linux-kernel - Re: [GIT PULL] iomap: new code for 5.13-rc1

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Date:   Thu, 29 Apr 2021 09:45:39 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:     Christoph Hellwig <hch@....de>,
        "Darrick J. Wong" <djwong@...nel.org>, Jia He <justin.he@....com>,
        Al Viro <viro@...iv.linux.org.uk>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        Dave Chinner <david@...morbit.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Eric Sandeen <sandeen@...deen.net>,
        Andy Shevchenko <andy.shevchenko@...il.com>
Subject: Re: [GIT PULL] iomap: new code for 5.13-rc1

On Wed, Apr 28, 2021 at 11:40 PM Rasmus Villemoes
<linux@...musvillemoes.dk> wrote:
>
> > That also does explain the arguably odd %pD defaults: %pd came first,
> > and then %pD came afterwards.
>
> Eh? 4b6ccca701ef5977d0ffbc2c932430dea88b38b6 added them both at the same
> time.

Ahh, I looked at "git blame", and saw that file_dentry_name() was
added later. But that turns out to have been an additional fix on top,
not actually "later support".

Looking more at that code, I am starting to think that
"file_dentry_name()" simply shouldn't use "dentry_name()" at all.
Despite that shared code origin, and despite that similar letter
choice (lower-vs-upper case), a dentry and a file really are very very
different from a name standpoint.

And it's not the "a filename is the whale pathname, and a dentry has
its own private dentry name" issue. It's really that the 'struct file'
contains a _path_ - which is not just the dentry pointer, but the
'struct vfsmount' pointer too.

So '%pD' really *could* get the real path right (because it has all
the required information) in ways that '%pd' fundamentally cannot.

At the same time, I really don't like printk specifiers to take any
real locks (ie mount_lock or rename_lock), so I wouldn't want them to
use the full  d_path() logic.

                Linus