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From: Linus Torvalds <[email protected]>
To: Jens Axboe <[email protected]>
Cc: Ming Lei <[email protected]>, Andy Lutomirski <[email protected]>,
	Dave Chinner <[email protected]>,
	Matthew Wilcox <[email protected]>,
	Stefan Metzmacher <[email protected]>,
	linux-fsdevel <[email protected]>,
	Linux API Mailing List <[email protected]>,
	io-uring <[email protected]>,
	"[email protected]" <[email protected]>,
	Al Viro <[email protected]>,
	Samba Technical <[email protected]>
Subject: Re: copy on write for splice() from file to pipe?
Date: Fri, 10 Feb 2023 14:35:11 -0800	[thread overview]
Message-ID: <CAHk-=wg3gLL-f6XkQo4vw42Q+ySPrMdprNL1dxNrr3RGHzhnrw@mail.gmail.com> (raw)
In-Reply-To: <[email protected]>

On Fri, Feb 10, 2023 at 2:26 PM Jens Axboe <[email protected]> wrote:
> >
> > (I actually suspect that /dev/zero no longer works as a splice source,
> > since we disabled the whole "fall back to regular IO" that Christoph
> > did in 36e2c7421f02 "fs: don't allow splice read/write without
> > explicit ops").
>
> Yet another one... Since it has a read_iter, should be fixable with just
> adding the generic splice_read.

I actually very consciously did *not* want to add cases of
generic_splice_read() "just because we can".

I've been on a "let's minimize the reach of splice" thing for a while.
I really loved Christoph's patches, even if I may not have been hugely
vocal about it. His getting rid of set/get_fs() got rid of a *lot* of
splice pain.

And rather than try to make everything work with splice that used to
work just because it fell back on read/write, I was waiting for actual
regression reports.

Even when splice fails, a lot of user space then falls back on
read/write, and unless there is some really fundamental reason not to,
I think that's always the right thing to do.

So we do have a number of "add splice_write/splice_read" commits, but
they are hopefully all the result of people actually noticing
breakage.

You can do

     git log --grep=36e2c7421f02

to see at least some of them, and I really don't want to see them
without a "Reported-by" and an actual issue.

Exactly because I'm not all that enamoured with splice any more.

                 Linus

  reply	other threads:[~2023-02-10 22:35 UTC|newest]

Thread overview: 64+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-09 13:55 copy on write for splice() from file to pipe? Stefan Metzmacher
2023-02-09 14:11 ` Matthew Wilcox
2023-02-09 14:29   ` Stefan Metzmacher
2023-02-09 16:41 ` Linus Torvalds
2023-02-09 19:17   ` Stefan Metzmacher
2023-02-09 19:36     ` Linus Torvalds
2023-02-09 19:48       ` Linus Torvalds
2023-02-09 20:33         ` Jeremy Allison
2023-02-10 20:45         ` Stefan Metzmacher
2023-02-10 20:51           ` Linus Torvalds
2023-02-10  2:16   ` Dave Chinner
2023-02-10  4:06     ` Dave Chinner
2023-02-10  4:44       ` Matthew Wilcox
2023-02-10  6:57         ` Dave Chinner
2023-02-10 15:14           ` Andy Lutomirski
2023-02-10 16:33             ` Linus Torvalds
2023-02-10 17:57               ` Andy Lutomirski
2023-02-10 18:19                 ` Jeremy Allison
2023-02-10 19:29                   ` Stefan Metzmacher
2023-02-10 18:37                 ` Linus Torvalds
2023-02-10 19:01                   ` Andy Lutomirski
2023-02-10 19:18                     ` Linus Torvalds
2023-02-10 19:27                       ` Jeremy Allison
2023-02-10 19:42                         ` Stefan Metzmacher
2023-02-10 19:42                         ` Linus Torvalds
2023-02-10 19:54                           ` Stefan Metzmacher
2023-02-10 19:29                       ` Linus Torvalds
2023-02-13  9:07                         ` Herbert Xu
2023-02-10 19:55                       ` Andy Lutomirski
2023-02-10 20:27                         ` Linus Torvalds
2023-02-10 20:32                           ` Jens Axboe
2023-02-10 20:36                             ` Linus Torvalds
2023-02-10 20:39                               ` Jens Axboe
2023-02-10 20:44                                 ` Linus Torvalds
2023-02-10 20:50                                   ` Jens Axboe
2023-02-10 21:14                                     ` Andy Lutomirski
2023-02-10 21:27                                       ` Jens Axboe
2023-02-10 21:51                                         ` Jens Axboe
2023-02-10 22:08                                           ` Linus Torvalds
2023-02-10 22:16                                             ` Jens Axboe
2023-02-10 22:17                                             ` Linus Torvalds
2023-02-10 22:25                                               ` Jens Axboe
2023-02-10 22:35                                                 ` Linus Torvalds [this message]
2023-02-10 22:51                                                   ` Jens Axboe
2023-02-11  3:18                                             ` Ming Lei
2023-02-11  6:17                                               ` Ming Lei
2023-02-11 14:13                                               ` Jens Axboe
2023-02-11 15:05                                                 ` Ming Lei
2023-02-11 15:33                                                   ` Jens Axboe
2023-02-11 18:57                                                     ` Linus Torvalds
2023-02-12  2:46                                                       ` Jens Axboe
2023-02-10  4:47       ` Linus Torvalds
2023-02-10  6:19         ` Dave Chinner
2023-02-10 17:23           ` Linus Torvalds
2023-02-10 17:47             ` Linus Torvalds
2023-02-13  9:28               ` Herbert Xu
2023-02-10 22:41             ` David Laight
2023-02-10 22:51               ` Jens Axboe
2023-02-13  9:30               ` Herbert Xu
2023-02-13  9:25           ` Herbert Xu
2023-02-13 18:01             ` Andy Lutomirski
2023-02-14  1:22               ` Herbert Xu
2023-02-17 23:13                 ` Andy Lutomirski
2023-02-20  4:54                   ` Herbert Xu

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