Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <C8KER7U60WXE.25UFD8RE6QZQK@oguc> <f184764a283bdf3694478fa35ad41d2b3ec38850.camel@sipsolutions.net>
 <20210118085311.GA2735@lst.de> <20210118193457.GA736435@zeniv-ca>
 <CAHk-=wh6HLz_qMam_J=W3X4caBqAGN8P+8c_y+sGFvBaD70K8w@mail.gmail.com>
 <20210118195400.GC736435@zeniv-ca> <20210120162608.GB740243@zeniv-ca> <20210120191116.GC740243@zeniv-ca>
In-Reply-To: <20210120191116.GC740243@zeniv-ca>
From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Wed, 20 Jan 2021 11:27:26 -0800
Message-ID: <CAHk-=wjtTC_jNL+K1Ey_wY_KpTYZOR5XwhkZ+Eu7vviVi5itDQ@mail.gmail.com>
Subject: Re: Splicing to/from a tty
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Christoph Hellwig <hch@lst.de>,
        Johannes Berg <johannes@sipsolutions.net>,
        Oliver Giles <ohw.giles@gmail.com>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Wed, Jan 20, 2021 at 11:11 AM Al Viro <viro@zeniv.linux.org.uk> wrote:
>
> Why do we care about O_APPEND on anything without FMODE_PWRITE (including
> pipes), anyway?  All writes there ignore position, after all...

We shouldn't care.

Also, I think we should try to move away from FMODE_PWRITE/PREAD
entirely, and use FMODE_STREAM as the primary "this thing doesn't have
a position at all".

That's what gets rid of all the f_pos locking etc after all. The
FMODE_PWRITE/PREAD flags are I think legacy (although we do seem to
have the seq_file case that normally allows position on reads, but not
on writes, so we may need to keep all three bits).

Anyway, I think that with FMODE_STREAM, O_APPEND definitely should be a no-op.

            Linus