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author | Chris Metcalf <cmetcalf@tilera.com> | 2010-10-28 16:07:07 -0400 |
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committer | Chris Metcalf <cmetcalf@tilera.com> | 2010-11-01 15:31:29 -0400 |
commit | 2c7387ef9969bb073c25ecbdcc5be30770267b16 (patch) | |
tree | 21025658ae17a84b0df346b589eb6c986c6f599d /arch | |
parent | 1deb9c5dfb179819ecdbf80a1d121e26c63caab3 (diff) | |
download | linux-2c7387ef9969bb073c25ecbdcc5be30770267b16.tar.gz linux-2c7387ef9969bb073c25ecbdcc5be30770267b16.tar.bz2 linux-2c7387ef9969bb073c25ecbdcc5be30770267b16.zip |
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>
Diffstat (limited to 'arch')
-rw-r--r-- | arch/tile/include/asm/stat.h | 3 | ||||
-rw-r--r-- | arch/tile/include/asm/unistd.h | 1 | ||||
-rw-r--r-- | arch/tile/kernel/compat.c | 10 |
3 files changed, 9 insertions, 5 deletions
diff --git a/arch/tile/include/asm/stat.h b/arch/tile/include/asm/stat.h index 3dc90fa92c70..b16e5db8f0e7 100644 --- a/arch/tile/include/asm/stat.h +++ b/arch/tile/include/asm/stat.h @@ -1 +1,4 @@ +#ifdef CONFIG_COMPAT +#define __ARCH_WANT_STAT64 /* Used for compat_sys_stat64() etc. */ +#endif #include <asm-generic/stat.h> diff --git a/arch/tile/include/asm/unistd.h b/arch/tile/include/asm/unistd.h index f2e3ff485333..b35c2db71199 100644 --- a/arch/tile/include/asm/unistd.h +++ b/arch/tile/include/asm/unistd.h @@ -41,6 +41,7 @@ __SYSCALL(__NR_cmpxchg_badaddr, sys_cmpxchg_badaddr) #ifdef CONFIG_COMPAT #define __ARCH_WANT_SYS_LLSEEK #endif +#define __ARCH_WANT_SYS_NEWFSTATAT #endif #endif /* _ASM_TILE_UNISTD_H */ diff --git a/arch/tile/kernel/compat.c b/arch/tile/kernel/compat.c index 77739cdd9462..67617a05e602 100644 --- a/arch/tile/kernel/compat.c +++ b/arch/tile/kernel/compat.c @@ -148,11 +148,11 @@ long tile_compat_sys_msgrcv(int msqid, #define compat_sys_readahead sys32_readahead #define compat_sys_sync_file_range compat_sys_sync_file_range2 -/* The native 64-bit "struct stat" matches the 32-bit "struct stat64". */ -#define compat_sys_stat64 sys_newstat -#define compat_sys_lstat64 sys_newlstat -#define compat_sys_fstat64 sys_newfstat -#define compat_sys_fstatat64 sys_newfstatat +/* We leverage the "struct stat64" type for 32-bit time_t/nsec. */ +#define compat_sys_stat64 sys_stat64 +#define compat_sys_lstat64 sys_lstat64 +#define compat_sys_fstat64 sys_fstat64 +#define compat_sys_fstatat64 sys_fstatat64 /* The native sys_ptrace dynamically handles compat binaries. */ #define compat_sys_ptrace sys_ptrace |