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Date:      Wed, 1 Apr 2015 08:25:41 +0000 (UTC)
From:      Konstantin Belousov <kib@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r280949 - head/sys/fs/devfs
Message-ID:  <201504010825.t318PfCB038332@svn.freebsd.org>
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Author: kib
Date: Wed Apr  1 08:25:40 2015
New Revision: 280949
URL: https://svnweb.freebsd.org/changeset/base/280949

Log:
  Refine r280308.  Do not completely disable timestamping of devfs nodes
  on reads or writes, the time marks are used to display idle time by
  w(1) [1].  Instead, use vfs.devfs.dotimes as the selector of default
  precision vs. using time_second.  The later gives seconds precision,
  which is good enough for the purpose.
  
  Note that timestamp updates are unlocked and the updates itself, as
  well as the check in devfs_timestamp, are non-atomic.
  
  Noted by:	truckman [1]
  Reviewed by:	bde
  Sponsored by:	The FreeBSD Foundation
  MFC after:	1 week

Modified:
  head/sys/fs/devfs/devfs_vnops.c

Modified: head/sys/fs/devfs/devfs_vnops.c
==============================================================================
--- head/sys/fs/devfs/devfs_vnops.c	Wed Apr  1 06:44:39 2015	(r280948)
+++ head/sys/fs/devfs/devfs_vnops.c	Wed Apr  1 08:25:40 2015	(r280949)
@@ -84,7 +84,27 @@ SYSCTL_DECL(_vfs_devfs);
 
 static int devfs_dotimes;
 SYSCTL_INT(_vfs_devfs, OID_AUTO, dotimes, CTLFLAG_RW,
-        &devfs_dotimes, 0, "Update timestamps on DEVFS");
+    &devfs_dotimes, 0, "Update timestamps on DEVFS with default precision");
+
+/*
+ * Update devfs node timestamp.  Note that updates are unlocked and
+ * stat(2) could see partially updated times.
+ */
+static void
+devfs_timestamp(struct timespec *tsp)
+{
+	time_t ts;
+
+	if (devfs_dotimes) {
+		vfs_timestamp(tsp);
+	} else {
+		ts = time_second;
+		if (tsp->tv_sec != ts) {
+			tsp->tv_sec = ts;
+			tsp->tv_nsec = 0;
+		}
+	}
+}
 
 static int
 devfs_fp_check(struct file *fp, struct cdev **devp, struct cdevsw **dswp,
@@ -1228,9 +1248,8 @@ devfs_read_f(struct file *fp, struct uio
 
 	foffset_lock_uio(fp, uio, flags | FOF_NOLOCK);
 	error = dsw->d_read(dev, uio, ioflag);
-	if (devfs_dotimes &&
-	    (uio->uio_resid != resid || (error == 0 && resid != 0)))
-		vfs_timestamp(&dev->si_atime);
+	if (uio->uio_resid != resid || (error == 0 && resid != 0))
+		devfs_timestamp(&dev->si_atime);
 	td->td_fpop = fpop;
 	dev_relthread(dev, ref);
 
@@ -1708,9 +1727,8 @@ devfs_write_f(struct file *fp, struct ui
 	resid = uio->uio_resid;
 
 	error = dsw->d_write(dev, uio, ioflag);
-	if (devfs_dotimes &&
-	    (uio->uio_resid != resid || (error == 0 && resid != 0))) {
-		vfs_timestamp(&dev->si_ctime);
+	if (uio->uio_resid != resid || (error == 0 && resid != 0)) {
+		devfs_timestamp(&dev->si_ctime);
 		dev->si_mtime = dev->si_ctime;
 	}
 	td->td_fpop = fpop;

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