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From: Al Viro <viro@zeniv-ca>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Johannes Berg <johannes@sipsolutions.net>,
	Christoph Hellwig <hch@lst.de>,
	Oliver Giles <ohw.giles@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	Al Viro <viro@zeniv.linux.org.uk>
Subject: Re: Splicing to/from a tty
Date: Mon, 18 Jan 2021 19:45:45 +0000	[thread overview]
Message-ID: <20210118194545.GB736435@zeniv-ca> (raw)
In-Reply-To: <CAHk-=wiiqjO5c_JK5-jW6=JzxoQ26uNHyKtbJfTW+6Ryw9Sv9w@mail.gmail.com>

On Mon, Jan 18, 2021 at 11:26:00AM -0800, Linus Torvalds wrote:
> On Mon, Jan 18, 2021 at 12:58 AM Johannes Berg
> <johannes@sipsolutions.net> wrote:
> >
> > > I think just wiring up iter_file_splice_write would work.  Al?
> >
> > Seems to work for the simple test case that I had, at least:
> 
> Mind sending me a signed-off patch for this?
> 
> Yeah, I know it's a trivial one-liner, but I much prefer having an
> author with a patch and a sign-off to just doing it personally and
> reaping all that glory for it..

IMO it's a wrong way to handle that.   Look: do_sendfile() calls
do_splice_direct(), which calls splice_direct_to_actor().  There
we allocate an internal pipe and go through "feed from source into
that pipe, then shove what's there into destination".  Which is
insane for the case when destination (or source, for that matter)
is a pipe itself.

do_splice_direct() does something that do_splice() won't - it
handles non-pipe to non-pipe case.  Which is how sendfile(2) is
normally used, of course.

I'll look into that in more details, but IMO bothering with
internal pipe is just plain wrong for those cases.

  reply	other threads:[~2021-01-18 19:52 UTC|newest]

Thread overview: 65+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-01-16  7:35 Splicing to/from a tty Oliver Giles
2021-01-16 16:46 ` Johannes Berg
2021-01-17  6:12   ` Oliver Giles
2021-01-18  8:53   ` Christoph Hellwig
2021-01-18  8:58     ` Johannes Berg
2021-01-18 19:26       ` Linus Torvalds
2021-01-18 19:45         ` Al Viro [this message]
2021-01-18 19:49           ` Linus Torvalds
2021-01-18 19:56             ` Al Viro
2021-01-24 19:11           ` Linus Torvalds
2021-01-25  9:16             ` [PATCH] fs/pipe: allow sendfile() to pipe again Johannes Berg
2021-01-25 10:16               ` Christoph Hellwig
2021-01-25 20:34               ` Linus Torvalds
2021-01-26  6:07             ` Splicing to/from a tty Al Viro
2021-01-26  6:08               ` [PATCH 1/3] do_splice_to(): move the logics for limiting the read length in Al Viro
2021-01-26  6:09               ` [PATCH 2/3] take the guts of file-to-pipe splice into a helper function Al Viro
2021-01-26  6:09               ` [PATCH 3/3] teach sendfile(2) to handle send-to-pipe directly Al Viro
2021-01-26 18:57                 ` Linus Torvalds
2021-01-26 19:33                   ` Al Viro
2021-01-26 18:49               ` Splicing to/from a tty Linus Torvalds
2021-01-26 19:42                 ` Al Viro
2021-01-18 19:34     ` Al Viro
2021-01-18 19:46       ` Linus Torvalds
2021-01-18 19:54         ` Al Viro
2021-01-20 16:26           ` Al Viro
2021-01-20 19:11             ` Al Viro
2021-01-20 19:27               ` Linus Torvalds
2021-01-20 22:25                 ` David Laight
2021-01-20 23:02                   ` Al Viro
2021-01-20 23:14                 ` Al Viro
2021-01-20 23:40                   ` Linus Torvalds
2021-01-21  0:38                     ` Al Viro
2021-01-21  1:04                       ` Linus Torvalds
2021-01-21  1:45                         ` Al Viro
2021-01-21  3:38                           ` Linus Torvalds
2021-01-21  6:05                             ` Willy Tarreau
2021-01-21  8:04                               ` Johannes Berg
2021-01-21 10:08                         ` David Laight
2021-01-18  8:16 ` Christoph Hellwig
2021-01-18 19:36   ` Linus Torvalds
2021-01-18 20:24     ` Linus Torvalds
2021-01-18 21:35       ` Linus Torvalds
2021-01-18 21:54         ` Linus Torvalds
2021-01-18 22:03           ` Linus Torvalds
2021-01-18 22:20             ` Linus Torvalds
2021-01-19  1:38               ` Linus Torvalds
2021-01-19 11:53                 ` Greg Kroah-Hartman
2021-01-19 16:56                   ` Robert Karszniewicz
2021-01-19 17:10                     ` Robert Karszniewicz
2021-01-19 22:09                     ` Oliver Giles
2021-01-19 17:25                   ` Linus Torvalds
2021-01-19 20:24                   ` Linus Torvalds
2021-01-19 20:38                     ` Christoph Hellwig
2021-01-20  1:25                     ` Oliver Giles
2021-01-20  4:44                       ` Linus Torvalds
2021-01-20  8:15                         ` Oliver Giles
2021-01-21  1:18                         ` tty splice branch (was "Re: Splicing to/from a tty") Linus Torvalds
2021-01-21  8:44                           ` Greg Kroah-Hartman
2021-01-21  8:50                           ` Jiri Slaby
2021-01-21  8:58                             ` Jiri Slaby
2021-01-21 17:52                               ` Linus Torvalds
2021-01-21  8:58                             ` Greg Kroah-Hartman
2021-01-21 17:03                         ` Splicing to/from a tty Robert Karszniewicz
2021-01-21 18:43                           ` Linus Torvalds
2021-01-19 11:52         ` Greg Kroah-Hartman

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