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From: David Laight <David.Laight@ACULAB.COM>
To: 'Christoph Hellwig' <hch@lst.de>,
	'Catalin Marinas' <catalin.marinas@arm.com>,
	'Will Deacon' <will@kernel.org>,
	"'Thomas Bogendoerfer'" <tsbogend@alpha.franken.de>,
	"'James E.J. Bottomley'" <James.Bottomley@HansenPartnership.com>,
	'Helge Deller' <deller@gmx.de>,
	'Michael Ellerman' <mpe@ellerman.id.au>,
	'Heiko Carstens' <hca@linux.ibm.com>,
	'Vasily Gorbik' <gor@linux.ibm.com>,
	"'Christian Borntraeger'" <borntraeger@de.ibm.com>,
	"'David S. Miller'" <davem@davemloft.net>,
	"'x86@kernel.org'" <x86@kernel.org>,
	'Arnd Bergmann' <arnd@arndb.de>
Cc: "'linux-arch@vger.kernel.org'" <linux-arch@vger.kernel.org>,
	"'linux-s390@vger.kernel.org'" <linux-s390@vger.kernel.org>,
	"'linux-parisc@vger.kernel.org'" <linux-parisc@vger.kernel.org>,
	"'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
	"'linux-mips@vger.kernel.org'" <linux-mips@vger.kernel.org>,
	"'sparclinux@vger.kernel.org'" <sparclinux@vger.kernel.org>,
	"'linuxppc-dev@lists.ozlabs.org'" <linuxppc-dev@lists.ozlabs.org>,
	"'linux-arm-kernel@lists.infradead.org'" 
	<linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH 5/5] compat: consolidate the compat_flock{,64} definition
Date: Mon, 12 Apr 2021 10:53:24 +0000	[thread overview]
Message-ID: <5c3635a2b44a496b88d665e8686d9436@AcuMS.aculab.com> (raw)
In-Reply-To: <15be19af19174c7692dd795297884096@AcuMS.aculab.com>

From: David Laight
> Sent: 12 April 2021 10:37
...
> I'm guessing that compat_pid_t is 16 bits?
> So the native 32bit version has an unnamed 2 byte structure pad.
> The 'packed' removes this pad from the compat structure.
> 
> AFAICT (apart from mips) the __ARCH_COMPAT_FLOCK_PAD is just
> adding an explicit pad for the implicit pad the compiler
> would generate because compat_pid_t is 16 bits.

I've just looked at the header.
compat_pid_t is 32 bits.
So Linux must have gained 32bit pids at some earlier time.
(Historically Unix pids were 16 bit - even on 32bit systems.)

Which makes the explicit pad in 'sparc' rather 'interesting'.

Actually the tail pad can just be removed from the compat
structures.
Just a comment that mips and sparc have extra fields
in the uapi header is enough.

The kernel never needs to read/write the pad.
userspace must provide the pad in case the kernel writes it.

oh - compat_loff_t is only used in a couple of other places.
neither care in any way about the alignment.
(Provided get_user() doesn't fault on a 8n+4 aligned address.)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


WARNING: multiple messages have this Message-ID (diff)
From: David Laight <David.Laight@ACULAB.COM>
To: 'Christoph Hellwig' <hch@lst.de>,
	'Catalin Marinas' <catalin.marinas@arm.com>,
	'Will Deacon' <will@kernel.org>,
	"'Thomas Bogendoerfer'" <tsbogend@alpha.franken.de>,
	"'James E.J. Bottomley'" <James.Bottomley@HansenPartnership.com>,
	'Helge Deller' <deller@gmx.de>,
	'Michael Ellerman' <mpe@ellerman.id.au>,
	'Heiko Carstens' <hca@linux.ibm.com>,
	'Vasily Gorbik' <gor@linux.ibm.com>,
	"'Christian Borntraeger'" <borntraeger@de.ibm.com>,
	"'David S. Miller'" <davem@davemloft.net>,
	"'x86@kernel.org'" <x86@kernel.org>,
	'Arnd Bergmann' <arnd@arndb.de>
Cc: "'linux-arch@vger.kernel.org'" <linux-arch@vger.kernel.org>,
	"'linux-s390@vger.kernel.org'" <linux-s390@vger.kernel.org>,
	"'linux-parisc@vger.kernel.org'" <linux-parisc@vger.kernel.org>,
	"'linux-kernel@vger.kernel.org'" <linux-kernel@vger.kernel.org>,
	"'linux-mips@vger.kernel.org'" <linux-mips@vger.kernel.org>,
	"'sparclinux@vger.kernel.org'" <sparclinux@vger.kernel.org>,
	"'linuxppc-dev@lists.ozlabs.org'" <linuxppc-dev@lists.ozlabs.org>,
	"'linux-arm-kernel@lists.infradead.org'"
	<linux-arm-kernel@lists.infradead.org>
Subject: RE: [PATCH 5/5] compat: consolidate the compat_flock{,64} definition
Date: Mon, 12 Apr 2021 10:53:24 +0000	[thread overview]
Message-ID: <5c3635a2b44a496b88d665e8686d9436@AcuMS.aculab.com> (raw)
In-Reply-To: <15be19af19174c7692dd795297884096@AcuMS.aculab.com>

