linux-kernel - Re: Splicing to/from a tty

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Message-ID: <20210120191116.GC740243@zeniv-ca>
Date:   Wed, 20 Jan 2021 19:11:16 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Johannes Berg <johannes@...solutions.net>,
        Oliver Giles <ohw.giles@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: Splicing to/from a tty

On Wed, Jan 20, 2021 at 04:26:08PM +0000, Al Viro wrote:

> [1] yes, it is possible to have O_APPEND opened pipes - open a FIFO with
> O_APPEND and you've got it.  We are not quite consistent in handling
> those - sendfile() to such is rejected, splice() is not.

BTW, according to manpages of splice(2) and sendfile(2), we have
       EINVAL [snip] target file is opened in append mode [snip]
and
       EINVAL out_fd has the O_APPEND flag set.  This is not currently supported by sendfile().

However, splice(2) to FIFO opened with O_APPEND works just fine.  So
it doesn't match the manpage either.

Why do we care about O_APPEND on anything without FMODE_PWRITE (including
pipes), anyway?  All writes there ignore position, after all...