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virtio: console: Ensure only one process can have a port open at a time
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Add a guest_connected field that ensures only one process
can have a port open at a time.

This also ensures we don't have a race when we later add support for
dropping buffers when closing the char dev and buffer caching is turned
off for the particular port.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
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Amit Shah authored and Rusty Russell committed Feb 24, 2010
1 parent 2030fa4 commit 3c7969c
Showing 1 changed file with 17 additions and 1 deletion.
18 changes: 17 additions & 1 deletion drivers/char/virtio_console.c
Original file line number Diff line number Diff line change
Expand Up @@ -175,6 +175,9 @@ struct port {

/* Is the host device open */
bool host_connected;

/* We should allow only one process to open a port */
bool guest_connected;
};

/* This is the very early arch-specified put chars function. */
Expand Down Expand Up @@ -528,6 +531,8 @@ static int port_fops_release(struct inode *inode, struct file *filp)
/* Notify host of port being closed */
send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 0);

port->guest_connected = false;

return 0;
}

Expand All @@ -546,6 +551,16 @@ static int port_fops_open(struct inode *inode, struct file *filp)
if (is_console_port(port))
return -ENXIO;

/* Allow only one process to open a particular port at a time */
spin_lock_irq(&port->inbuf_lock);
if (port->guest_connected) {
spin_unlock_irq(&port->inbuf_lock);
return -EMFILE;
}

port->guest_connected = true;
spin_unlock_irq(&port->inbuf_lock);

/* Notify host of port being opened */
send_control_msg(filp->private_data, VIRTIO_CONSOLE_PORT_OPEN, 1);

Expand Down Expand Up @@ -709,6 +724,7 @@ int init_port_console(struct port *port)
pdrvdata.next_vtermno++;
list_add_tail(&port->cons.list, &pdrvdata.consoles);
spin_unlock_irq(&pdrvdata_lock);
port->guest_connected = true;

/* Notify host of port being opened */
send_control_msg(port, VIRTIO_CONSOLE_PORT_OPEN, 1);
Expand Down Expand Up @@ -856,7 +872,7 @@ static int add_port(struct ports_device *portdev, u32 id)
port->inbuf = NULL;
port->cons.hvc = NULL;

port->host_connected = false;
port->host_connected = port->guest_connected = false;

port->in_vq = portdev->in_vqs[port->id];
port->out_vq = portdev->out_vqs[port->id];
Expand Down

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