Commit 1741937d authored by Dmitry V. Levin's avatar Dmitry V. Levin Committed by Al Viro

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: a528d35e ("statx: Add a system call to make enhanced file info available")
Signed-off-by: default avatarDmitry V. Levin <ldv@altlinux.org>
Signed-off-by: default avatarDavid Howells <dhowells@redhat.com>
cc: linux-api@vger.kernel.org
cc: mtk.manpages@gmail.com
Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent 85128b2b
......@@ -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;
};
......
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