linux-kernel - Re: [PATCH v1.2.26] wan: new driver retina

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Message-ID: <ca0148c30805312259v4d6a9344le94050ea9295eed8@mail.gmail.com>
Date:	Sun, 1 Jun 2008 08:59:55 +0300
From:	"Matti Linnanvuori" <mattilinn@...il.com>
To:	"Krzysztof Halasa" <khc@...waw.pl>
Cc:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1.2.26] wan: new driver retina

2008/5/30 Krzysztof Halasa <khc@...waw.pl>:
> "Matti Linnanvuori" <mattilinn@...il.com> writes:
>>>> +static int fepci_char_open(struct inode *inode, struct file *filp)
>>>> +{
>>>> +     unsigned int minor = MINOR(inode->i_rdev);
>>>> +     if (unlikely(minor >= find_cnt || card_privates[minor].pci_dev == NULL))
>>>> +             return -ENXIO;
>>>> +     filp->f_op = &fepci_char_fops;
>>>> +     if (unlikely(!try_module_get(THIS_MODULE)))
>>>> +             return -EBUSY;
>>>
>>> That won't work race-free, use owner field.
>>
>> You mean the f_op assignment? I have removed that.
>
> Actually I meant try_module_get() from within the driver, for example
> your module may get unloaded while in this function, before this
> try_module_get(), and that would be fatal.

I don't think the module can finish getting unloaded while in that
function because the module cleanup function unregisters the
character device.

> Yes, I thought stream mode = character device but now I see it's
> another flavour of network device(?), which is never up and exists
> only for the ability to receive netdev ioctls (though it also uses
> char dev ioctls).
>
> Did I get this right?

Yeah.

> Why not simply use a character device, with normal read, write etc?

It would make more sense to use a character device. Read and write
system calls consume more CPU time, though.
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