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

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Message-ID: <8028d6c8b484c1867aa0e9f668b658b1cb7e9521.camel@ibm.com>
Date: Thu, 24 Jul 2025 18:30:34 +0000
From: Viacheslav Dubeyko <Slava.Dubeyko@....com>
To: "viro@...iv.linux.org.uk" <viro@...iv.linux.org.uk>
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, 2025-07-23 at 22:25 +0100, Al Viro wrote:
> 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...

Probably, I am missing something in your course of logic. :)

I assume that you are worried about this part:

	/* Unlink destination if it already exists */
	if (d_really_is_positive(new_dentry)) {
		if (d_is_dir(new_dentry))
			res = hfsplus_rmdir(new_dir, new_dentry);
		else
			res = hfsplus_unlink(new_dir, new_dentry);
		if (res)
			return res;
	}

If we have called hfsplus_rmdir() or hfsplus_unlink(), then this action:

> > +	new_dentry->d_fsdata = old_dentry->d_fsdata;

doesn't make sense. Am I correct?

But if we didn't call hfsplus_rmdir() or hfsplus_unlink(), then we still need to
make this assignment. Do I follow your point?

Thanks,
Slava.