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vhost/vsock: use static minor number 

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Stefan Hajnoczi 2017-05-10 10:19:18 -04:00 committed by Greg Kroah-Hartman
parent ff35eb23de
commit f4660cc994
3 changed files with 7 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

4
Documentation/admin-guide/devices.txt
View File

@ -369,8 +369,10 @@
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
240 = /dev/userio Serio driver testing device
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)

4
drivers/vhost/vsock.c
View File

@ -706,7 +706,7 @@ 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,
};
@ -778,3 +778,5 @@ 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");

1
include/linux/miscdevice.h
View File

@ -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;