linux-kernel - Re: [PATCH RFC 1/3] fs: introduce helper d_path

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Date:   Sat, 8 May 2021 15:17:44 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Jia He <justin.he@....com>, Petr Mladek <pmladek@...e.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Sergey Senozhatsky <senozhatsky@...omium.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>,
        Jonathan Corbet <corbet@....net>,
        Al Viro <viro@....linux.org.uk>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Vasily Gorbik <gor@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "Eric W . Biederman" <ebiederm@...ssion.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Eric Biggers <ebiggers@...gle.com>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-s390 <linux-s390@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH RFC 1/3] fs: introduce helper d_path_fast()

On Sat, May 8, 2021 at 2:06 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> On Sat, May 08, 2021 at 01:39:45PM -0700, Linus Torvalds wrote:
>
> > +static inline int prepend_entries(struct prepend_buffer *b, const struct path *path, const struct path *root, struct mount *mnt)
>
> If anything, s/path/dentry/, since vfsmnt here will be equal to &mnt->mnt all along.

Too subtle for me.

And is it? Because mnt is from

     mnt = real_mount(path->mnt);

earlier, while vfsmount is plain "path->mnt".

> > +                     return 2;               // detached or not attached yet
> > +                     break;
>
> ?

Leftover. Good catch.

> > +             parent = dentry->d_parent;
> > +             prefetch(parent);
> > +             error = prepend_name(b, &dentry->d_name);
> > +             if (error)
> > +                     break;
>
> return error, surely?

Surely. Bad conversion to the separate function where I missed one of
the "break" statements.

> FWIW, if we go that way, I would make that

No arguments against that - I tried to keep it with the same structure
it had when it was inside prepend_path().

Which I obviously wasn't very good at (see your fixes above ;), but it
was *meant* to be a minimal patch with no structural change.

                      Linus