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From: Linus Torvalds <[email protected]>
To: Ming Lei <[email protected]>
Cc: Jens Axboe <[email protected]>,
	[email protected], [email protected],
	[email protected],
	Alexander Viro <[email protected]>,
	Stefan Hajnoczi <[email protected]>,
	Miklos Szeredi <[email protected]>,
	Bernd Schubert <[email protected]>,
	Nitesh Shetty <[email protected]>,
	Christoph Hellwig <[email protected]>,
	Ziyang Zhang <[email protected]>
Subject: Re: [PATCH 1/4] fs/splice: enhance direct pipe & splice for moving pages in kernel
Date: Sat, 11 Feb 2023 10:57:08 -0800	[thread overview]
Message-ID: <CAHk-=wgTzLjvhzx-XGkgEQmXH6t=8OTFdQyhDgafGdC2n5gOfg@mail.gmail.com> (raw)
In-Reply-To: <Y+e3b+Myg/30hlYk@T590>

On Sat, Feb 11, 2023 at 7:42 AM Ming Lei <[email protected]> wrote:
>
> +/*
> + * Used by source/sink end only, don't touch them in generic
> + * splice/pipe code. Set in source side, and check in sink
> + * side
> + */
> +#define PIPE_BUF_PRIV_FLAG_MAY_READ    0x1000 /* sink can read from page */
> +#define PIPE_BUF_PRIV_FLAG_MAY_WRITE   0x2000 /* sink can write to page */
> +

So this sounds much more sane and understandable, but I have two worries:

 (a) what's the point of MAY_READ? A non-readable page sounds insane
and wrong. All sinks expect to be able to read.

 (b) what about 'tee()' which duplicates a pipe buffer that has
MAY_WRITE? Particularly one that may already have been *partially*
given to something that thinks it can write to it?

So at a minimum I think the tee code then needs to clear that flag.
And I think MAY_READ is nonsense.

          Linus

  reply	other threads:[~2023-02-11 18:57 UTC|newest]

Thread overview: 30+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2023-02-10 15:32 [PATCH 0/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF Ming Lei
2023-02-10 15:32 ` [PATCH 1/4] fs/splice: enhance direct pipe & splice for moving pages in kernel Ming Lei
2023-02-11 15:42   ` Ming Lei
2023-02-11 18:57     ` Linus Torvalds [this message]
2023-02-12  1:39       ` Ming Lei
2023-02-13 20:04         ` Linus Torvalds
2023-02-14  0:52           ` Ming Lei
2023-02-14  2:35             ` Ming Lei
2023-02-14 11:03           ` Miklos Szeredi
2023-02-14 14:35             ` Ming Lei
2023-02-14 15:39               ` Miklos Szeredi
2023-02-15  0:11                 ` Ming Lei
2023-02-15 10:36                   ` Miklos Szeredi
2023-02-10 15:32 ` [PATCH 2/4] fs/splice: allow to ignore signal in __splice_from_pipe Ming Lei
2023-02-10 15:32 ` [PATCH 3/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF Ming Lei
2023-02-11 15:45   ` Jens Axboe
2023-02-11 16:12     ` Ming Lei
2023-02-11 16:52       ` Jens Axboe
2023-02-12  3:22         ` Ming Lei
2023-02-12  3:55           ` Jens Axboe
2023-02-13  1:06             ` Ming Lei
2023-02-11 17:13   ` Jens Axboe
2023-02-12  1:48     ` Ming Lei
2023-02-12  2:42       ` Jens Axboe
2023-02-10 15:32 ` [PATCH 4/4] ublk_drv: support splice based read/write zero copy Ming Lei
2023-02-10 21:54 ` [PATCH 0/4] io_uring: add IORING_OP_READ[WRITE]_SPLICE_BUF Jens Axboe
2023-02-10 22:19   ` Jens Axboe
2023-02-11  5:13   ` Ming Lei
2023-02-11 15:45     ` Jens Axboe
2023-02-14 16:36 ` Stefan Hajnoczi

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