vcs: hook sysfs devices into object lifetime instead of "binding"

During bootup performance tracing I noticed many occurrences of
vca* device creation and removal, leading to the usual userspace
uevent processing, which are, in this case, rather pointless.

A simple test showing the kernel timing (not including all the
work userspace has to do), gives us these numbers:
  $ time for i in `seq 1000`; do echo a > /dev/tty2; done
  real    0m1.142s
  user    0m0.015s
  sys     0m0.540s

If we move the hook for the vcs* driver core devices from the
tty "binding" to the vc allocation/deallocation, which is what
the vcs* devices represent, we get the following numbers:
  $ time for i in `seq 1000`; do echo a > /dev/tty2; done
  real    0m0.152s
  user    0m0.030s
  sys     0m0.072s

Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 8 insertions, 8 deletions

diff --git a/drivers/char/vc_screen.c b/drivers/char/vc_screen.c
index 4f3b3f95fc42..d94d25c12aa8 100644
--- a/drivers/char/vc_screen.c
+++ b/drivers/char/vc_screen.c
@@ -479,18 +479,18 @@ static const struct file_operations vcs_fops = {
 
 static struct class *vc_class;
 
-void vcs_make_sysfs(struct tty_struct *tty)
+void vcs_make_sysfs(int index)
 {
-        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 1), NULL,
-                      "vcs%u", tty->index + 1);
-        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, tty->index + 129), NULL,
-                      "vcsa%u", tty->index + 1);
+        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 1), NULL,
+                      "vcs%u", index + 1);
+        device_create(vc_class, NULL, MKDEV(VCS_MAJOR, index + 129), NULL,
+                      "vcsa%u", index + 1);
 }
 
-void vcs_remove_sysfs(struct tty_struct *tty)
+void vcs_remove_sysfs(int index)
 {
-        device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 1));
-        device_destroy(vc_class, MKDEV(VCS_MAJOR, tty->index + 129));
+        device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 1));
+        device_destroy(vc_class, MKDEV(VCS_MAJOR, index + 129));
 }
 
 int __init vcs_init(void)