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

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Message-ID: <b925ce4f-e9a4-92e6-6a95-6c718cfcb134@google.com>
Date:   Wed, 2 Mar 2022 12:17:30 -0800 (PST)
From:   Hugh Dickins <hughd@...gle.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Xavier Roche <xavier.roche@...olia.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Hugh Dickins <hughd@...gle.com>,
        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, 2 Mar 2022, Linus Torvalds wrote:
> On Mon, Feb 28, 2022 at 12:43 AM Xavier Roche <xavier.roche@...olia.com> wrote:
> >
> > Various filesystems (including ext4) now support file creation time.
> > This patch adds such support for tmpfs-based filesystems.

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.

> 
> What's the odd huge-page noise in this patch?

That was one of the fixups I added, which akpm is holding in a -fix
patch to be merged in, and maybe he'll include my comment from it:

3. Using shmem_getattr() on other file types than regular requires that
   shmem_is_huge() check type, to stop incorrect HPAGE_PMD_SIZE blksize.

(shmem_getattr() was only on regular files before: Xavier's patch
added it to directories etc, to provide btime for them too; but
shmem_getattr() can also include a dubious adjustment to blksize.)

> 
> Other oddities:
> 
>     Reply-To: b954973a-b8d1-cab8-63bd-6ea8063de3@...gle.com
> 
> WHAT?

No comment from me.

> 
> 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've no investment
in btime myself (my instinctive reaction was, is this thing worth
another 16 bytes of inode space?), but Xavier thought it worth doing,
and Andrew worth taking, so go with the flow.

Ah, Andrew has replied meanwhile, I hope I'm not contradicting!

Hugh