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Subject[PATCH] vhost/vsock: use static minor number
Date
Vhost-vsock is a software device so there is no probe call that causes
the driver to register its misc char device node. This creates a
chicken and egg problem: userspace applications must open
/dev/vhost-vsock to use the driver but the file doesn't exist until the
kernel module has been loaded.

Use the devname modalias mechanism so that /dev/vhost-vsock is created
at boot. The vhost_vsock kernel module is automatically loaded when the
first application opens /dev/host-vsock.

Note that the "reserved for local use" range in
Documentation/admin-guide/devices.txt is incorrect. The userio driver
already occupies part of that range. I've updated the documentation
accordingly.

Cc: device@lanana.org
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
Documentation/admin-guide/devices.txt | 3 ++-
include/linux/miscdevice.h | 1 +
drivers/vhost/vsock.c | 4 +++-
3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/Documentation/admin-guide/devices.txt b/Documentation/admin-guide/devices.txt
index c9cea2e..5fe3480 100644
--- a/Documentation/admin-guide/devices.txt
+++ b/Documentation/admin-guide/devices.txt
@@ -369,8 +369,9 @@
237 = /dev/loop-control Loopback control device
238 = /dev/vhost-net Host kernel accelerator for virtio net
239 = /dev/uhid User-space I/O driver support for HID subsystem
+ 241 = /dev/vhost-vsock Host kernel driver for virtio vsock

- 240-254 Reserved for local use
+ 242-254 Reserved for local use
255 Reserved for MISC_DYNAMIC_MINOR

11 char Raw keyboard device (Linux/SPARC only)
diff --git a/include/linux/miscdevice.h b/include/linux/miscdevice.h
index 762b5fe..58751ea 100644
--- a/include/linux/miscdevice.h
+++ b/include/linux/miscdevice.h
@@ -54,6 +54,7 @@
#define VHOST_NET_MINOR 238
#define UHID_MINOR 239
#define USERIO_MINOR 240
+#define VHOST_VSOCK_MINOR 241
#define MISC_DYNAMIC_MINOR 255

struct device;
diff --git a/drivers/vhost/vsock.c b/drivers/vhost/vsock.c
index 44eed8e..53e3e95 100644
--- a/drivers/vhost/vsock.c
+++ b/drivers/vhost/vsock.c
@@ -701,7 +701,7 @@ static const struct file_operations vhost_vsock_fops = {
};

static struct miscdevice vhost_vsock_misc = {
- .minor = MISC_DYNAMIC_MINOR,
+ .minor = VHOST_VSOCK_MINOR,
.name = "vhost-vsock",
.fops = &vhost_vsock_fops,
};
@@ -773,3 +773,5 @@ module_exit(vhost_vsock_exit);
MODULE_LICENSE("GPL v2");
MODULE_AUTHOR("Asias He");
MODULE_DESCRIPTION("vhost transport for vsock ");
+MODULE_ALIAS_MISCDEV(VHOST_VSOCK_MINOR);
+MODULE_ALIAS("devname:vhost-vsock");
--
2.9.3
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