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From: Al Viro <viro@zeniv.linux.org.uk>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, David Howells <dhowells@redhat.com>,
	David Laight <David.Laight@aculab.com>,
	Linux ARM <linux-arm-kernel@lists.infradead.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"open list:BROADCOM NVRAM DRIVER" <linux-mips@vger.kernel.org>,
	Parisc List <linux-parisc@vger.kernel.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
	linux-s390 <linux-s390@vger.kernel.org>,
	sparclinux <sparclinux@vger.kernel.org>,
	linux-block <linux-block@vger.kernel.org>,
	linux-scsi <linux-scsi@vger.kernel.org>,
	Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
	linux-aio <linux-aio@kvack.org>,
	io-uring@vger.kernel.org, linux-arch <linux-arch@vger.kernel.org>,
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	Networking <netdev@vger.kernel.org>,
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	LSM List <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH 5/9] fs: remove various compat readv/writev helpers
Date: Wed, 23 Sep 2020 20:47:55 +0100
Message-ID: <20200923194755.GR3421308@ZenIV.linux.org.uk> (raw)
In-Reply-To: <CAK8P3a3nkLUOkR+jwz2_2LcYTUTqdVf8JOtZqKWbtEDotNhFZA@mail.gmail.com>

On Wed, Sep 23, 2020 at 08:45:51PM +0200, Arnd Bergmann wrote:
> On Wed, Sep 23, 2020 at 6:38 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
> >
> > I wonder if we should do something like
> >
> > SYSCALL_DECLARE3(readv, unsigned long, fd, const struct iovec __user *, vec,
> >                  unsigned long, vlen);
> > in syscalls.h instead, and not under that ifdef.
> >
> > Let it expand to declaration of sys_...() in generic case and, on x86, into
> > __do_sys_...() and __ia32_sys_...()/__x64_sys_...(), with types matching
> > what SYSCALL_DEFINE ends up using.
> >
> > Similar macro would cover compat_sys_...() declarations.  That would
> > restore mismatch checking for x86 and friends.  AFAICS, the cost wouldn't
> > be terribly high - cpp would have more to chew through in syscalls.h,
> > but it shouldn't be all that costly.  Famous last words, of course...
> >
> > Does anybody see fundamental problems with that?
> 
> I've had some ideas along those lines in the past and I think it should work.
> 
> As a variation of this, the SYSCALL_DEFINEx() macros could go away
> entirely, leaving only the macro instantiations from the header to
> require that syntax. It would require first changing the remaining
> architectures to build the syscall table from C code instead of
> assembler though.
> 
> Regardless of that, another advantage of having the SYSCALL_DECLAREx()
> would be the ability to include that header file from elsewhere with a different
> macro definition to create a machine-readable version of the interface when
> combined with the syscall.tbl files. This could be used to create a user
> space stub for calling into the low-level syscall regardless of the
> libc interfaces,
> or for synchronizing the interfaces with strace, qemu-user, or anything that
> needs to deal with the low-level interface.

FWIW, after playing with that for a while...  Do we really want the
compat_sys_...() declarations to live in linux/compat.h?  Most of
the users of that file don't want those; why not move them to
linux/syscalls.h?

Reason: there's a lot more users of linux/compat.h than those of
linux/syscalls.h - it's pulled by everything in the networking stack,
for starters...

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-09-23  6:05 let import_iovec deal with compat_iovecs as well v3 Christoph Hellwig
2020-09-23  6:05 ` [PATCH 1/9] compat.h: fix a spelling error in <linux/compat.h> Christoph Hellwig
2020-09-23  6:05 ` [PATCH 2/9] iov_iter: move rw_copy_check_uvector() into lib/iov_iter.c Christoph Hellwig
2020-09-23  6:05 ` [PATCH 3/9] iov_iter: refactor rw_copy_check_uvector and import_iovec Christoph Hellwig
2020-09-23 14:16   ` Al Viro
2020-09-23 14:38     ` David Laight
2020-09-23 14:49       ` Al Viro
2020-09-23 14:40     ` Al Viro
2020-09-23  6:05 ` [PATCH 4/9] iov_iter: transparently handle compat iovecs in import_iovec Christoph Hellwig
2020-09-23  6:05 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-23 14:25   ` Al Viro
2020-09-23 14:32     ` Christoph Hellwig
2020-09-23 14:59       ` Al Viro
2020-09-23 16:38         ` Al Viro
2020-09-23 17:05           ` Al Viro
2020-09-23 17:46             ` Christoph Hellwig
2020-09-23 17:08           ` Brian Gerst
2020-09-23 18:45           ` Arnd Bergmann
2020-09-23 19:47             ` Al Viro [this message]
2020-09-23 19:52               ` Arnd Bergmann
2020-09-23 21:30             ` David Laight
2020-09-23  6:05 ` [PATCH 6/9] fs: remove the compat readv/writev syscalls Christoph Hellwig
2020-09-23  6:05 ` [PATCH 7/9] fs: remove compat_sys_vmsplice Christoph Hellwig
2020-09-23  6:05 ` [PATCH 8/9] mm: remove compat_process_vm_{readv,writev} Christoph Hellwig
2020-09-23  6:05 ` [PATCH 9/9] security/keys: remove compat_keyctl_instantiate_key_iov Christoph Hellwig
  -- strict thread matches above, loose matches on Subject: below --
2020-09-25  4:51 let import_iovec deal with compat_iovecs as well v4 Christoph Hellwig
2020-09-25  4:51 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig
2020-09-18 12:45 let import_iovec deal with compat_iovecs as well Christoph Hellwig
2020-09-18 12:45 ` [PATCH 5/9] fs: remove various compat readv/writev helpers Christoph Hellwig

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