linux-kernel - [PATCH v3 07/11] fblog: allow selecting fbs via sysfs

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Date:	Sun, 15 Jul 2012 21:04:42 +0200
From:	David Herrmann <dh.herrmann@...glemail.com>
To:	linux-kernel@...r.kernel.org
Cc:	Florian Tobias Schandinat <FlorianSchandinat@....de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	linux-fbdev@...r.kernel.org, linux-serial@...r.kernel.org,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	David Herrmann <dh.herrmann@...glemail.com>
Subject: [PATCH v3 07/11] fblog: allow selecting fbs via sysfs

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. Two
mechanisms to select framebuffers for fblog are added:

1) "active" module parameter: This parameter selects whether new
framebuffers are opened automatically. By default this is on, that is, all
framebuffers are automatically used by fblog during boot. By passing
fblog.active=0 you can deactivate this.
The init process can set this to 0 via
/sys/modules/fblog/parameters/active, too. However, this does not affect
already available and used framebuffers in any way.

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.

Signed-off-by: David Herrmann <dh.herrmann@...glemail.com>
---
 drivers/video/console/fblog.c | 53 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 52 insertions(+), 1 deletion(-)

diff --git a/drivers/video/console/fblog.c b/drivers/video/console/fblog.c
index 1c526c5..5519f91 100644
--- a/drivers/video/console/fblog.c
+++ b/drivers/video/console/fblog.c
@@ -44,6 +44,7 @@ struct fblog_fb {
 
 static DEFINE_MUTEX(fblog_registration_lock);
 static struct fblog_fb *fblog_fbs[FB_MAX];
+static bool active = 1;
 
 #define to_fblog_dev(_d) container_of(_d, struct fblog_fb, dev)
 
@@ -115,6 +116,40 @@ 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 +183,7 @@ 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 +192,7 @@ 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 +223,18 @@ 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 (!active)
+		do_open = false;
+
+	if (do_open)
+		fblog_open(fb);
 }
 
 static void fblog_register(struct fb_info *info, bool force)
@@ -321,6 +369,9 @@ static void __exit fblog_exit(void)
 	}
 }
 
+module_param(active, bool, S_IRUGO | S_IWUSR | S_IWGRP);
+MODULE_PARM_DESC(active, "Activate fblog by default");
+
 module_init(fblog_init);
 module_exit(fblog_exit);
 MODULE_LICENSE("GPL");
-- 
1.7.11.2

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