[PATCH 07/11] fblog: allow selecting fbs via sysfs and module-parameters

[David Herrmann <dh.herrmann@googlemail.com>]

fblog is mainly useful during boot, reboot, panics and maintenance. In all
cases you often want to control which monitors are used for console
output. Moreover, in multi-seat environments it is desireable to reduce
system-overhead by not drawing the console to all framebuffers. Four
mechanisms to select framebuffers for fblog are added:

1) "active" module parameter: This parameter selects whether fblog has
access to available framebuffer devices. If it is true, then fblog will
open devices following the rules described below and rendering will take
place. If it is false, new hotplugged devices will not be activated and no
more rendering to currently active devices takes place. However, active
devices will continue rendering after this is set to true again.

2) "active" sysfs attribute for each fblog object. Reading this value
returns whether a framebuffer is currently active. Writing it opens/closes
the framebuffer. This allows runtime control which fbs are used. For
instance, init can set these to 0 after bootup.
Note that a framebuffer is only active if this is 1 _and_ the "active"
module parameter is set to "true".

3) "activate_on_hotplug" module parameter: This selects whether a device
is activated by default when hotplugged. This is true by default so new
devices will be automatically activated.

4) "main_only" module parameter: This selects what devices are activated
on hotplug. This has no effect if "activate_on_hotplug" is false.
Otherwise, if this is true then only fb0 will be activated on hotplug.
This is false by default.

Signed-off-by: David Herrmann <dh.herrmann@googlemail.com>
---
 drivers/video/console/fblog.c | 66 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 65 insertions(+), 1 deletion(-)

diff --git a/drivers/video/console/fblog.c b/drivers/video/console/fblog.c
index 1c526c5..aed77dc 100644
--- a/drivers/video/console/fblog.c
+++ b/drivers/video/console/fblog.c
@@ -44,6 +44,9 @@ struct fblog_fb {
 
 static DEFINE_MUTEX(fblog_registration_lock);
 static struct fblog_fb *fblog_fbs[FB_MAX];
+static bool active = true;
+static bool activate_on_hotplug = true;
+static bool main_only = false;
 
 #define to_fblog_dev(_d) container_of(_d, struct fblog_fb, dev)
 
@@ -63,6 +66,9 @@ static int fblog_open(struct fblog_fb *fb)
 {
 	int ret;
 
+	if (!active)
+		return -EPERM;
+
 	mutex_lock(&fb->lock);
 
 	if (test_bit(FBLOG_KILLED, &fb->flags)) {
@@ -115,6 +121,40 @@ static void fblog_close(struct fblog_fb *fb, bool kill_dev)
 	mutex_unlock(&fb->lock);
 }
 
+static ssize_t fblog_dev_active_show(struct device *dev,
+				     struct device_attribute *attr,
+				     char *buf)
+{
+	struct fblog_fb *fb = to_fblog_dev(dev);
+
+	return snprintf(buf, PAGE_SIZE, "%d\n",
+			!!test_bit(FBLOG_OPEN, &fb->flags));
+}
+
+static ssize_t fblog_dev_active_store(struct device *dev,
+				      struct device_attribute *attr,
+				      const char *buf,
+				      size_t count)
+{
+	struct fblog_fb *fb = to_fblog_dev(dev);
+	unsigned long num;
+	int ret = 0;
+
+	num = simple_strtoul(buf, NULL, 10);
+
+	mutex_lock(&fb->info->lock);
+	if (num)
+		ret = fblog_open(fb);
+	else
+		fblog_close(fb, false);
+	mutex_unlock(&fb->info->lock);
+
+	return ret ? ret : count;
+}
+
+static DEVICE_ATTR(active, S_IRUGO | S_IWUSR | S_IWGRP, fblog_dev_active_show,
+		   fblog_dev_active_store);
+
 /*
  * fblog framebuffer list
  * The fblog_fbs[] array contains all currently registered framebuffers. If a
@@ -148,6 +188,7 @@ static void fblog_do_unregister(struct fb_info *info)
 	fblog_fbs[info->node] = NULL;
 
 	fblog_close(fb, true);
+	device_remove_file(&fb->dev, &dev_attr_active);
 	device_del(&fb->dev);
 	put_device(&fb->dev);
 }
@@ -156,6 +197,7 @@ static void fblog_do_register(struct fb_info *info, bool force)
 {
 	struct fblog_fb *fb;
 	int ret;
+	bool do_open = true;
 
 	fb = fblog_fbs[info->node];
 	if (fb && fb->info != info) {
@@ -186,7 +228,20 @@ static void fblog_do_register(struct fb_info *info, bool force)
 		return;
 	}
 
-	fblog_open(fb);
+	ret = device_create_file(&fb->dev, &dev_attr_active);
+	if (ret) {
+		pr_err("fblog: cannot create sysfs entry");
+		/* do not open fb if we cannot create control file */
+		do_open = false;
+	}
+
+	if (!activate_on_hotplug)
+		do_open = false;
+	if (main_only && info->node != 0)
+		do_open = false;
+
+	if (do_open)
+		fblog_open(fb);
 }
 
 static void fblog_register(struct fb_info *info, bool force)
@@ -321,6 +376,15 @@ static void __exit fblog_exit(void)
 	}
 }
 
+module_param(active, bool, S_IRUGO | S_IWUSR | S_IWGRP);
+MODULE_PARM_DESC(active, "Activate fblog rendering");
+
+module_param(activate_on_hotplug, bool, S_IRUGO | S_IWUSR | S_IWGRP);
+MODULE_PARM_DESC(activate_on_hotplug, "Activate fblog on hotplugged devices");
+
+module_param(main_only, bool, S_IRUGO);
+MODULE_PARM_DESC(main_only, "Activate fblog by default only on main devices");
+
 module_init(fblog_init);
 module_exit(fblog_exit);
 MODULE_LICENSE("GPL");
-- 
1.7.11.4