Make MOD_QUIESCE a bit more useful..

[John Baldwin]

So currently the MOD_QUIESCE event is posted to a module when unloading a kld 
so it can veto non-forced unloads.  However, the current implementation in 
the kernel linker is to run through all the modules in a file, posting 
MOD_QUIESCE followed by MOD_UNLOAD on each module serially.  Thus, if you 
have multiple modules in a single kld and one of the modules veto's an unload 
request via MOD_QUIESCE, you don't know as the module author if any of your 
modules were unloaded via MOD_UNLOAD or not.  I think a better approach would 
be to change the kernel linker to invoke MOD_QUIESCE on all modules in a 
single pass first.  If none of those fail (or it's a forced unload), then it 
can do a second pass invoking MOD_UNLOAD on all the modules.

-- 
John Baldwin