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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Luc Van Oostenryck <luc.vanoostenryck@gmail.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Sparse Mailing-list <linux-sparse@vger.kernel.org>
Subject: Re: [PATCH 00/11] pragma once: treewide conversion
Date: Sun, 28 Feb 2021 12:00:22 -0800	[thread overview]
Message-ID: <CAHk-=wi54DEScexxpMrO+Q2Nag_Tup+Y5YBHc_9_xGLeRfP8pA@mail.gmail.com> (raw)
In-Reply-To: <YDvwVlG/fqVxVYlQ@localhost.localdomain>

On Sun, Feb 28, 2021 at 11:34 AM Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
> >
> > End result: #pragma is fundamentally less reliable than the
> > traditional #ifdef guard. The #ifdef guard works fine even if you
> > re-read the file for whatever reason, while #pragma relies on some
> > kind of magical behavior.

You continue to not even answer this very fundamental question.

"#pragma once" doesn't seem to have a _single_ actual real advantage.

Everybody already does the optimization of not even opening - much
less reading and re-parsing - headers that have the traditional #ifdef
guard.

And even if you _don't_ do that optimization, the #ifdef guard
fundmentally semantically guarantyees the right behavior.

So the #ifdef guard is
 (a) standard
 (b) simple
 (c) reliable
 (d) traditional

and you have yet to explain a _single_ advantage of "#pragma once".

Why add this incredible churn that has no upside?

So no. We're not using #pragma once unless y9ou can come up with some
very strong argument for it

And no, having to come up with a name for the #ifdef guard is not a
strong argument. It's simply not that complicated.

               Linus

  reply	other threads:[~2021-02-28 20:01 UTC|newest]

Thread overview: 48+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-02-28 16:57 [PATCH 00/11] pragma once: treewide conversion Alexey Dobriyan
2021-02-28 16:58 ` [PATCH 01/11] pragma once: delete include/linux/atm_suni.h Alexey Dobriyan
2021-02-28 19:05   ` Jakub Kicinski
2021-02-28 16:59 ` [PATCH 02/11] pragma once: convert arch/arm/tools/gen-mach-types Alexey Dobriyan
2021-02-28 16:59   ` Alexey Dobriyan
2021-03-01 10:19   ` Russell King - ARM Linux admin
2021-03-01 10:19     ` Russell King - ARM Linux admin
2021-03-02 15:15     ` Alexey Dobriyan
2021-03-02 15:15       ` Alexey Dobriyan
2021-02-28 16:59 ` [PATCH 03/11] pragma once: convert arch/s390/tools/gen_facilities.c Alexey Dobriyan
2021-02-28 17:00 ` [PATCH 04/11] pragma once: convert drivers/gpu/drm/pl111/pl111_nomadik.h Alexey Dobriyan
2021-03-01 14:41   ` Linus Walleij
2021-02-28 17:01 ` [PATCH 05/11] pragma once: convert drivers/scsi/qla2xxx/qla_target.h Alexey Dobriyan
2021-02-28 22:07   ` Bart Van Assche
2021-02-28 17:02 ` [PATCH 06/11] pragma once: convert include/linux/cb710.h Alexey Dobriyan
2021-03-03 23:13   ` Michał Mirosław
2021-02-28 17:02 ` [PATCH 07/11] pragma once: convert kernel/time/timeconst.bc Alexey Dobriyan
2021-02-28 17:03 ` [PATCH 08/11] pragma once: convert scripts/atomic/ Alexey Dobriyan
2021-03-01  7:55   ` Peter Zijlstra
2021-02-28 17:04 ` [PATCH 09/11] pragma once: convert scripts/selinux/genheaders/genheaders.c Alexey Dobriyan
2021-02-28 18:37   ` Paul Moore
2021-02-28 18:57     ` Alexey Dobriyan
2021-02-28 17:05 ` [PATCH 10/11] pragma once: delete few backslashes Alexey Dobriyan
2021-02-28 17:05   ` Alexey Dobriyan
2021-03-01  8:54   ` Ido Schimmel
2021-03-01  8:54     ` Ido Schimmel
2021-03-02 19:00   ` Vineet Gupta
2021-03-02 19:00     ` Vineet Gupta
2021-03-04 14:22   ` Edward Cree
2021-03-04 14:22     ` Edward Cree
2021-03-23 10:09     ` Pavel Machek
2021-03-23 10:09       ` Pavel Machek
2021-02-28 17:05 ` [PATCH 11/11] pragma once: conversion script (in Python 2) Alexey Dobriyan
2021-02-28 17:11 ` [PATCH 12/11] pragma once: scripted treewide conversion Alexey Dobriyan
2021-02-28 17:11   ` Alexey Dobriyan
2021-03-01 17:35   ` Darrick J. Wong
2021-02-28 17:46 ` [PATCH 00/11] pragma once: " Linus Torvalds
2021-02-28 19:34   ` Alexey Dobriyan
2021-02-28 20:00     ` Linus Torvalds [this message]
     [not found]       ` <877dmo10m3.fsf@tromey.com>
2021-03-03 20:17         ` Linus Torvalds
2021-03-04 13:55           ` David Laight
2021-03-04 20:16             ` Linus Torvalds
2021-03-05  9:19               ` David Laight
2021-03-05 21:23                 ` Linus Torvalds
2021-03-06 13:07                   ` Miguel Ojeda
2021-03-06 21:33                     ` Linus Torvalds
2021-03-23 10:03               ` Pavel Machek
2021-03-01  0:29     ` Luc Van Oostenryck

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