diff options
author | Dmitry V. Levin <ldv@altlinux.org> | 2017-04-26 14:50:00 +0100 |
---|---|---|
committer | Al Viro <viro@zeniv.linux.org.uk> | 2017-04-26 21:19:05 -0400 |
commit | 1741937d475d91ed95abb37f07e8571e23b9a7fe (patch) | |
tree | aed1220a5aa1c62bcf2f18c0d8c22bc26a8c376d | |
parent | 85128b2be6738fe36c224995c5ee80fe80fbb1b5 (diff) | |
download | lwn-1741937d475d91ed95abb37f07e8571e23b9a7fe.tar.gz lwn-1741937d475d91ed95abb37f07e8571e23b9a7fe.zip |
uapi: change the type of struct statx_timestamp.tv_nsec to unsigned
The comment asserting that the value of struct statx_timestamp.tv_nsec
must be negative when statx_timestamp.tv_sec is negative, is wrong, as
could be seen from the following example:
#define _FILE_OFFSET_BITS 64
#include <assert.h>
#include <fcntl.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <asm/unistd.h>
#include <linux/stat.h>
int main(void)
{
static const struct timespec ts[2] = {
{ .tv_nsec = UTIME_OMIT },
{ .tv_sec = -2, .tv_nsec = 42 }
};
assert(utimensat(AT_FDCWD, ".", ts, 0) == 0);
struct stat st;
assert(stat(".", &st) == 0);
printf("st_mtim.tv_sec = %lld, st_mtim.tv_nsec = %lu\n",
(long long) st.st_mtim.tv_sec,
(unsigned long) st.st_mtim.tv_nsec);
struct statx stx;
assert(syscall(__NR_statx, AT_FDCWD, ".", 0, 0, &stx) == 0);
printf("stx_mtime.tv_sec = %lld, stx_mtime.tv_nsec = %lu\n",
(long long) stx.stx_mtime.tv_sec,
(unsigned long) stx.stx_mtime.tv_nsec);
return 0;
}
It expectedly prints:
st_mtim.tv_sec = -2, st_mtim.tv_nsec = 42
stx_mtime.tv_sec = -2, stx_mtime.tv_nsec = 42
The more generic comment asserting that the value of struct
statx_timestamp.tv_nsec might be negative is confusing to say the least.
It contradicts both the struct stat.st_[acm]time_nsec tradition and
struct timespec.tv_nsec requirements in utimensat syscall.
If statx syscall ever returns a stx_[acm]time containing a negative
tv_nsec that cannot be passed unmodified to utimensat syscall,
it will cause an immense confusion.
Fix this source of confusion by changing the type of struct
statx_timestamp.tv_nsec from __s32 to __u32.
Fixes: a528d35e8bfc ("statx: Add a system call to make enhanced file info available")
Signed-off-by: Dmitry V. Levin <ldv@altlinux.org>
Signed-off-by: David Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
cc: mtk.manpages@gmail.com
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
-rw-r--r-- | include/uapi/linux/stat.h | 8 |
1 files changed, 2 insertions, 6 deletions
diff --git a/include/uapi/linux/stat.h b/include/uapi/linux/stat.h index d538897b8e08..17b10304c393 100644 --- a/include/uapi/linux/stat.h +++ b/include/uapi/linux/stat.h @@ -48,17 +48,13 @@ * tv_sec holds the number of seconds before (negative) or after (positive) * 00:00:00 1st January 1970 UTC. * - * tv_nsec holds a number of nanoseconds before (0..-999,999,999 if tv_sec is - * negative) or after (0..999,999,999 if tv_sec is positive) the tv_sec time. - * - * Note that if both tv_sec and tv_nsec are non-zero, then the two values must - * either be both positive or both negative. + * tv_nsec holds a number of nanoseconds (0..999,999,999) after the tv_sec time. * * __reserved is held in case we need a yet finer resolution. */ struct statx_timestamp { __s64 tv_sec; - __s32 tv_nsec; + __u32 tv_nsec; __s32 __reserved; }; |