From: David Laight
> Sent: 12 April 2021 10:37
...
> I'm guessing that compat_pid_t is 16 bits?
> So the native 32bit version has an unnamed 2 byte structure pad.
> The 'packed' removes this pad from the compat structure.
> 
> AFAICT (apart from mips) the __ARCH_COMPAT_FLOCK_PAD is just
> adding an explicit pad for the implicit pad the compiler
> would generate because compat_pid_t is 16 bits.

I've just looked at the header.
compat_pid_t is 32 bits.
So Linux must have gained 32bit pids at some earlier time.
(Historically Unix pids were 16 bit - even on 32bit systems.)

Which makes the explicit pad in 'sparc' rather 'interesting'.

Actually the tail pad can just be removed from the compat
structures.
Just a comment that mips and sparc have extra fields
in the uapi header is enough.

The kernel never needs to read/write the pad.
userspace must provide the pad in case the kernel writes it.

oh - compat_loff_t is only used in a couple of other places.
neither care in any way about the alignment.
(Provided get_user() doesn't fault on a 8n+4 aligned address.)

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)


_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel

  reply	other threads:[~2021-04-12 10:53 UTC|newest]

Thread overview: 60+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-12  8:55 consolidate the flock uapi definitions Christoph Hellwig
2021-04-12  8:55 ` Christoph Hellwig
2021-04-12  8:55 ` Christoph Hellwig
2021-04-12  8:55 ` [PATCH 1/5] uapi: remove the unused HAVE_ARCH_STRUCT_FLOCK64 define Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  9:55   ` Arnd Bergmann
2021-04-12  9:55     ` Arnd Bergmann
2021-04-12  9:55     ` Arnd Bergmann
2021-04-14  6:45     ` Stephen Rothwell
2021-04-14  6:45       ` Stephen Rothwell
2021-04-14  6:45       ` Stephen Rothwell
2021-04-12  8:55 ` [PATCH 2/5] uapi: simplify __ARCH_FLOCK{,64}_PAD a little Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55 ` [PATCH 3/5] uapi: merge the 32-bit mips struct flock into the generic one Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55 ` [PATCH 4/5] uapi: always define F_GETLK64/F_SETLK64/F_SETLKW64 in fcntl.h Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-13 15:43   ` Helge Deller
2021-04-13 15:46     ` Christoph Hellwig
2021-04-13 15:58       ` Helge Deller
2021-04-12  8:55 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  8:55   ` Christoph Hellwig
2021-04-12  9:37   ` David Laight
2021-04-12  9:37     ` David Laight
2021-04-12  9:37     ` David Laight
2021-04-12 10:53     ` David Laight [this message]
2021-04-12 10:53       ` David Laight
2021-04-12 10:53       ` David Laight
2021-04-12 11:26       ` Arnd Bergmann
2021-04-12 11:26         ` Arnd Bergmann
2021-04-12 11:26         ` Arnd Bergmann
2021-04-12 13:11         ` David Laight
2021-04-12 13:11           ` David Laight
2021-04-12 13:11           ` David Laight
2021-04-12 10:03 ` consolidate the flock uapi definitions Arnd Bergmann
2021-04-12 10:03   ` Arnd Bergmann
2021-04-12 10:03   ` Arnd Bergmann
2021-04-12 10:22   ` David Laight
2021-04-12 10:22     ` David Laight
2021-04-12 10:22     ` David Laight
2021-04-12 11:07     ` Arnd Bergmann
2021-04-12 11:07       ` Arnd Bergmann
2021-04-12 11:07       ` Arnd Bergmann
2021-04-15 12:20 ` Heiko Carstens
2021-04-15 12:20   ` Heiko Carstens
2021-04-15 12:20   ` Heiko Carstens
2022-01-11  8:35 consolidate the compat fcntl definitions Christoph Hellwig
2022-01-11  8:35 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
2022-01-11  8:35   ` Christoph Hellwig
2022-01-11  8:35   ` Christoph Hellwig
2022-01-11  9:52   ` David Laight
2022-01-11  9:52     ` David Laight
2022-01-11  9:52     ` David Laight
2022-01-31  6:49 consolidate the compat fcntl definitions v2 Christoph Hellwig
2022-01-31  6:49 ` [PATCH 5/5] compat: consolidate the compat_flock{,64} definition Christoph Hellwig
2022-01-31  6:49   ` Christoph Hellwig
2022-01-31  6:49   ` Christoph Hellwig

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