Commit 2c7387ef authored by Chris Metcalf's avatar Chris Metcalf

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: default avatarChris Metcalf <cmetcalf@tilera.com>
Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
parent 1deb9c5d
#ifdef CONFIG_COMPAT
#define __ARCH_WANT_STAT64 /* Used for compat_sys_stat64() etc. */
#endif
#include <asm-generic/stat.h> #include <asm-generic/stat.h>
...@@ -41,6 +41,7 @@ __SYSCALL(__NR_cmpxchg_badaddr, sys_cmpxchg_badaddr) ...@@ -41,6 +41,7 @@ __SYSCALL(__NR_cmpxchg_badaddr, sys_cmpxchg_badaddr)
#ifdef CONFIG_COMPAT #ifdef CONFIG_COMPAT
#define __ARCH_WANT_SYS_LLSEEK #define __ARCH_WANT_SYS_LLSEEK
#endif #endif
#define __ARCH_WANT_SYS_NEWFSTATAT
#endif #endif
#endif /* _ASM_TILE_UNISTD_H */ #endif /* _ASM_TILE_UNISTD_H */
...@@ -148,11 +148,11 @@ long tile_compat_sys_msgrcv(int msqid, ...@@ -148,11 +148,11 @@ long tile_compat_sys_msgrcv(int msqid,
#define compat_sys_readahead sys32_readahead #define compat_sys_readahead sys32_readahead
#define compat_sys_sync_file_range compat_sys_sync_file_range2 #define compat_sys_sync_file_range compat_sys_sync_file_range2
/* The native 64-bit "struct stat" matches the 32-bit "struct stat64". */ /* We leverage the "struct stat64" type for 32-bit time_t/nsec. */
#define compat_sys_stat64 sys_newstat #define compat_sys_stat64 sys_stat64
#define compat_sys_lstat64 sys_newlstat #define compat_sys_lstat64 sys_lstat64
#define compat_sys_fstat64 sys_newfstat #define compat_sys_fstat64 sys_fstat64
#define compat_sys_fstatat64 sys_newfstatat #define compat_sys_fstatat64 sys_fstatat64
/* The native sys_ptrace dynamically handles compat binaries. */ /* The native sys_ptrace dynamically handles compat binaries. */
#define compat_sys_ptrace sys_ptrace #define compat_sys_ptrace sys_ptrace
......
...@@ -33,18 +33,18 @@ struct stat { ...@@ -33,18 +33,18 @@ struct stat {
int st_blksize; /* Optimal block size for I/O. */ int st_blksize; /* Optimal block size for I/O. */
int __pad2; int __pad2;
long st_blocks; /* Number 512-byte blocks allocated. */ long st_blocks; /* Number 512-byte blocks allocated. */
int st_atime; /* Time of last access. */ long st_atime; /* Time of last access. */
unsigned int st_atime_nsec; unsigned long st_atime_nsec;
int st_mtime; /* Time of last modification. */ long st_mtime; /* Time of last modification. */
unsigned int st_mtime_nsec; unsigned long st_mtime_nsec;
int st_ctime; /* Time of last status change. */ long st_ctime; /* Time of last status change. */
unsigned int st_ctime_nsec; unsigned long st_ctime_nsec;
unsigned int __unused4; unsigned int __unused4;
unsigned int __unused5; unsigned int __unused5;
}; };
#if __BITS_PER_LONG != 64
/* This matches struct stat64 in glibc2.1. Only used for 32 bit. */ /* This matches struct stat64 in glibc2.1. Only used for 32 bit. */
#if __BITS_PER_LONG != 64 || defined(__ARCH_WANT_STAT64)
struct stat64 { struct stat64 {
unsigned long long st_dev; /* Device. */ unsigned long long st_dev; /* Device. */
unsigned long long st_ino; /* File serial number. */ unsigned long long st_ino; /* File serial number. */
......
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