mutual exclusion in vkbd

[Maksim Yevmenkin]

Norbert,

> I am currently trying to backport vkbd to FreeBSD 4.

ok

> Maksim Yevmenkin uses mtx_lock()/mtx_unlock() for
> protecting access to data structures under FreeBSD 5/6
> between the device functions and the kernel thread.
> 
> How should I best do this under FreeBSD 4?
> 
> Would something like splhigh() work in that context?
> Or should I use lockmgr with LK_EXCLUSIVE/LK_RELEASE?
> Is there any (pseudo)process context inside a kernel task?

spltty() is what you probably need to use. you could just adjust the 
following defines like

#define VKBD_LOCK_DECL		int
#define VKBD_LOCK_INIT(s)	/* noop */
#define VKBD_LOCK_DESTROY(s)	/* noop */	
#define VKBD_LOCK(s)		(s)->ks_lock = spltty()
#define VKBD_UNLOCK(s)		splx((s)->ks_lock)
#define VKBD_LOCK_ASSERT(s, w)
#define VKBD_SLEEP(s, f, d, t) \
	tsleep(&(s)->f, PCATCH | (PZERO + 1), d, t)

and you should be done. its not really required to store interrupt mask 
in softc structure, but this way its less changes to the code.

thanks,
max