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author | Chris Metcalf <cmetcalf@tilera.com> | 2010-10-29 00:07:07 +0400 |
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committer | Chris Metcalf <cmetcalf@tilera.com> | 2010-11-01 22:31:29 +0300 |
commit | 2c7387ef9969bb073c25ecbdcc5be30770267b16 (patch) | |
tree | 21025658ae17a84b0df346b589eb6c986c6f599d /include/asm-generic | |
parent | 1deb9c5dfb179819ecdbf80a1d121e26c63caab3 (diff) | |
download | linux-2c7387ef9969bb073c25ecbdcc5be30770267b16.tar.xz |
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 'include/asm-generic')
-rw-r--r-- | include/asm-generic/stat.h | 14 |
1 files changed, 7 insertions, 7 deletions
diff --git a/include/asm-generic/stat.h b/include/asm-generic/stat.h index 47e64170305d..bd8cad21998e 100644 --- a/include/asm-generic/stat.h +++ b/include/asm-generic/stat.h @@ -33,18 +33,18 @@ struct stat { int st_blksize; /* Optimal block size for I/O. */ int __pad2; long st_blocks; /* Number 512-byte blocks allocated. */ - int st_atime; /* Time of last access. */ - unsigned int st_atime_nsec; - int st_mtime; /* Time of last modification. */ - unsigned int st_mtime_nsec; - int st_ctime; /* Time of last status change. */ - unsigned int st_ctime_nsec; + long st_atime; /* Time of last access. */ + unsigned long st_atime_nsec; + long st_mtime; /* Time of last modification. */ + unsigned long st_mtime_nsec; + long st_ctime; /* Time of last status change. */ + unsigned long st_ctime_nsec; unsigned int __unused4; unsigned int __unused5; }; -#if __BITS_PER_LONG != 64 /* This matches struct stat64 in glibc2.1. Only used for 32 bit. */ +#if __BITS_PER_LONG != 64 || defined(__ARCH_WANT_STAT64) struct stat64 { unsigned long long st_dev; /* Device. */ unsigned long long st_ino; /* File serial number. */ |