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.

DVDmitry V. Levin committed 9 years ago