virtio: console: Send SIGIO to processes that request it for host events

A process can request for SIGIO on host connect / disconnect events
using the O_ASYNC file flag using fcntl().

If that's requested, and if the guest-side connection for the port is
open, any host-side open/close events for that port will raise a SIGIO.
The process can then use poll() within the signal handler to find out
which port triggered the signal.

Signed-off-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 25 insertions, 0 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index c84486b3e43d..c4ca43694233 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -196,6 +196,9 @@ struct port {
         /* The 'name' of the port that we expose via sysfs properties */
         char *name;
 
+        /* We can notify apps of host connect / disconnect events via SIGIO */
+        struct fasync_struct *async_queue;
+
         /* The 'id' to identify the port with the Host */
         u32 id;
 
@@ -815,6 +818,14 @@ out:
         return ret;
 }
 
+static int port_fops_fasync(int fd, struct file *filp, int mode)
+{
+        struct port *port;
+
+        port = filp->private_data;
+        return fasync_helper(fd, filp, mode, &port->async_queue);
+}
+
 /*
  * The file operations that we support: programs in the guest can open
  * a console device, read from it, write to it, poll for data and
@@ -828,6 +839,7 @@ static const struct file_operations port_fops = {
         .write = port_fops_write,
         .poll  = port_fops_poll,
         .release = port_fops_release,
+        .fasync = port_fops_fasync,
 };
 
 /*
@@ -1086,6 +1098,12 @@ static unsigned int fill_queue(struct virtqueue *vq, spinlock_t *lock)
         return nr_added_bufs;
 }
 
+static void send_sigio_to_port(struct port *port)
+{
+        if (port->async_queue && port->guest_connected)
+                kill_fasync(&port->async_queue, SIGIO, POLL_OUT);
+}
+
 static int add_port(struct ports_device *portdev, u32 id)
 {
         char debugfs_name[16];
@@ -1108,6 +1126,7 @@ static int add_port(struct ports_device *portdev, u32 id)
         port->name = NULL;
         port->inbuf = NULL;
         port->cons.hvc = NULL;
+        port->async_queue = NULL;
 
         port->cons.ws.ws_row = port->cons.ws.ws_col = 0;
 
@@ -1362,6 +1381,12 @@ static void handle_control_message(struct ports_device *portdev,
                 spin_lock_irq(&port->outvq_lock);
                 reclaim_consumed_buffers(port);
                 spin_unlock_irq(&port->outvq_lock);
+
+                /*
+                 * If the guest is connected, it'll be interested in
+                 * knowing the host connection state changed.
+                 */
+                send_sigio_to_port(port);
                 break;
         case VIRTIO_CONSOLE_PORT_NAME:
                 /*