MFC r280308 (by delphij):

Disable timestamping on devfs read/write operations by default.

MFC r280949:
Refine r280308.  Use seconds precision for devfs timestamps by default.

2 files changed, 30 insertions, 3 deletions

diff --git a/sys/fs/devfs/devfs_devs.c b/sys/fs/devfs/devfs_devs.c
index c2d40d3..5070985 100644
--- a/sys/fs/devfs/devfs_devs.c
+++ b/sys/fs/devfs/devfs_devs.c
@@ -61,7 +61,7 @@ static MALLOC_DEFINE(M_DEVFS2, "DEVFS2", "DEVFS data 2");
 static MALLOC_DEFINE(M_DEVFS3, "DEVFS3", "DEVFS data 3");
 static MALLOC_DEFINE(M_CDEVP, "DEVFS1", "DEVFS cdev_priv storage");
 
-static SYSCTL_NODE(_vfs, OID_AUTO, devfs, CTLFLAG_RW, 0, "DEVFS filesystem");
+SYSCTL_NODE(_vfs, OID_AUTO, devfs, CTLFLAG_RW, 0, "DEVFS filesystem");
 
 static unsigned devfs_generation;
 SYSCTL_UINT(_vfs_devfs, OID_AUTO, generation, CTLFLAG_RD,
diff --git a/sys/fs/devfs/devfs_vnops.c b/sys/fs/devfs/devfs_vnops.c
index 134f8b0..7f20389 100644
--- a/sys/fs/devfs/devfs_vnops.c
+++ b/sys/fs/devfs/devfs_vnops.c
@@ -57,6 +57,7 @@
 #include <sys/proc.h>
 #include <sys/stat.h>
 #include <sys/sx.h>
+#include <sys/sysctl.h>
 #include <sys/time.h>
 #include <sys/ttycom.h>
 #include <sys/unistd.h>
@@ -79,6 +80,32 @@ SX_SYSINIT(clone_drain_lock, &clone_drain_lock, "clone events drain lock");
 struct mtx	cdevpriv_mtx;
 MTX_SYSINIT(cdevpriv_mtx, &cdevpriv_mtx, "cdevpriv lock", MTX_DEF);
 
+SYSCTL_DECL(_vfs_devfs);
+
+static int devfs_dotimes;
+SYSCTL_INT(_vfs_devfs, OID_AUTO, dotimes, CTLFLAG_RW,
+    &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,
     int *ref)
@@ -1200,7 +1227,7 @@ devfs_read_f(struct file *fp, struct uio *uio, struct ucred *cred,
 	foffset_lock_uio(fp, uio, flags | FOF_NOLOCK);
 	error = dsw->d_read(dev, uio, ioflag);
 	if (uio->uio_resid != resid || (error == 0 && resid != 0))
-		vfs_timestamp(&dev->si_atime);
+		devfs_timestamp(&dev->si_atime);
 	td->td_fpop = fpop;
 	dev_relthread(dev, ref);
 
@@ -1679,7 +1706,7 @@ devfs_write_f(struct file *fp, struct uio *uio, struct ucred *cred,
 
 	error = dsw->d_write(dev, uio, ioflag);
 	if (uio->uio_resid != resid || (error == 0 && resid != 0)) {
-		vfs_timestamp(&dev->si_ctime);
+		devfs_timestamp(&dev->si_ctime);
 		dev->si_mtime = dev->si_ctime;
 	}
 	td->td_fpop = fpop;