Re: Finding the slot in the ioconf table a module attaches to?

[Valery Ushakov <uwe%stderr.spb.ru@localhost>]

On Wed, Feb 01, 2023 at 08:27:57 -0500, Brad Spencer wrote:

> To add a bit...  generally I have just added an entry to one of the
> "major" files in sys/conf.  However, I have noticed that in order for
> the module to be able to use it, after the major file edit, I had to
> rebuild the kernel as well.  I have never been 100% sure that was proper
> behavior, but it seems to be the case.  That is, just editing the major
> file and building or rebuilding the module has not been enough.

.Xr devsw_attach 9

Major numbers (mapping "foo" -> 42, so that a program that opens a
node with major 42 gets to the device "foo") are a property of the
kernel config, so yes, you need to rebuild the kernel when you
introduce a new fixed major number.

When the module is loaded, the driver tells the kernel, "I'm `foo'".
It can also tell the kernel either "I'm ok with whatever major number
you give me", or it can tell "I want a specific major number N".  It's
an error to request a specific major N that is already taken (either
fixed in a major config file, or dynamically allocated to another
driver).

-uwe