touch: switch to using utimensat() and futimens()

This patch changes the functions used to update timestamps in touch.

Before, utimes() and lutimes() were used, which had certain
disadvantages.
They are unable to handle nanosecond timestamps, and implementations of
certain features like -a and -m require running stat() in a loop.

Almost all implementations of utimes() and lutimes() are wrappers for
utimensat(), this is the case for glibc, ulibc and musl libc.

function                                             old     new   delta
__futimens_time64                                      -      24     +24
__lutimes_time64                                      80       -     -80
touch_main                                           539     456     -83
------------------------------------------------------------------------------
(add/remove: 2/2 grow/shrink: 0/1 up/down: 24/-163)          Total: -139 bytes

Signed-off-by: urmum-69 <urmum69@snopyta.org>
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>

1 files changed, 16 insertions, 41 deletions

diff --git a/coreutils/touch.c b/coreutils/touch.c
index 690517e66..8d3f8dbbe 100644
--- a/coreutils/touch.c
+++ b/coreutils/touch.c
@@ -25,7 +25,6 @@
 //config:       depends on TOUCH
 //config:       help
 //config:       Enable touch to have the -h option.
-//config:       This requires libc support for lutimes() function.
 //config:
 //config:config FEATURE_TOUCH_SUSV3
 //config:       bool "Add support for SUSV3 features (-a -d -m -t -r)"
@@ -97,8 +96,6 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
                 OPT_a = (1 << (4+ENABLE_FEATURE_TOUCH_NODEREF)) * ENABLE_FEATURE_TOUCH_SUSV3,
                 OPT_m = (1 << (5+ENABLE_FEATURE_TOUCH_NODEREF)) * ENABLE_FEATURE_TOUCH_SUSV3,
         };
-        /* NULL = use current time */
-        const struct timeval *newtime = NULL;
 #if ENABLE_LONG_OPTS
         static const char touch_longopts[] ALIGN1 =
                 /* name, has_arg, val */
@@ -112,12 +109,11 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
         char *reference_file = NULL;
         char *date_str = NULL;
         /* timebuf[0] is atime, timebuf[1] is mtime */
-        struct timeval timebuf[2];
-        timebuf[1].tv_usec = timebuf[0].tv_usec = 0;
+        struct timespec timebuf[2];
 #else
 # define reference_file NULL
 # define date_str       NULL
-# define timebuf        ((struct timeval*)NULL)
+# define timebuf        ((struct timespec*)NULL)
 #endif
 
         /* -d and -t both set time. In coreutils,
@@ -140,16 +136,15 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
                 bb_show_usage();
         }
 
+        timebuf[0].tv_nsec = timebuf[1].tv_nsec = UTIME_NOW;
+
         if (reference_file) {
                 struct stat stbuf;
                 xstat(reference_file, &stbuf);
                 timebuf[0].tv_sec = stbuf.st_atime;
                 timebuf[1].tv_sec = stbuf.st_mtime;
-                /* Can use .st_mtim.tv_nsec
-                 * (or is it .st_mtimensec?? see date.c)
-                 * to set microseconds too.
-                 */
-                newtime = timebuf;
+                timebuf[0].tv_nsec = stbuf.st_atim.tv_nsec;
+                timebuf[1].tv_nsec = stbuf.st_mtim.tv_nsec;
         }
 
         if (date_str) {
@@ -167,39 +162,19 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
                 t = validate_tm_time(date_str, &tm_time);
 
                 timebuf[1].tv_sec = timebuf[0].tv_sec = t;
-                newtime = timebuf;
+                timebuf[1].tv_nsec = timebuf[0].tv_nsec = 0;
         }
 
-        if ((opts & (OPT_a | OPT_m)) && !newtime) {
-                time(&timebuf[0].tv_sec);
-                timebuf[1].tv_sec = timebuf[0].tv_sec;
-                newtime = timebuf;
+        if (opts & OPT_a) {
+                timebuf[1].tv_nsec = UTIME_OMIT;
+        }
+        if (opts & OPT_m) {
+                timebuf[0].tv_nsec = UTIME_OMIT;
         }
 
         do {
-                int result;
-
-                if (opts & (OPT_a | OPT_m)) {
-                        /* Save original times */
-                        struct stat stbuf;
-                        if (stat(*argv, &stbuf) == 0) {
-                                /* As we must set both times, we lose original
-                                 * file time microseconds.
-                                 * Can use .st_mtim.tv_nsec
-                                 * (or is it .st_mtimensec?? see date.c)
-                                 * to set microseconds too.
-                                 * Also, utimensat(2) allows to omit one of the
-                                 * times to be set. But it is SUSv4.
-                                 */
-                                if (!(opts & OPT_a))
-                                        timebuf[0].tv_sec = stbuf.st_atime;
-                                if (!(opts & OPT_m))
-                                        timebuf[1].tv_sec = stbuf.st_mtime;
-                        }
-                }
-
-                result = (ENABLE_FEATURE_TOUCH_NODEREF && (opts & OPT_h) ? lutimes : utimes)(*argv, newtime);
-
+                int result = utimensat(AT_FDCWD, *argv, timebuf,
+                                (opts & OPT_h) ? AT_SYMLINK_NOFOLLOW : 0);
                 if (result != 0) {
                         if (errno == ENOENT) { /* no such file? */
                                 if (opts & OPT_c) {
@@ -209,9 +184,9 @@ int touch_main(int argc UNUSED_PARAM, char **argv)
                                 /* Try to create the file */
                                 fd = open(*argv, O_RDWR | O_CREAT, 0666);
                                 if (fd >= 0) {
-                                        xclose(fd);
                                         if (reference_file || date_str)
-                                                utimes(*argv, newtime);
+                                                futimens(fd, timebuf);
+                                        xclose(fd);
                                         continue;
                                 }
                         }