[Devel] [PATCH RH9 v5 06/10] drivers/vhost: add ioctl to increase the number of workers

[Andrey Zhadchenko]

Finally add ioctl to allow userspace to create additional workers
For now only allow to increase the number of workers

https://jira.sw.ru/browse/PSBM-139414
Signed-off-by: Andrey Zhadchenko <andrey.zhadchenko at virtuozzo.com>
---
v2:
 - Make code do what docs suggest. Previously ioctl-supplied new number
of workers were treated like an amount that should be added. Use new
number as a ceiling instead and add workers up to that number.

 drivers/vhost/vhost.c      | 32 +++++++++++++++++++++++++++++++-
 include/uapi/linux/vhost.h |  9 +++++++++
 2 files changed, 40 insertions(+), 1 deletion(-)

diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index b9a8d7b58cd8..d681352c9cbd 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -656,6 +656,25 @@ static int vhost_add_worker(struct vhost_dev *dev)
 	return err;
 }
 
+static int vhost_set_workers(struct vhost_dev *dev, int n)
+{
+	int i, ret;
+
+	if (n > dev->nvqs)
+		n = dev->nvqs;
+
+	if (n > VHOST_MAX_WORKERS)
+		n = VHOST_MAX_WORKERS;
+
+	for (i = 0; i < n - dev->nworkers ; i++) {
+		ret = vhost_add_worker(dev);
+		if (ret)
+			break;
+	}
+
+	return ret;
+}
+
 /* Caller should have device mutex */
 long vhost_dev_set_owner(struct vhost_dev *dev)
 {
@@ -1809,7 +1828,7 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 	struct eventfd_ctx *ctx;
 	u64 p;
 	long r;
-	int i, fd;
+	int i, fd, n;
 
 	/* If you are not the owner, you can become one */
 	if (ioctl == VHOST_SET_OWNER) {
@@ -1866,6 +1885,17 @@ long vhost_dev_ioctl(struct vhost_dev *d, unsigned int ioctl, void __user *argp)
 		if (ctx)
 			eventfd_ctx_put(ctx);
 		break;
+	case VHOST_SET_NWORKERS:
+		r = get_user(n, (int __user *)argp);
+		if (r < 0)
+			break;
+		if (n < d->nworkers) {
+			r = -EINVAL;
+			break;
+		}
+
+		r = vhost_set_workers(d, n);
+		break;
 	default:
 		r = -ENOIOCTLCMD;
 		break;
diff --git a/include/uapi/linux/vhost.h b/include/uapi/linux/vhost.h
index b2a27f623e9d..a180128d06ba 100644
--- a/include/uapi/linux/vhost.h
+++ b/include/uapi/linux/vhost.h
@@ -71,6 +71,15 @@
 #define VHOST_SET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x13, struct vhost_vring_state)
 #define VHOST_GET_VRING_ENDIAN _IOW(VHOST_VIRTIO, 0x14, struct vhost_vring_state)
 
+/* Set number of vhost workers
+ * Currently nuber of vhost workers can only be increased.
+ * All workers are freed upon reset.
+ * If the value is too big it is silently truncated to the maximum number of
+ * supported vhost workers
+ * Even if the error is returned it is possible that some workers were created
+ */
+#define VHOST_SET_NWORKERS _IOW(VHOST_VIRTIO, 0x1F, int)
+
 /* The following ioctls use eventfd file descriptors to signal and poll
  * for events. */
 
-- 
2.31.1