um: vfio: Support adding devices via mconsole

It can be used when we want to pass through PCI devices to UML
while it's up and running. PCI devices can be passed through to
UML using the same syntax as the command line option:

(mconsole) config vfio_uml.device=<domain:bus:slot.function>

Signed-off-by: Tiwei Bie <[email protected]>
Link: https://patch.msgid.link/[email protected]
Signed-off-by: Johannes Berg <[email protected]>

Author: btw616

arch/um/drivers/vfio_kern.c

@@ -16,6 +16,7 @@
 #include <init.h>
 #include <os.h>
 
+#include "mconsole_kern.h"
 #include "virt-pci.h"
 #include "vfio_user.h"
 
@@ -60,6 +61,7 @@ static LIST_HEAD(uml_vfio_groups);
 static DEFINE_MUTEX(uml_vfio_groups_mtx);
 
 static LIST_HEAD(uml_vfio_devices);
+static DEFINE_MUTEX(uml_vfio_devices_mtx);
 
 static int uml_vfio_set_container(int group_fd)
 {
@@ -581,32 +583,44 @@ static struct uml_vfio_device *uml_vfio_find_device(const char *device)
 	return NULL;
 }
 
-static int uml_vfio_cmdline_set(const char *device, const struct kernel_param *kp)
+static struct uml_vfio_device *uml_vfio_add_device(const char *device)
 {
 	struct uml_vfio_device *dev;
 	int fd;
 
+	guard(mutex)(&uml_vfio_devices_mtx);
+
 	if (uml_vfio_container.fd < 0) {
 		fd = uml_vfio_user_open_container();
 		if (fd < 0)
-			return fd;
+			return ERR_PTR(fd);
 		uml_vfio_container.fd = fd;
 	}
 
 	if (uml_vfio_find_device(device))
-		return -EEXIST;
+		return ERR_PTR(-EEXIST);
 
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
 	if (!dev)
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 
 	dev->name = kstrdup(device, GFP_KERNEL);
 	if (!dev->name) {
 		kfree(dev);
-		return -ENOMEM;
+		return ERR_PTR(-ENOMEM);
 	}
 
 	list_add_tail(&dev->list, &uml_vfio_devices);
+	return dev;
+}
+
+static int uml_vfio_cmdline_set(const char *device, const struct kernel_param *kp)
+{
+	struct uml_vfio_device *dev;
+
+	dev = uml_vfio_add_device(device);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
 	return 0;
 }
 
@@ -629,6 +643,42 @@ __uml_help(uml_vfio_cmdline_param_ops,
 "    through multiple PCI devices to UML.\n\n"
 );
 
+static int uml_vfio_mc_config(char *str, char **error_out)
+{
+	struct uml_vfio_device *dev;
+
+	if (*str != '=') {
+		*error_out = "Invalid config";
+		return -EINVAL;
+	}
+	str += 1;
+
+	dev = uml_vfio_add_device(str);
+	if (IS_ERR(dev))
+		return PTR_ERR(dev);
+	uml_vfio_open_device(dev);
+	return 0;
+}
+
+static int uml_vfio_mc_id(char **str, int *start_out, int *end_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static int uml_vfio_mc_remove(int n, char **error_out)
+{
+	return -EOPNOTSUPP;
+}
+
+static struct mc_device uml_vfio_mc = {
+	.list           = LIST_HEAD_INIT(uml_vfio_mc.list),
+	.name           = "vfio_uml.device",
+	.config         = uml_vfio_mc_config,
+	.get_config     = NULL,
+	.id             = uml_vfio_mc_id,
+	.remove         = uml_vfio_mc_remove,
+};
+
 static int __init uml_vfio_init(void)
 {
 	struct uml_vfio_device *dev, *n;
@@ -639,6 +689,8 @@ static int __init uml_vfio_init(void)
 	list_for_each_entry_safe(dev, n, &uml_vfio_devices, list)
 		uml_vfio_open_device(dev);
 
+	mconsole_register_dev(&uml_vfio_mc);
+
 	return 0;
 }
 late_initcall(uml_vfio_init);