[src/trunk]: src/sys introduce vfs.generic.timestamp_precision sysctl to cont...

[jdolecek <jdolecek%NetBSD.org@localhost>]

details:   https://anonhg.NetBSD.org/src/rev/b807f5ee42d9
branches:  trunk
changeset: 951508:b807f5ee42d9
user:      jdolecek <jdolecek%NetBSD.org@localhost>
date:      Thu Feb 04 21:07:06 2021 +0000

description:
introduce vfs.generic.timestamp_precision sysctl to control precision
of the timer used for vfs_timestamp(); default stays the same
to use nanotime(9), but option is there to use the faster, albeit
less precise methods

code taken from FreeBSD

suggested by Mateusz Guzik in:
http://mail-index.netbsd.org/tech-kern/2020/07/19/msg026620.html

diffstat:

 sys/kern/vfs_init.c |  12 ++++++++++--
 sys/kern/vfs_subr.c |  37 +++++++++++++++++++++++++++++++++----
 sys/sys/mount.h     |   3 ++-
 3 files changed, 45 insertions(+), 7 deletions(-)

diffs (118 lines):

diff -r 0f4a5ba419cf -r b807f5ee42d9 sys/kern/vfs_init.c
--- a/sys/kern/vfs_init.c       Thu Feb 04 20:19:09 2021 +0000
+++ b/sys/kern/vfs_init.c       Thu Feb 04 21:07:06 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_init.c,v 1.51 2020/05/16 18:31:50 christos Exp $   */
+/*     $NetBSD: vfs_init.c,v 1.52 2021/02/04 21:07:06 jdolecek Exp $   */
 
 /*-
  * Copyright (c) 1998, 2000, 2008 The NetBSD Foundation, Inc.
@@ -67,7 +67,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_init.c,v 1.51 2020/05/16 18:31:50 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_init.c,v 1.52 2021/02/04 21:07:06 jdolecek Exp $");
 
 #include <sys/param.h>
 #include <sys/mount.h>
@@ -151,6 +151,7 @@
 sysctl_vfs_setup(void)
 {
        extern int vfs_magiclinks;
+       extern int vfs_timestamp_precision;
 
        sysctl_createv(&vfs_sysctllog, 0, NULL, NULL,
                       CTLFLAG_PERMANENT,
@@ -170,6 +171,13 @@
                       SYSCTL_DESCR("Whether \"magic\" symlinks are expanded"),
                       NULL, 0, &vfs_magiclinks, 0,
                       CTL_VFS, VFS_GENERIC, VFS_MAGICLINKS, CTL_EOL);
+       sysctl_createv(&vfs_sysctllog, 0, NULL, NULL,
+                       CTLFLAG_PERMANENT|CTLFLAG_READWRITE,
+                       CTLTYPE_INT, "timestamp_precision",
+                       SYSCTL_DESCR("File timestamp precision"),
+                       NULL, 0, &vfs_timestamp_precision, 0,
+                       CTL_VFS, VFS_GENERIC, VFS_TIMESTAMP_PRECISION,
+                       CTL_EOL);
 }
 
 
diff -r 0f4a5ba419cf -r b807f5ee42d9 sys/kern/vfs_subr.c
--- a/sys/kern/vfs_subr.c       Thu Feb 04 20:19:09 2021 +0000
+++ b/sys/kern/vfs_subr.c       Thu Feb 04 21:07:06 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: vfs_subr.c,v 1.489 2020/07/26 21:28:33 christos Exp $  */
+/*     $NetBSD: vfs_subr.c,v 1.490 2021/02/04 21:07:06 jdolecek Exp $  */
 
 /*-
  * Copyright (c) 1997, 1998, 2004, 2005, 2007, 2008, 2019, 2020
@@ -69,7 +69,7 @@
  */
 
 #include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.489 2020/07/26 21:28:33 christos Exp $");
+__KERNEL_RCSID(0, "$NetBSD: vfs_subr.c,v 1.490 2021/02/04 21:07:06 jdolecek Exp $");
 
 #ifdef _KERNEL_OPT
 #include "opt_ddb.h"
@@ -1253,11 +1253,40 @@
        return 0;
 }
 
+/*
+ * Knob to control the precision of file timestamps:
+ *
+ *   0 = seconds only; nanoseconds zeroed.
+ *   1 = seconds and nanoseconds, accurate within 1/HZ.
+ *   2 = seconds and nanoseconds, truncated to microseconds.
+ * >=3 = seconds and nanoseconds, maximum precision.
+ */
+enum { TSP_SEC, TSP_HZ, TSP_USEC, TSP_NSEC };
+
+int vfs_timestamp_precision __read_mostly = TSP_NSEC;
+
 void
-vfs_timestamp(struct timespec *ts)
+vfs_timestamp(struct timespec *tsp)
 {
+       struct timeval tv;
 
-       nanotime(ts);
+       switch (vfs_timestamp_precision) {
+       case TSP_SEC:
+               tsp->tv_sec = time_second;
+               tsp->tv_nsec = 0;
+               break;
+       case TSP_HZ:
+               getnanotime(tsp);
+               break;
+       case TSP_USEC:
+               microtime(&tv);
+               TIMEVAL_TO_TIMESPEC(&tv, tsp);
+               break;
+       case TSP_NSEC:
+       default:
+               nanotime(tsp);
+               break;
+       }
 }
 
 /*
diff -r 0f4a5ba419cf -r b807f5ee42d9 sys/sys/mount.h
--- a/sys/sys/mount.h   Thu Feb 04 20:19:09 2021 +0000
+++ b/sys/sys/mount.h   Thu Feb 04 21:07:06 2021 +0000
@@ -1,4 +1,4 @@
-/*     $NetBSD: mount.h,v 1.236 2020/01/17 20:08:10 ad Exp $   */
+/*     $NetBSD: mount.h,v 1.237 2021/02/04 21:07:06 jdolecek Exp $     */
 
 /*
  * Copyright (c) 1989, 1991, 1993
@@ -115,6 +115,7 @@
                                           as next argument */
 #define VFS_USERMOUNT  3               /* enable/disable fs mnt by non-root */
 #define        VFS_MAGICLINKS  4               /* expand 'magic' symlinks */
+#define        VFS_TIMESTAMP_PRECISION  5      /* file timestamp precision */
 
 /* vfsquery flags for kqueue(2) */
 #define VQ_MOUNT       0x0001  /* new filesystem arrived */