From: Gregory Anders <greg@gpanders.com>
To: kernelnewbies@kernelnewbies.org
Subject: Device file not appearing
Date: Tue, 16 Mar 2021 14:25:07 -0600 [thread overview]
Message-ID: <YFEUI1OWtOQ7HcSy@gpanders.com> (raw)
Hi all,
I'm writing a char device driver and am having trouble getting the file
to appear under /dev.
This isn't my first rodeo: in fact, I've written a few other drivers in
the past and they have all worked as expected. This driver is based on
the source code of those other drivers, so I'm fairly confident I'm
doing everything correctly. So I'm stumped and looking for help.
Here is what I have in my init function:
#define DRIVER_NAME "foo"
static int __init mod_init(void)
{
dev_t devno;
my_class = class_create(THIS_MODULE, DRIVER_NAME);
ret = alloc_chrdev_region(&devno, 0, MAX_DEVICES, DRIVER_NAME);
my_major = MAJOR(devno);
...
}
(Note that for brevity I'm omitting a lot of boilerplate/error handling,
etc. But you can assume it's all there).
My driver is also a network driver; in fact, it's *primarily* a network
driver and it provides a char device file that is used to configure the
hardware. I am creating the char device whenever the network device is
first opened (e.g. 'netdev_open' below is the 'ndo_open' field of the
'struct netdev_ops'):
struct private_data {
struct cdev cdev;
...
}
static int netdev_open(struct net_device *dev)
{
struct private_data *priv = netdev_priv(dev);
dev_t devno;
int minor;
struct device *d;
minor = ida_alloc_max(&ida, MAX_DEVICES, GFP_KERNEL);
devno = MKDEV(my_major, minor);
cdev_init(&priv->cdev, &my_fops);
cdev_add(&priv->cdev, devno, 1);
/* This should create a device node with the same name as the
* network interface, e.g. foo0
*/
d = device_create(my_class, NULL, devno, priv, dev->name);
if (IS_ERR(d)) {
...
}
...
}
Again, I'm omitting the error checking for the sake of brevity, but it
is there in the actual code. This function runs successfully and the
network device is successfully opened. The 'device_create' function does
not return an error, but there is nothing beneath /dev as I would
expect.
I'm really stumped here because everything I've been able to find online
says that 'device_create' ought to create that device file. I can see my
class under /sys/class/ and that directory contains a directory with the
name of the device:
$ ls -1 /sys/class/my_class/
foo0
so it looks like the char device *is* being created, there's just no
corresponding entry under /dev.
Anyway, I know that's a lot of info. If you've made it this far, thanks
for reading. If you have any insight/advice/suggestions for me I'd
greatly appreciate it!
Thanks,
Greg
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next reply other threads:[~2021-03-21 18:48 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-03-16 20:25 Gregory Anders [this message]
2021-03-17 15:52 Device file not appearing Gregory Anders
2021-03-17 15:59 ` Greg KH
2021-03-17 16:13 ` Gregory Anders
2021-03-17 16:16 ` Greg KH
2021-03-17 16:56 ` Gregory Anders
2021-03-17 17:05 ` Gregory Anders
2021-03-17 17:15 ` Greg KH
2021-03-17 18:26 ` Gregory Anders
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