As part of the data migration work I'm doing, I've run into a few uvm
problems.

The problem is keeping uvm in sync with our archiving (backing up to
tape). When we begin archiving a file, we want to make sure that we flush
all dirty buffers out to disk. I think I know how to do this (sample code 
below). 

When we finish archiving, if we're marking the file as non-resident, we
want to blow away all of the relevant uvm pages. I think I also know how
to do this.

What I don't know how to do is to test and see if there are dirty pages
before blowing them away. I spoke w/ Jason, and he suggested posting here.
:-)

So what would we need to add? Something like a count of dirty pages
assosciated with the vnode? How would I access it?

Take care,

Bill

P.S. do these code snippents look right?

We have the vnode locked. To flush all pages:

        struct uvm_object *uobj = vp;
        simple_lock(&uobj->vmobjlock);
        uvn_flush(uobj, 0, 0, PGO_ALLPAGES | PGO_CLEANIT | PGO_SYNCIO);
        simple_unlock(&uobj->vmobjlock);

To blow away all pages:

        struct uvm_object *uobj = vp;
        simple_lock(&uobj->vmobjlock);
        uvn_flush(uobj, 0, 0, PGO_ALLPAGES | PGO_FREE); 
        simple_unlock(&uobj->vmobjlock);

??