linux-kernel - Re: [PATCH v4 1/3] hfsplus: fix to update ctime after rename

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Message-ID: <20250723212511.GQ2580412@ZenIV>
Date: Wed, 23 Jul 2025 22:25:11 +0100
From: Al Viro <viro@...iv.linux.org.uk>
To: Viacheslav Dubeyko <Slava.Dubeyko@....com>
Cc: "frank.li@...o.com" <frank.li@...o.com>,
	"glaubitz@...sik.fu-berlin.de" <glaubitz@...sik.fu-berlin.de>,
	"slava@...eyko.com" <slava@...eyko.com>,
	"linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/3] hfsplus: fix to update ctime after rename

On Wed, Jul 23, 2025 at 05:58:01PM +0000, Viacheslav Dubeyko wrote:

> So, this line simply copies CNID from old_dentry->d_fsdata to
> new_dentry->d_fsdata during the rename operation. I assume that
> ->fs_data should be untouched by generic logic of dentries processing.

Yes, I understand that; what I do not understand is why.  Why would
the CNID of renamed object be slapped on dentry of removed target?
I'm trying to understand the logics with link(2) and unlink-of-opened
in that code...

Incidentally, what happens if you
	fd = creat("foo", 0666);
	write(fd, "foo", 3);
	link("foo", "bar");
	unlink("bar");
	close(fd);
The games with S_DEAD in there look odd...