linux/arch/tile/include/asm/unistd.h
Chris Metcalf 2c7387ef99 asm-generic/stat.h: support 64-bit file time_t for stat()
The existing asm-generic/stat.h specifies st_mtime, etc., as a 32-value,
and works well for 32-bit architectures (currently microblaze, score,
and 32-bit tile).  However, for 64-bit architectures it isn't sufficient
to return 32 bits of time_t; this isn't good insurance against the 2037
rollover.  (It also makes glibc support less convenient, since we can't
use glibc's handy STAT_IS_KERNEL_STAT mode.)

This change extends the two "timespec" fields for each of the three atime,
mtime, and ctime fields from "int" to "long".  As a result, on 32-bit
platforms nothing changes, and 64-bit platforms will now work as expected.

The only wrinkle is 32-bit userspace under 64-bit kernels taking advantage
of COMPAT mode.  For these, we leave the "struct stat64" definitions with
the "int" versions of the time_t and nsec fields, so that architectures
can implement compat_sys_stat64() and friends with sys_stat64(), etc.,
and get the expected 32-bit structure layout.  This requires a
field-by-field copy in the kernel, implemented by the code guarded
under __ARCH_WANT_STAT64.

This does mean that the shape of the "struct stat" and "struct stat64"
structures is different on a 64-bit kernel, but only one of the two
structures should ever be used by any given process: "struct stat"
is meant for 64-bit userspace only, and "struct stat64" for 32-bit
userspace only.  (On a 32-bit kernel the two structures continue to have
the same shape, since "long" is 32 bits.)

The alternative is keeping the two structures the same shape on 64-bit
kernels, which means a 64-bit time_t in "struct stat64" for 32-bit
processes.  This is a little unnatural since 32-bit userspace can't
do anything with 64 bits of time_t information, since time_t is just
"long", not "int64_t"; and in any case 32-bit userspace might expect
to be running under a 32-bit kernel, which can't provide the high 32
bits anyway.  In the case of a 32-bit kernel we'd then be extending the
kernel's 32-bit time_t to 64 bits, then truncating it back to 32 bits
again in userspace, for no particular reason.  And, as mentioned above,
if we have 64-bit time_t for 32-bit processes we can't easily use glibc's
STAT_IS_KERNEL_STAT, since glibc's stat structure requires an embedded
"struct timespec", which is a pair of "long" (32-bit) values in a 32-bit
userspace.  "Inventive" solutions are possible, but are pretty hacky.

Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
2010-11-01 15:31:29 -04:00

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C

/*
* Copyright 2010 Tilera Corporation. All Rights Reserved.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation, version 2.
*
* This program is distributed in the hope that it will be useful, but
* WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
* NON INFRINGEMENT. See the GNU General Public License for
* more details.
*/
#if !defined(_ASM_TILE_UNISTD_H) || defined(__SYSCALL)
#define _ASM_TILE_UNISTD_H
#ifndef __LP64__
/* Use the flavor of this syscall that matches the 32-bit API better. */
#define __ARCH_WANT_SYNC_FILE_RANGE2
#endif
/* Use the standard ABI for syscalls. */
#include <asm-generic/unistd.h>
/* Additional Tilera-specific syscalls. */
#define __NR_flush_cache (__NR_arch_specific_syscall + 1)
__SYSCALL(__NR_flush_cache, sys_flush_cache)
#ifndef __tilegx__
/* "Fast" syscalls provide atomic support for 32-bit chips. */
#define __NR_FAST_cmpxchg -1
#define __NR_FAST_atomic_update -2
#define __NR_FAST_cmpxchg64 -3
#define __NR_cmpxchg_badaddr (__NR_arch_specific_syscall + 0)
__SYSCALL(__NR_cmpxchg_badaddr, sys_cmpxchg_badaddr)
#endif
#ifdef __KERNEL__
/* In compat mode, we use sys_llseek() for compat_sys_llseek(). */
#ifdef CONFIG_COMPAT
#define __ARCH_WANT_SYS_LLSEEK
#endif
#define __ARCH_WANT_SYS_NEWFSTATAT
#endif
#endif /* _ASM_TILE_UNISTD_H */