xavier Roche <xavier.roche@...olia.com>
To:     Hugh Dickins <hughd@...gle.com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Jean Delvare <jdelvare@...e.de>, Linux-MM <linux-mm@...ck.org>
Subject: Re: [PATCH v3] tmpfs: support for file creation time

On Wed, Mar 02, 2022 at 12:17:30PM -0800, Hugh Dickins wrote:
> Please ignore this patch for now: I presume Xavier did not understand
> the "from akpm to Linus in next merge window" flow, and thought he had
> to resend the patch to you.

I will resend a fixed v4 version in a moment, sorry for the noise (and
I indeed did not fully understand the flow).

> > And finally - if we really want to treat btime as a first-class entity
> > and expect things like tmpfs to support it, then we should just bite
> > the bullet and put it in 'struct inode' along with the other times.
> I've no objection if someone does that later.

I might give it a try if this is something that can be of interest.

The idea of having btime in 'struct inode' would make the btime a
first-class citizen, allowing to have more consistent (w.r.t filesystem
types) behavior.

This would also mean allowing to _change_ it, typically to allow archivers
to set the creation time as they do for {a,c,m}time.

Currently, birth time semantic is bound to the current filesystem's
life cycle and as such is irrelevant after a restore, or a 'tar xf'.

The only gray area to me is whether or not we "can" always change this
property without unforeseen consequences, typically for ext4.