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From: David Laight <David.Laight@ACULAB.COM>
To: 'Arnd Bergmann' <arnd@arndb.de>, Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@lst.de>,
	Andrew Morton <akpm@linux-foundation.org>,
	Jens Axboe <axboe@kernel.dk>, David Howells <dhowells@redhat.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" <io-uring@vger.kernel.org>,
	linux-arch <linux-arch@vger.kernel.org>,
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	Networking <netdev@vger.kernel.org>,
	"keyrings@vger.kernel.org" <keyrings@vger.kernel.org>,
	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 21:30:25 +0000
Message-ID: <2e11ea867c644c5d96f8e4930e5c730d@AcuMS.aculab.com> (raw)
In-Reply-To: <CAK8P3a3nkLUOkR+jwz2_2LcYTUTqdVf8JOtZqKWbtEDotNhFZA@mail.gmail.com>

From: Arnd Bergmann
> Sent: 23 September 2020 19:46
...
> 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.

A similar 'trick' (that probably won't work here) is to pass
the name of a #define function as a parameter to another define.
Useful for defining constants and error strings together. eg:
#define TRAFFIC_LIGHTS(x) \
	x(RED, 0, "Red") \
	x(YELLOW, 1, "Yellow) \
	x(GREEN, 2, "GREEN)

You can then do thing like:
#define x(token, value, string) token = value,
enum {TRAFFIC_LIGHTS(x) NUM_LIGHTS};
#undef x
#define x(token, value, string) [value] = string,
const char *colours[] = {TRAFFIC_LIGHTS(x)};
#undef x
to initialise constants and a name table that are always in sync.

It is also a good way to generate source lines that are over 1MB.

	David

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

  parent 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
2020-09-23 19:52               ` Arnd Bergmann
2020-09-23 21:30             ` David Laight [this message]
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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