dahdi: Add module parameter to limit number of pseudo channels.

Since there isn't a fixed array to hold all the channels, and also limit
the total number of channels that can be created, we'll add a module
parameter to allow the system administrator to specify the maximum
number of pseudo channels.  This is to prevent a potentially
non-privledged process from consuming too much CPU (since all pseudos
are checked each "tick" for conferencing) and kernel memory.

By default the number of pseudo channels is limited to 512.  Change the
default limit with:

]# modprobe dahdi max_pseudo_channels=<new limit>

or at runtime with:

]# echo <new limit> > /sys/module/dahdi/parameters/max_psuedo_channels

Signed-off-by: Shaun Ruffell <sruffell@digium.com>
Acked-by: Kinsey Moore <kmoore@digium.com>

git-svn-id: http://svn.asterisk.org/svn/dahdi/linux/trunk@9610 a0bf4364-ded3-4de4-8d8a-66a801d63aff

1 files changed, 18 insertions, 8 deletions

diff --git a/drivers/dahdi/dahdi-base.c b/drivers/dahdi/dahdi-base.c
index 60e2d72..0c9d9f3 100644
--- a/drivers/dahdi/dahdi-base.c
+++ b/drivers/dahdi/dahdi-base.c
@@ -3003,7 +3003,10 @@ static int can_open_timer(void)
 #endif
 }
 
-static struct dahdi_chan *dahdi_alloc_pseudo(void)
+static unsigned int max_pseudo_channels = 512;
+static unsigned int num_pseudo_channels;
+
+static struct dahdi_chan *dahdi_alloc_pseudo(struct file *file)
 {
 	struct pseudo_chan *pseudo;
 	unsigned long flags;
@@ -3016,6 +3019,9 @@ static struct dahdi_chan *dahdi_alloc_pseudo(void)
 	if (!can_open_timer())
 		return NULL;
 
+	if (unlikely(num_pseudo_channels >= max_pseudo_channels))
+		return NULL;
+
 	pseudo = kzalloc(sizeof(*pseudo), GFP_KERNEL);
 	if (NULL == pseudo)
 		return NULL;
@@ -3059,9 +3065,12 @@ static struct dahdi_chan *dahdi_alloc_pseudo(void)
 	snprintf(pseudo->chan.name, sizeof(pseudo->chan.name)-1,
 		 "Pseudo/%d", pseudo->chan.channo);
 
+	file->private_data = &pseudo->chan;
+
 	/* Once we place the pseudo chan on the list...it's registered and
 	 * live. */
 	spin_lock_irqsave(&chan_lock, flags);
+	++num_pseudo_channels;
 	list_add(&pseudo->node, pos);
 	spin_unlock_irqrestore(&chan_lock, flags);
 
@@ -3082,6 +3091,7 @@ static void dahdi_free_pseudo(struct dahdi_chan *chan)
 
 	spin_lock_irqsave(&chan_lock, flags);
 	list_del(&pseudo->node);
+	--num_pseudo_channels;
 	spin_unlock_irqrestore(&chan_lock, flags);
 
 	dahdi_chan_unreg(chan);
@@ -3127,13 +3137,10 @@ static int dahdi_open(struct inode *inode, struct file *file)
 	if (unit == DAHDI_CHANNEL)
 		return dahdi_chan_open(file);
 	if (unit == DAHDI_PSEUDO) {
-		chan = dahdi_alloc_pseudo();
-		if (chan) {
-			file->private_data = chan;
-			return dahdi_specchan_open(file);
-		} else {
-			return -ENXIO;
-		}
+		chan = dahdi_alloc_pseudo(file);
+		if (unlikely(!chan))
+			return -ENOMEM;
+		return dahdi_specchan_open(file);
 	}
 	return dahdi_specchan_open(file);
 }
@@ -9050,6 +9057,9 @@ MODULE_PARM_DESC(debug, "Sets debugging verbosity as a bitfield, to see"\
 		" this to 32");
 module_param(deftaps, int, 0644);
 
+module_param(max_pseudo_channels, int, 0644);
+MODULE_PARM_DESC(max_pseudo_channels, "Maximum number of pseudo channels.");
+
 static const struct file_operations dahdi_fops = {
 	.owner   = THIS_MODULE,
 	.open    = dahdi_open,