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Re: How to make character devices in non spec-fs file systems
On Thursday 29 October 2009 12:17:53 der Mouse wrote:
> >> Eh? I don't understand. Your character devices should be VCHR.
> > Yes, but if I do that, the VFS code in the kernel will call specfs
> > functions on my vnode, because there are hardcoded checks like:
> > if (vn->v_type == VCHR)
> > call into specfs code(vn);
> Yes. That's how device special files work.
Yes, but I am not using specfs. I want to redirect the VCHR vnops directly to
> > And because my vnode is not initialised by specfs, it panics. I am
> > not using specfs for my character device. I am using a separately
> > mounted filesystem called "FreeBSD devfs".
> specfs is not a filesystem in the sense of something mountable. It's a
> collection of code for implementing various special things, such as
> device special files, which othewise would mean a bunch of relatively
> complicated code duplicated in every device-supporting filesystem. I'd
> suggest you look at how existing filesystems, like ffs and nfs,
> implement VCHR and VBLK vnodes; that should be able to guide you in
> when and how you need to make calls into the specfs code.
From what I understand ffs and nfs only allow node creation. ffs and nfs does
not handle any read/write requests, for example, on a character device, right?
That is where the difference is. I've implemented something similar to ffs,
only that when the character device file residing in my devfs is opened the
ffs [example] gets the read/write and not specfs. Do you see?
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