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

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Message-ID: <CAHk-=whZhNXiOGgw8mXG+PTpGvxnRG1v5_GjtjHpoYXd2Fn_Ow@mail.gmail.com>
Date:   Sat, 8 May 2021 13:39:45 -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 12:13 PM Al Viro <viro@...iv.linux.org.uk> wrote:
>
> Potentiallty delicate question is how to pass bptr/blen to the caller
> of that helper...

So I was thinking something like this patch..

THIS IS TOTALLY UNTESTED!

I've basically introduced a "struct prepend_buffer" that acts as that
"end,len" pair and that gets passed around. It builds cleanly for me,
which actually makes me fairly happy that it might even be close
right, because the calling conventions would catch any mistake.

It looks superficially sane to me, but again - untested.

The patch ended up being bigger than I expected, but it's all fairly
straightforward - just munging the calling conventions.

Oh, and I did extract out the core of "prepend_path()" into
"prepend_entries()" just to show how it would work.

              Linus

View attachment "patch.diff" of type "text/x-patch" (11058 bytes)